In its most general sense, is the art of dissecting, or artificially separating and taking to pieces the different parts of organized bodies, in order to an exact discovery of their situation, structure, and economy; but here we limit its signification to animal bodies. The word is Greek, ἀνατομία; derived from ἀνατέμνω, to dissect, or separate by cutting.

INTRODUCTION.

§ 1. History of Anatomy.

This art seems to have been very ancient; though, for a long time, known only in an imperfect manner.—The first men who lived must have soon acquired some notion of the structure of their own bodies, particularly of the external parts, and of some even of the internal, such as bones, joints, and sinews, which are exposed to the examination of the senses in living bodies. This rude knowledge must have been gradually improved, by the accidents to which the body is exposed, by the necessities of life, and by the various customs, ceremonies, and superstitions, of different nations. Thus, the observance of bodies killed by violence, attention to wounded men, and to many diseases, the various ways of putting criminals to death, the funeral ceremonies, and a variety of such things, must have shown men every day more and more of themselves; especially as curiosity and self-love would here urge them powerfully to observation and reflection.

The brute creation having such an affinity to man in outward form, motion, senses, and ways of life; the generation of the species, and the effect of death upon the body, being observed to be so nearly the same in both; the conclusion was not only obvious, but unavoidable, that their bodies were formed nearly upon the same model. And the opportunities of examining the bodies of brutes were so easily procured, indeed so necessarily occurred in the common business of life, that the huntsman in making use of his prey, the priest in sacrificing, the angur inclination, and above all, the butcher, or those who might out of curiosity attend upon his operations, must have been daily adding to the little stock of anatomical knowledge. Accordingly we find, in fact, that the South sea islanders, who have been left to their own observation and reasoning, without the assistance of letters, have yet a considerable share of rude or wild anatomical and physiological knowledge. Dr Hunter informs us, that when Omai was in his museum with Mr Banks, though he could not explain himself intelligibly, they plainly saw that he knew the principal parts of the body, and something likewise of their uses; and manifested a great curiosity or desire of having the functions of the internal parts of the body explained to him; particularly the relative functions of the two sexes, which with him seemed to be the most interesting object of the human mind.

We may further imagine, that the philosophers of the most early ages, that is, the men of curiosity, observation, experience, and reflection, could not overlook an instance of natural organization, which was so interesting, and at the same time so wonderful, more especially such of them as applied to the study and cure of diseases. We know that physic was a branch of philosophy till the age of Hippocrates.

Thus the art must have been circumstanced in its beginning. We shall next see from the testimony of historians histories, historians and other writers, how it actually appeared as an art, from the time that writing was introduced among men; how it was improved, and conveyed down to us through a long series of ages.

Civilization, and improvements of every kind, would naturally begin in fertile countries and healthful climates, where there would be leisure for reflection, and an appetite for amusement. Accordingly, writing, and many other useful and ornamental inventions and arts, appear to have been cultivated in the eastern parts of Asia long before the earliest times that are treated of by the Greek or other European writers; and that the arts and learning of those eastern people were in subsequent times gradually communicated to adjacent countries, especially by the medium of traffic. The customs, superstitions, and climate of eastern countries, however, appear to have been as unfavourable to practical anatomy as they were inviting to the study of astronomy, geometry, poetry, and all the softer arts of peace.

Animal bodies there run so quickly into nauseous putrefaction, that the earliest inhabitants must have avoided such offensive employments as anatomical inquiries, like their posterity at this day. And in fact it does not appear, by the writings of the Grecians, or Jews, or Phoenicians, or of other eastern countries, that anatomy was particularly cultivated by any of those eastern nations. In tracing it backwards to its infancy, we cannot go farther into antiquity than the times of the Grecian philosophers. As an art in the state of some cultivation, it may be said to have been brought forth and bred up among them as a branch of natural knowledge.

The era of philosophy, as it was called, began with Thales the Milesian being declared, by a very general consent of the people, the most wise of all the Grecians, 480 years before Christ. The philosophers of his school, which was called the Ionian, cultivated principally natural knowledge. Socrates, the seventh in succession of their great teachers, introduced the study of morals, and was thence said to bring down philosophy from heaven, to make men truly wise and happy.

In the writings of his scholar and successor Plato, we see that the philosophers had carefully considered the human body, both in its organization and functions; and though they had not arrived at the knowledge of the more minute and intricate parts, which required the successive labour and attention of many ages, they had made up very noble and comprehensive ideas of the subject in general. The anatomical descriptions of Xenophon and Plato have had the honour of being quoted by Longinus (§ xxxii.) as specimens of sublime writing; and the extract from Plato is still more remarkable for its containing the rudiments of the circulation of the blood. "The heart (says Plato) is the centre or knot of the blood-vessels, the spring or fountain of the blood, which is carried impetuously round; the blood is the paludum or food of the flesh; and for the purpose of nourishment, the body is laid out into canals, like those which are drawn through gardens, that the blood may be conveyed, as from a fountain, to every part of the previous body."

Hippocrates was nearly contemporary with the great philosophers of whom we have been speaking, about 400 years before the Christian era. He is said to have separated the profession of philosophy and physic, and to have been the first who applied to physic alone as the business of his life. He is likewise generally supposed to be the first who wrote upon anatomy. We know of nothing that was written expressly upon the subject before; and the first anatomical dissection which has been recorded was made by his friend Democritus of Abdera.

If, however, we read the works of Hippocrates with impartiality, and apply his accounts of the parts to what we know of the human body, we must allow his descriptions to be imperfect, incorrect, sometimes extravagant, and often unintelligible, that of the bones only excepted. He seems to have studied these with more success than the other parts, and tells us that he had an opportunity of seeing a human skeleton.

From Hippocrates to Galen, who flourished towards the end of the second century, in the decline of the Roman empire, that is, in the space of 600 years, anatomy was greatly improved; the philosophers still considering it as a most curious and interesting branch of natural knowledge, and the physicians as a principal foundation of their art. Both of them, in that interval of time, contributed daily to the common stock, by more accurate and extended observations, and by the lights of improving philosophy.

As these two great men had applied very particularly to the study of animal bodies, they not only made great improvements, especially in physiology, but raised the credit of natural knowledge, and spread it as wide as Alexander's empire.

Few of Aristotle's writings were made public in his lifetime. He affected to say that they would be unintelligible to those who had not heard them explained at his lectures; and, except the use which Theophrastus made of them, they were lost to the public for above 130 years after the death of Theophrastus; and at last came out defective from bad preservation, and corrupted by men, who, without proper qualifications, presumed to correct and to supply what was lost.

From the time of Theophrastus, the study of natural knowledge at Athens was for ever on the decline; and the reputation of the Lyceum and Academy was almost confined to the studies which are subservient to oratory and public speaking.

The other great institution for Grecian education was at Alexandria in Egypt. The first Ptolemies, both from their love of literature, and to give true and permanent dignity to their empire, and to Alexander's favourite city, set up a grand school in the palace itself, with a museum and a library, which, we may say, has been the most famed in the world. Anatomy among other sciences, was publicly taught; and the two distinguished anatomists were Erasistratus the pupil and friend of Theophrastus, and Herophilus. Their voluminous works are all lost; but they are quoted by Galen almost in every page. These professors were probably the first who were authorized to dissect human bodies; a peculiarity which marks strongly the philosophical magnanimity of the first Ptolemy, and fixes a great era in the history of anatomy. And it was, no doubt, from this particular advantage which the Alexandrians had above all others, that their school not only gained, but for many centuries preserved, the first reputation. Ammianus Marcellinus, who lived about 650 years after the schools were set up, says, they were so famous in his time, that it was enough to secure credit to any physician if he could say he had studied at Alexandria.

Herophilos has been said to have anatomized 700 bodies. We must allow for exaggeration. Nay, it was said, that both he and Erasistratus made it a common practice to open living bodies, that they might discover the more secret springs of life. But this, no doubt, was only a vulgar opinion, arising from the prejudices of mankind; and accordingly, without any good reason, such tales have been told of modern anatomists, and have been believed by the vulgar.

Among the Romans, though it is probable they had physicians and surgeons from the foundation of the city, yet we have no account of any of these applying themselves to anatomy for a very long time. Archagathus was the first Greek physician established in Rome, and he was banished the city on account of the severity of his operations.—Asclepiades, who flourished in Rome 101 years after Archagathus, in the time of Pompey, attained such a high reputation as to be ranked in the same class with Hippocrates. He seemed to have some notion of the air in respiration acting by its weight; and in accounting for digestion, he supposed the food to be no farther changed than by a commination into extremely small parts, which being distributed to the several parts of the body, is assimilated to the nature of each. One Cassius, commonly thought to be a disciple of Asclepiades, accounted for the right side of the body becoming paralytic on hurting the left side of the brain in the same manner as has been done by the moderns, viz. from the crossing of the nerves from the right to the left side of the brain.

From the time of Asclepiades to the second century, physicians seem to have been greatly encouraged at Rome; and in the writings of Celsus, Rufus, Pliny, Caelius Aurelianus, and Arateus, we find several anatomical observations, but mostly very superficial and inaccurate. Towards the end of the second century lived Claudius Galenus Pergamus, whose name is so well known in the medical world. He applied himself particularly to the study of anatomy, and did more in that way than all that went before him. He seems, however, to have been at a great loss for human subjects to operate upon; and therefore his descriptions of the parts are mostly taken from brute animals. His works contain the fullest history of anatomists, and the most complete system of the science, to be met with anywhere before him, or for several centuries after; so that a number of passages in them were reckoned absolutely unintelligible for many ages, until explained by the discoveries of succeeding anatomists.

About the end of the fourth century, Nemesius bishop of Emissa wrote a treatise on the nature of man, in which it is said were contained two celebrated modern discoveries; the one, the uses of the bile, boasted of by Sylvius de la Boe; and the other, the circulation of the blood. This last, however, is proved by Dr Freind, in his History of Physic, p. 229, to be falsely ascribed to this author.

The Roman empire beginning now to be oppressed by the barbarians, and sunk in gross superstition, learning of all kinds decreased; and when the empire was totally overwhelmed by those barbarous nations, every appearance of science was almost extinguished in Europe. The only remains of it were among the Arabians in Spain and in Asia.—The Saracens, who came into Spain, destroyed at first all the Greek books which the Vandals had spared; but though the government was in a constant struggle and fluctuation during 800 years before they were driven out, they received a taste for learning from their countrymen of the east; several of their princes encouraged liberal studies; public schools were set up at Cordova, Toledo, and other towns, and translations of the Greeks into the Arabic were universally in the hands of their teachers.

Thus was the learning of the Grecians transferred to the Arabians. But though they had so good a foundation to build upon, this art was never improved while they were masters of the world; for they were satisfied with commenting upon Galen, and seem to have made no dissection of human bodies.

Abdallatiph, who was himself a teacher of anatomy, a man eminent in his time (at and about 1202) for his learning and curiosity; a great traveller, who had been bred at Bagdad, and had seen many of the great cities and principal places for study in the Saracen empire; who had a favourable opinion of original observation, in opposition to book learning; who boldly corrected some of Galen's errors, and was persuaded that many more might be detected: this man, we say, never made or saw, or seemed to think of a human dissection. He discovered Galen's errors in the osteology, by going to burying grounds, with his students and others, where he examined and demonstrated the bones; he earnestly recommended that method of study, in preference even to the reading of Galen, and thought that many farther improvements might be made; yet he seemed not to have an idea that a fresh subject might be dissected with that view.

Perhaps the Jewish tenets which the Mahometans adopted about uncleanness and pollution, might prevent their handling dead bodies; or their opinion of what was supposed to pass between an angel and the dead person, might make them think disturbing the dead highly sacrilegious. Such, however, as Arabian learning was, for many ages together there was hardly any other in all the western countries of Europe. It was introduced by the establishment of the Saracens in Spain in 711, and kept its ground till the restoration of learning in the end of the 15th century. The state of anatomy in Europe, in the times of Arabian influence, may be seen by reading a very short system of anatomy drawn up by Mundinus, in the year 1315. It was principally extracted from what the Arabians had preserved of Galen's doctrine; and, rude as it is, in that age it was judged to be so masterly a performance, that it was ordered by a public decree, that it should be read in all the schools of Italy; and it actually continued to be almost the only book which was read upon the subject for above 200 years. Cortesius gives him the credit of being the great restorer of anatomy, and the first who dissected human bodies among the moderns.

A general prejudice against dissection, however, prevailed till the 16th century. The emperor Charles V. ordered a consultation to be held by the divines of Salamanca, in order to determine whether or not it was lawful lawful in point of conscience to dissect a dead body.

In Moscow, till very lately, both anatomy and the use of skeletons were forbidden; the first as inhuman, and the latter as subservient to witchcraft.

In the beginning of the 15th century, learning revived considerably in Europe, and particularly physic, by means of copies of the Greek authors brought from the sack of Constantinople; after which the number of anatomists and anatomical books increased to a prodigious degree. The Europeans becoming thus possessed of the ancient Greek fathers of medicine, were for a long time so much occupied in correcting the copies they could obtain, studying the meaning, and commenting upon them, that they attempted nothing of their own, especially in anatomy.

And here the late Dr Hunter introduces into the annals of this art, a genius of the first rate, Leonardo da Vinci, who had been formerly overlooked, because he was of another profession, and because he published nothing upon the subject. He is considered by the doctor as by far the best anatomist and physiologist of his time: and was certainly the first man we know of who introduced the practice of making anatomical drawings.

Vassare, in his Lives of the Painters, speaks of Leonardo thus, after telling us that he had composed a book of the anatomy of a horse, for his own study: "He afterwards applied himself with more diligence to the human anatomy; in which study he reciprocally received and communicated assistance to Marc Antonio della Torre, an excellent philosopher, who then read lectures in Pavia, and wrote upon this subject; and who was the first, as I have heard, who began to illustrate medicine from the doctrine of Galen, and to give true light to anatomy, which till that time had been involved in clouds of darkness and ignorance. In this he availed himself exceedingly of the genius and labour of Leonardo, who made a book of studies, drawn with red chalk, and touched with a pen, with great diligence, of such objects as he had himself dissected; where he made all the bones, and to those he joined, in their order, all the nerves, and covered them with the muscles. And concerning those, from part to part, he wrote remarks in letters of an ugly form, which are written by the left hand, backwards, and not to be understood but by those who know the method of reading them; for they are not to be read without a looking-glass. Of these papers of the human anatomy, there is a great part in the possession of M. Francesco da Melzo, a Milanese gentleman, who, in the time of Leonardo, was a most beautiful boy, and much beloved by him, as he is now a beautiful and genteel old man, who reads those writings, and carefully preserves them, as precious relics, together with the portrait of Leonardo of happy memory. It appears impossible that that divine spirit should reason so well upon the arteries, and muscles, and nerves, and veins; and with such diligence of every thing," &c. &c.

Those very drawings and the writings are happily found to be preserved in his majesty's great collection of original drawings, where the doctor was permitted to examine them; and his sentiments upon the occasion he thus expresses: "I expected to see little more than such designs in anatomy as might be useful to a painter in his own profession; but I saw, and indeed with astonishment, that Leonardo had been a general and a deep student. When I consider what pains he has taken upon every part of the body, the superiority of his universal genius, his particular excellence in mechanics and hydraulics, and the attention with which such a man would examine and see objects which he was to draw, I am fully persuaded that Leonardo was the best anatomist at that time in the world. We must give the 15th century the credit of Leonardo's anatomical studies, as he was 55 years of age at the close of that century."

In the beginning of the 16th century, Achillius and Benedictus, but particularly Berengarius and Massa, followed out the improvement of anatomy in Italy, where they taught it, and published upon the subject. These first improvers made some discoveries from their own dissections: but it is not surprising that they should have been diffident of themselves, and have followed Galen almost blindly, when his authority had been so long established, and when the enthusiasm for Greek authors was rising to such a pitch.

Soon after this, we may say about the year 1540, the great Vesalius appeared. He was studious, laborious, and ambitious. From Brussels, the place of his birth, he went to Louvain, and thence to Paris, where anatomy was not yet making a considerable figure; and then to Louvain to teach; from which place, very fortunately for his reputation, he was called to Italy, where he met with every opportunity that such a genius for anatomy could desire, that is, books, subjects, and excellent draughtsmen. He was equally laborious in reading the ancients, and in dissecting bodies. And in making the comparison, he could not but see, that there was great room for improvement, and that many of Galen's descriptions were erroneous. When he was but a young man, he published a noble system of anatomy, illustrated with a great number of elegant figures.—In this work he found so many occasions of correcting Galen, that his contemporaries, partial to antiquity, and jealous of his reputation, complained that he carried his turn for improvement and criticisms to licentiousness. The spirit of opposition and emulation was presently roused; and Sylvius in France, Columbus, Fallopius, and Eustachius in Italy, who were all in high anatomical reputation about the middle of this 16th century, endeavoured to defend Galen at the expense of Vesalius. In their disputes they made their appeals to the human body: and thus in a few years the art was greatly improved. And Vesalius being detected in the very fault which he condemns in Galen, to wit, describing from the dissections of brutes, and not of the human body, it exposed so fully that blunder of the older anatomists, that in succeeding times there has been little reason for such complaint.—Besides the above, he published several other anatomical treatises. He has been particularly serviceable by imposing names on the muscles, most of which are retained to this day. Formerly they were distinguished by numbers, which were differently applied by almost every author.

In 1561, Gabriel Fallopius, professor of anatomy at Padua, published a treatise of anatomy under the title of Observations Anatomicae. This was designed as a supplement to Vesalius; many of whose descriptions he corrects, though he always makes mention of him. in an honourable manner. Fallopius made many great discoveries, and his book is well worth the perusal of every anatomist.

In 1563, Bartholomaeus Eustachius published his Opuscula Anatomica at Venice, which have ever since been justly admired for the exactness of the descriptions, and the discoveries contained in them. He published afterwards some other pieces; in which there is little of anatomy; but never published the great work he had promised, which was to be adorned with copperplates representing all the parts of the human body. These plates, after lying buried in an old cabinet for upwards of 150 years, were at last discovered and published in the year 1714, by Lancisi the pope's physician; who added a short explication text, because Eustachius's own writing could not be found.

From this time the study of anatomy gradually diffused itself over Europe; insomuch that for the last hundred years it has been daily improving by the labour of a number of professed anatomists almost in every country of Europe.

We may form a judgment about the state of anatomy even in Italy, in the beginning of the 17th century, from the information of Cortesius. He had been professor of anatomy at Bologna, and was then professor of medicine at Massana; where, though he had a great desire to improve himself in the art, and to finish a treatise which he had begun on practical anatomy, in 24 years he could twice only procure an opportunity of dissecting a human body; and then it was with difficulties and in hurry; whereas he had expected to have done so, he says, once every year, according to the custom in the famous academies of Italy.

In the very end of the 16th century, our great Harvey, as was the custom of the times, went to Italy to study medicine; for Italy was still the favourite seat of the arts: And in the very beginning of the 17th century, soon after Harvey's return to England, his master in anatomy, Fabricius ab Aquapendente, published an account of the valves in the veins, which he had discovered many years before, and no doubt taught in his lectures when Harvey attended them.

This discovery evidently affected the established doctrine of all ages, that the veins carried the blood from the liver to all parts of the body for nourishment. It set Harvey to work upon the use of the heart and vascular systems in animals; and in the course of some years he was so happy as to discover, and to prove beyond all possibility of doubt, the circulation of the blood. He taught his new doctrine in his lectures about the year 1616, and printed it in 1628.

It was by far the most important step that has been made in the knowledge of animal bodies in any age. It not only reflected useful lights upon what had been already found out in anatomy, but also pointed out the means of further investigation. And accordingly we see, that from Harvey to the present time, anatomy has been so much improved, that we may reasonably question if the ancients have been further outdone by the moderns in any other branch of knowledge. From one day to another there has been a constant succession of discoveries, relating either to the structure or functions of our bodies; and new anatomical processes, both of investigation and demonstration, have been daily invented. Many parts of the body which were not known in Harvey's time have since then been brought to light: and of those which were known, the internal composition and functions remained unexplained; and indeed must have remained inexplicable without the knowledge of the circulation.

Harvey's doctrine at first met with considerable opposition; but in the space of about 20 years it was so generally and so warmly embraced, that it was imagined every thing in physic would be explained. But time and experience have taught us, that we still are, and probably must long continue to be, very ignorant; and that in the study of the human body, and of its diseases, there will always be an extensive field for the exercise of sagacity.

After the discovery and knowledge of the circulation of the blood, the next question would naturally have been about the passage and route of the nutritious part of the food or chyle from the bowels to the blood vessels: And, by good fortune, in a few years after Harvey had made his discovery, Asellius, an Italian physician, found out the lacteals, or vessels which carry the chyle from the intestines; and printed his account of them, with coloured prints, in the year 1627, the very year before Harvey's book came out.

For a number of years after these two publications, the anatomists in all parts of Europe were daily opening living dogs, either to see the lacteals or to observe the phenomena of the circulation. In making an experiment of this kind, Pecquet in France was fortunate enough to discover the thoracic duct, or common trunk of all the lacteals, which conveys the chyle into the subclavian vein. He printed his discovery in the year 1651. And now the lacteals having been traced from the intestines to the thoracic duct, and that duct having been traced to its termination in a blood vessel, the passage of the chyle was completely made out.

The same practice of opening living animals furnished occasions of discovering the lymphatic vessels. This good fortune fell to the lot of Rudbeck first, a young Swedish anatomist; and then to Thomas Bartholin, a Danish anatomist, who was the first who appeared in print upon the lymphatics. His book came out in the year 1653, that is, two years after that of Pecquet. And then it was very evident that they had been seen before by Dr Highmore and others, who had mistaken them for lacteals. But none of the anatomists of those times could make out the origin of the lymphatics, and none of the physiologists could give a satisfactory account of their use.

The circulation of the blood and the passage of the chyle having been satisfactorily traced out in full grown animals, the anatomists were naturally led next to consider how these animal processes were carried on in the child while in the womb of the mother. Accordingly the male and female organs, the appearances and contents of the pregnant uterus, the incubated egg, and every phenomenon which could illustrate generation, became the favourite subject for about 30 years with the principal anatomists of Europe.

Thus it would appear to have been in theory; but Dr Hunter believes, that in fact, as Harvey's master Fabricius laid the foundation for the discovery of the circulation of the blood by teaching him the valves of the veins, and thereby inviting him to consider that subject; so Fabricius, by his lectures, and by his elegant gant work *De Formato Fætui*, et *De Formatione Ovi* et *Pulli*, probably made that likewise a favourite subject with Dr Harvey. But whether he took up the subject of generation in consequence of his discovery of the circulation, or was led to it by his honoured master Fabricius, he spent a great deal of his time in the inquiry; and published his observations in a book *De Generatione Animalium*, in the year 1651, that is, six years before his death.

In a few years after this, Swammerdam, Van Horn, Steno, and D. Graaf, excited great attention to the subject of generation, by their supposed discovery that the females of viviparous animals have ovaria, that is, clusters of eggs in their loins, like oviparous animals; which, when impregnated by the male, are conveyed into the uterus: so that a child is produced from an egg as well as a chick; with this difference that one is hatched within, and the other without, the body of the mother.

Malpighi, a great Italian genius, some time after, made considerable advances upon the subject of generation. He had the good fortune to be the first who used magnifying glasses with address in tracing the first appearances in the formation of animals. He likewise made many other observations and improvements in the minute anatomy by his microscopical labours, and by cultivating comparative anatomy.

This distinguished anatomist gave the first public specimen of his abilities by printing a dissertation on the lungs, anno 1661, a period so remarkable for the study of nature, that it would be injustice to pass it without particular notice.

At the same time flourished Laurentius Bellinus at Florence, and was the first who introduced mathematical reasoning in physic. In 1662, Simon Pauli published a treatise *De Albardis Ossibus*. He had long been admired for the white skeletons he prepared; and at last discovered his method, which was by exposing the bones all winter to the weather.

Johannes Swammerdam of Amsterdam also published some anatomical treatises; but was most remarkable for his knowledge of preserving the parts of bodies entire for many years, by injecting their vessels. He also published a treatise on respiration; wherein he mentioned his having figures of all the parts of the body, as big as the life, cut in copper, which he designed to publish, with a complete system of anatomy. These, however, were never made public by Swammerdam; but, in 1683, Gothofridus Bidloo, professor of anatomy at Leyden, published a work entitled *Anatomia Corporis Humani*, where all the parts were delineated in very large plates almost as big as the life.

Mr Cowper, an English surgeon, bought 300 copies of these figures; and in 1698, published them with an English text, quite different from Bidloo's Latin one; to which were added letters in Bidloo's figures, and some few figures of Mr Cowper's own. To this work Cowper's name was prefixed, without the least mention of Bidloo, except on purpose to confute him. Bidloo immediately published a very ill-natured pamphlet, called *Gulielmus Cowperus citatus corum tribunali*; appealing to the Royal Society, how far Cowper ought to be punished as a plagiary of the worst kind, and endeavouring to prove him an ignorant deceitful fellow. Cowper answered him in his own style, in a pamphlet called his *Vindiciae*; endeavouring to prove, either that Bidloo did not understand his own tables, or that they were none of his. It was even alleged that those were the tables promised by Swammerdam, and which Bidloo had got from his widow. This, however, appears to have been only an invidious surmise, there being unquestionable evidence that they were really the performance of Bidloo.

Soon after, Ibarandus Diembroeck, professor of anatomy at Utrecht, began to appear as an author. His work contained very little original; but he was at great pains to collect from others whatever was valuable in their writings, and his system was the common standard among anatomical students for many years.

About the same time, Antonius Leeuwenhoek of Delft improved considerably on Malpighi's use of microscopes. These two authors took up anatomy where others had dropt it; and, by this new art, they brought a number of amazing things to light. They discovered the red globules of the blood; they were enabled to see the actual circulation of the blood in the transparent parts of living animals, and could measure the velocity of its motion; they discovered that the arteries and veins had no intermediate cells or spongy substance, as Harvey and all the preceding anatomists had supposed, but communicated one with the other by a continuation of the same tube.

Leeuwenhoek was in great fame likewise for his discovery of the animalcula in the semen. Indeed there was scarcely a part of the body, solid or fluid, which escaped his examination; and he almost everywhere found, that what appeared to the naked eye to be rude indigested matter, was in reality a beautiful and regular compound.

After this period, Nuck added to our knowledge of the absorbent system already mentioned, by his injections of the lymphatic glands; Ruysch, by his description of the valves of the lymphatic vessels; and Dr Meckel, by his accurate account of the whole system; and by tracing those vessels in many parts where they had not before been described.

Besides these authors, Drs Hunter and Monro have called the attention of the public to this part of anatomy, in their controversy concerning the discovery of the office of the lymphatics.

When the lymphatic vessels were first seen and traced into the thoracic duct, it was natural for anatomists to suspect, that as the lacteals absorbed from the cavity of the intestines, the lymphatics, which are similar in figure and structure, might possibly do the same office with respect to other parts of the body; and accordingly, Dr Glisson, who wrote in 1654, supposes these vessels arose from cavities, and that their use was to absorb; and Frederic Hoffman has very explicitly laid down the doctrine of the lymphatic vessels being a system of absorbents. But anatomists in general have been of a contrary opinion: for from experiments, particularly such as were made by injections, they have been persuaded that the lymphatic vessels did not arise from cavities, and did not absorb, but were merely continuations from small arteries. The doctrine, therefore, that the lymphatics, like the lacteals, were absorbents, as had been suggested by Glisson and by Hoffman, has been revived by Dr Hunter and Dr Monro, who have controverted the experiments of their predecessors in anatomy, and have endeavoured to prove that the lymphatic vessels are not continued from arteries, but are absorbents.

To this doctrine, however, several objections have been started, particularly by Haller, (Elem. Phys. l. 24. § 2, 3.) and it has been found, that before the doctrine of the lymphatics being a system of absorbents can be established, it must first be determined whether this system is to be found in other animals besides man and quadrupeds. Mr Hewson claims the merit of having proved the affirmative of this question by discovering the lymphatic system in birds, fish, and amphibious animals. See Phil. Trans. vol. lviii. and lixix.—And latterly, Mr Cruikshank has traced the ramifications of that system in almost every part of the body; and from his dissections, figures have been made and lately published to the world. To Mr Sheldon also we are much indebted for his illustration of this system, which promises to give great satisfaction, but of which only a part has been yet published.

The gravid uterus is a subject likewise which has received considerable improvements, particularly relating to one very important discovery; viz. that the internal membrane of the uterus, which Dr Hunter has named decidua, constitutes the exterior part of the secundines or after-birth, and separates from the rest of the uterus every time that a woman either bears a child or suffers a miscarriage. This discovery includes another, to wit, that the placenta is partly made up of an excretion or efflorescence from the uterus itself.

These discoveries are of the utmost consequence, both in the physiological question about the connexion between the mother and child, and likewise in explaining the phenomena of births and abortions, as well as in regulating obstetrical practice.

The anatomists of this century have improved anatomy, and have made the study of it much more easy, by giving us more correct as well as more numerous figures. It is amazing to think of what has been done in that time. We have had four large folio books of figures of the bones, viz. Cheselden's, Albinius's, Sue's and Trew's. Of the muscles, we have had two large folios; one from Cowper, which is elegant; and one from Albinius, which, from the accuracy and labour of the work, we may suppose will never be outdone. Of the blood vessels we have a large folio from Dr Haller. We have had one upon the nerves from Dr Meckel, and another by Dr Monro junior. We have had Albinius's, Roederer's, Jentyl's, and Hunter's works upon the pregnant uterus; Weitbrecht and Leber on the joints and fresh bones; Soemerring on the brain; Zinn on the eye; Cotunnius, Meckel junior, &c. on the ear; Walter on the nerves of the thorax and abdomen; Dr Monro on the bursae mucosae, &c.

It would be endless to mention the anatomical figures that have been published in this century of particular and smaller parts of the body, by Morgagni, Ruysch, Valsalva, Sanctorini, Heister, Vater, Cant, Zimmerman, Walterus, and others.

Those elegant plates of the brain, however, just published by M. Vicq. d'Azyr, must not pass without notice, especially as they form part of an universal system of anatomy and physiology, both human and comparative, proposed to be executed in the same splendid style. Upon the brain alone 19 folio plates are employed; of which several are coloured. The figures are delineated with accuracy and clearness; but the colouring is rather beautiful than correct. Such parts of this work as may be published, cannot fail to be equally acceptable to the anatomist and the philosopher; but the entire design is apparently too extensive to be accomplished within the period of a single life. In our own country, also, a very great anatomical work is carrying on by Andrew Bell, F.S.A.S. engraver to his Royal Highness the Prince of Wales, with the approbation of Dr Monro, and under the inspection of his very ingenious assistant Mr Fyfe. It is to compose a complete illustration, both general and particular, of the human body, by a selection from the best plates of all the greatest anatomists, as well foreign as of this country, exhibiting the latest discoveries in the science, and accompanied with copious explanations. The whole number of plates mentioned in the Prospectus is 240, of which 152 are already done; all in royal folio.

To the foreign treatises already mentioned may be added those recently published by Sabbatier and Plenck on anatomy in general. Among ourselves, the writings of Keil, Douglas, Cheselden, the first Monro, Winslow, &c. are too well known to need description. The last of these used to be recommended as a standard for the students of anatomy; but it has of late given place to a more accurate and comprehensive system, in three volumes, published by Mr Elliot of Edinburgh, upon a plan approved of by Dr Monro, and executed by Mr Fyfe. Dr Simmons of London has also obliged the world with an excellent system of anatomy; and another work under the title of "Elements of Anatomy and the Animal Economy;" in which the subjects are treated with uncommon elegance and perspicuity.

In the latter part of the last century, anatomy made two great steps, by the invention of injections, and the method of making what we commonly call preparations. These two modern arts have really been of infinite use to anatomy; and besides have introduced an elegance into our administrations, which in former times could not have been supposed to be possible. They arose in Holland under Swammerdam and Ruysch, and afterwards in England under Cowper, St André, and others, where they have been greatly improved.

The anatomists of former ages had no other knowledge of the blood vessels than what they were able to collect from laborious dissections, and from examining the smaller branches of them, upon some lucky occasion, when they were found more than commonly loaded with red blood. But filling the vascular system with a bright coloured wax, enables us to trace the large vessels with great ease, renders the smaller much more conspicuous, and makes thousands of the very minute ones visible, which from their delicacy, and the transparency of their natural contents, are otherwise imperceptible.

The modern art of corroding the fleshy parts with a menstruum, and of leaving the moulded wax entire, is so exceedingly useful, and at the same time so ornamental, that it does great honour to the ingenious inventor Dr Nicholls.

The wax-work arts of the moderns might deserve notice in any history of anatomy, if the masters in that way had not been so careless in their imitation. Many of the wax figures are so tawdry, with a show of unnatural colours, and so very incorrect in the circumstances of The human body has been commonly known by the name Microcosmus, or the little world; as if it did not differ so much from the universal system of nature in the symmetry and number of its parts as in their size.

Galen's excellent treatise De Usu Partium, was composed as a prose hymn to the Creator; and abounds with irresistible proofs of a supreme Cause and governing Providence, as we find in modern physico-theology. And Cicero dwells more on the structure and economy of animals than on all the productions of nature besides, when he wants to prove the existence of the gods from the order and beauty of the universe. He there takes a survey of the body of man in a most elegant synopsis of anatomy; and concludes thus: "Quibus rebus expositis, satis docuisse videor, hominis natura, quanto omnes anterier animantes. Ex quo debet intelligi, nec figuram situmque membrorum, nec ingenii mentisque vim talem effici potuisse fortuna."

The satisfaction of mind which arises from the study of anatomy, and the influence which it must naturally have upon our minds as philosophers, cannot be better conveyed than by the following passage from the same author: "Quae contuens animas, accepit ab his cognitionem deorum, ex qua ortur pretas: cui conjuncta justitia est, reliquaque virtutes: ex quibus vita beata, existit, par et similis deorum, nulla alia re nisi immortalitate, quae nihil ad bene vivendum pertinet, sedesse celestibus."

It would be endless to quote the animated passages of this sort which are to be found in the physicians, philosophers, and theologians, who have considered the structure and functions of animals with a view towards the Creator. It is a view which must strike one with a most awful conviction. Who can know and consider the thousand evident proofs of the astonishing art of the Creator, in forming and sustaining an animal body such as ours, without feeling the most pleasant enthusiasm? Can we seriously reflect upon this awful subject, without being almost lost in adoration? without longing for another life after this, in which we may be gratified with the highest enjoyment which our faculties and nature seem capable of, the seeing and comprehending the whole plan of the Creator, in forming the universe and in directing all its operations?

But the more immediate purposes of anatomy concern those who are to be the guardians of health, as this study is necessary to lay a foundation for all the branches of medicine. The more we know of our fabric, the more reason we have to believe, that if our senses were more acute, and our judgment more enlarged, we should be able to trace many springs of life which are now hidden from us: by the same sagacity we should discover the true causes and nature of diseases; and thereby be enabled to restore the health of many, who are now, from our more confined knowledge, said to labour under incurable disorders. By such an intimate acquaintance with the economy of our bodies, we should discover even the seeds of diseases, and destroy them before they had taken root in the constitution.

That anatomy is the very basis of surgery every body allows. It is dissection alone that can teach us, where we may cut the living body with freedom and dispatch; and where we may venture with great circumspection and General and delicacy; and where we must not upon any account attempt it. This informs the head, gives dexterity to the hand, and familiarizes the heart with a sort of necessary inhumanity, the use of cutting instruments upon our fellow-creatures.

Besides the knowledge of our body, through all the variety of its structure and operations in a sound state, it is by anatomy only that we can arrive at the knowledge of the true nature of most of the diseases which afflict humanity. The symptoms of many disorders are often equivocal; and diseases themselves are thence frequently mistaken, even by sensible, experienced, and attentive physicians. But by anatomical examination after death, we can with certainty find out the mistake, and learn to avoid it in any similar case.

This use of anatomy has been so generally adopted by the moderns, that the cases already published are almost innumerable: Mangetus, Morgagni, indeed many of the best modern writings in physic, are full of them. And if we look among the physicians of the best character, and observe those who have the art itself, rather than the craft of the profession at heart; we shall find them constantly taking pains to procure leave to examine the bodies of their patients after death.

After having considered the rise and progress of anatomy; the various discoveries that have been made in it, from time to time; the great number of diligent observers who have applied themselves to this art; and the importance of the study, not only for the prevention and cure of diseases, but in furnishing the liveliest proofs of divine wisdom; the following questions seem naturally to arise: For what purposes is there such a variety of parts in the human body? Why such a complication of nice and tender machinery? Why was there not rather a more simple, less delicate, and less expensive frame (a)?

In order to acquire a satisfactory general idea of this subject, and find a solution of all such questions, let us, in our imagination, make a man: in other words, let us suppose that the mind, or immaterial part, is to be placed in a corporeal fabric, in order to hold a correspondence with other material beings by the intervention of the body; and then consider, a priori, what will be wanted for her accommodation. In this inquiry, we shall plainly see the necessity or advantage, and therefore the final cause, of most of the parts which we actually find in the human body. And if we consider that, in order to answer some of the requisites, human wit and invention would be very insufficient; we need not be surprised if we meet with some parts of the body whose use we cannot yet perceive, and with some operations or functions which we cannot explain. We can see that the whole bears the most striking characters of excelling wisdom and ingenuity: but the imperfect senses and capacity of man cannot pretend to reach every part of a machine, which nothing less than the intelligence and power of the Supreme Being could contrive and execute.

First, then, The mind, the thinking immaterial agent, must be provided with a place of immediate residence, which shall have all the requisites for the union of spirit and body; accordingly she is provided with the brain, where she dwells as governor and superintendant of the whole fabric.

In the next place, As she is to hold a correspondence with all the material beings around her, she must be supplied with organs fitted to receive the different kinds of impressions which they will make. In fact, therefore, we see that she is provided with the organs of sense, as we call them; the eye is adapted to light; the ear to sound; the nose to smell; the mouth to taste; and the skin to touch.

Further: She must be furnished with organs of communication between herself in the brain and those organs of sense, to give her information of all the impressions that are made upon them: and she must have organs between herself in the brain and every other part of the body, fitted to convey her commands and influence over the whole. For these purposes the nerves are actually given. They are chords, which rise from the brain, the immediate residence of the mind, and disperse themselves in branches through all parts of the body. They convey all the different kinds of sensations to the mind, in the brain; and likewise carry out from thence all her commands or influence to the other parts of the body. They are intended to be occasional monitors against all such impressions as might endanger the wellbeing of the whole, or of any particular part; which vindicates the Creator of all things, in having actually subjected us to those many disagreeable and painful sensations which we are exposed to from a thousand accidents in life.

Moreover, the mind, in this corporeal system, must be endued with the power of moving from place to place, that she may have intercourse with a variety of objects; that she may fly from such as are disagreeable, dangerous, or hurtful, and pursue such as are pleasant or useful to her. And accordingly she is furnished with limbs, and with muscles and tendons, the instruments of motion, which are found in every part of the fabric where motion is necessary.

But to support, to give firmness and shape to the fabric; to keep the softer parts in their proper places; to give fixed points for, and the proper direction to its motions as well as to protect some of the more important and tender organs from external injuries; there must be some firm prop-work interwoven through the whole. And in fact, for such purposes the bones are given.

The prop-work must not be made into one rigid fabric, for that would prevent motion. Therefore there are a number of bones.

These pieces must all be firmly bound together, to prevent their dislocation. And this end is perfectly well answered by the ligaments.

The extremities of these bony pieces, where they move and rub upon one another, must have smooth and slippery surfaces for easy motion. This is most happily provided for by the cartilages and mucous of the joints.

(a) The following beautiful representation is taken from the late Dr Hunter's Introductory Lecture on Anatomy. The interstices of all these parts must be filled up with some soft and ductile matter, which shall keep them in their places, unite them, and at the same time allow them to move a little upon one another. And these purposes are answered by the cellular membrane or adipose substance.

There must be an outward covering over the whole apparatus, both to give it compactness and to defend it from a thousand injuries; which, in fact, are the very purposes of the skin and other integuments.

Lastly, The mind being formed for society and intercourse with beings of her own kind, she must be endued with powers of expressing and communicating her thoughts by some sensible marks or signs; which shall be both easy to herself, and admit of great variety: and accordingly she is provided with the organs and faculty of speech, by which she can throw out signs with amazing facility, and vary them without end.

Thus we have built up an animal body which would seem to be pretty complete: but as it is the nature of matter to be altered and worked upon by matter; so in a very little time such a living creature must be destroyed, if there is no provision for repairing the injuries which she must commit upon herself, and those which she must be exposed to from without. Therefore a treasure of blood is actually provided in the heart and vascular system, full of nutritious and healing particles, fluid enough to penetrate into the minutest parts of the animal; impelled by the heart, and conveyed by the arteries, it washes every part, builds up what was broken down, and sweeps away the old and useless materials. Hence we see the necessity or advantage of the heart and arterial system.

What more there was of this blood than enough to repair the present damages of the machine, must not be lost, but should be returned again to the heart; and for this purpose the venous system is actually provided.

These requisites in the animal explain, *a priori*, the circulation of the blood.

The old materials which were become useless, and are swept off by the current of blood, must be separated and thrown out of the system. Therefore glands, the organs of secretion, are given for straining whatever is redundant, vapid, or noxious, from the mass of blood; and when strained, they are thrown out by emunctories, called organs of excretion.

But now, as the machine must be constantly wearing, the reparation must be carried on without intermission, and the strainers must always be employed. Therefore there is actually a perpetual circulation of the blood, and the secretions are always going on.

Even all this provision, however, would not be sufficient; for that store of blood would soon be consumed, and the fabric would break down, if there were not a provision made for fresh supplies. These we observe, in fact, are profusely scattered round her in the animal and vegetable kingdoms; and she is furnished with hands, the fittest instruments that could have been contrived, for gathering them, and for preparing them in a variety of ways for the mouth.

But these supplies, which we call food, must be considerably changed; they must be converted into blood. Therefore she is provided with teeth for cutting and bruising the food, and with a stomach for melting it down: In short, with all the organs subservient to digestion. The finer parts of the aliment only can be useful in the constitution; these must be taken up and conveyed into the blood, and the dregs must be thrown off. With this view the intestinal canal is actually given. It separates the nutritious part, which we call chyle, to be conveyed into the blood by the system of absorbent vessels; and the feces pass downwards, to be conducted out of the body.

Now we have got our animal not only furnished with what is wanted for its immediate existence, but also with the powers of protracting that existence to an indefinite length of time. But its duration, we may presume, must necessarily be limited: for as it is nourished, grows, and is raised up to its full strength and utmost perfection; so it must in time, in common with all material beings, begin to decay, and then hurry on to final ruin. Hence we see the necessity of a scheme for renovation. Accordingly wise Providence, to perpetuate as well as to preserve his work, besides giving a strong appetite for life and self-preservation, has made animals male and female, and given them such organs and passions as will secure the propagation of the species to the end of time.

Thus we see, that, by the very imperfect survey which human reason is able to take of this subject, the animal man must necessarily be complex in his corporeal system, and in its operations.

He must have one great and general system, the vascular, branching through the whole for circulation: Another, the nervous, with its appendages the organs of sense, for every kind of feeling: And a third, for the union and connexion of all those parts.

Besides these primary and general systems, he requires others which may be more local or confined: One for strength, support, and protection; the bony compasses: Another for the requisite motions of the parts among themselves, as well as for moving from place to place; the muscular part of the body: Another to prepare nourishment for the daily recruit of the body; the digestive organs: and one for propagating the species; the organs of generation.

And in taking this general survey of what would appear, *a priori*, to be necessary for adapting an animal to the situations of life, we observe, with great satisfaction, that man is accordingly made of such systems, and for such purposes. He has them all; and he has nothing more except the organs of respiration. Breathing it seemed difficult to account for *a priori*: we only knew it to be in fact essential and necessary to life. Notwithstanding this, when we saw all the other parts of the body, and their functions, so well accounted for, and so wisely adapted to their several purposes, there could be no doubt that respiration was so likewise: And accordingly, the discoveries of Dr Priestley have lately thrown light upon this function also, as will be shown in its proper place.

Of all the different systems in the human body, the use and necessity are not more apparent, than the wisdom and contrivance which has been exerted in putting them all into the most compact and convenient form: in disposing them so, that they shall mutually receive and give helps to one another; and that all, or many of the parts, shall not only answer their principal end or purpose, but operate successfully and usefully in a variety of secondary ways. If we consider the whole animal machine in this light, and compare it with any machine in which human art has exerted its utmost, suppose the best constructed ship that ever was built, we shall be convinced beyond the possibility of doubt, that there are intelligence and power far surpassing what humanity can boast of.

One superiority in the natural machine is peculiarly striking. In machines of human contrivance or art, there is no internal power, no principle in the machine itself, by which it can alter and accommodate itself to any injury which it may suffer, or make up any injury which admits of repair. But in the natural machine, the animal body, this is most wonderfully provided for, by internal powers in the machine itself; many of which are not more certain and obvious in their effects, than they are above all human comprehension as to the manner and means of their operation. Thus, a wound heals up of itself; a broken bone is made firm again by a callus; a dead part is separated and thrown off; noxious juices are driven out by some of the emunctories; a redundancy is removed by some spontaneous bleeding; a bleeding naturally stops of itself; and a great loss of blood, from any cause, is in some measure compensated by a contracting power in the vascular system, which accommodates the capacity of the vessels to the quantity contained. The stomach gives information when the supplies have been expended; represents, with great exactness, the quantity and the quality of what is wanted in the present state of the machine; and in proportion as she meets with neglect, rises in her demand, urges her petition in a louder tone, and with more forcible arguments. For its protection, an animal body resists heat and cold in a very wonderful manner, and preserves an equal temperature in a burning and in a freezing atmosphere.

A further excellence and superiority in the natural machine, if possible, still more astonishing, more beyond all human comprehension, than what we have been speaking of, is the following: Besides those internal powers of self-preservation in each individual, when two of them co-operate, or act in concert, they are endowed with powers of making other animals, or machines, like themselves, which again are possessed of the same powers of producing others, and so of multiplying the species without end.

These are powers which mock all human invention or imitation. They are characteristics of the divine Architect.

Having premised this general account of the subject, we shall next consider the method to be observed in treating it.

Anatomy, it has been already observed, is divided into two parts; Anatomy, properly so called, or the anatomy of the human body, and Comparative Anatomy. In the following treatise we shall adopt the same arrangement. In the first part we shall treat of the Anatomy of the Human Body, and in the second of Comparative Anatomy.

PART I.

ANATOMY OF THE HUMAN BODY.

The study of the human body, as already noticed, is commonly divided into two parts. The first, which is called Anatomy, relates to the matter and structure of its parts; the second, called Physiology and animal economy, relates to the principles and laws of its internal operations and functions.

As the body is a compound of solids and fluids, Anatomy is divided into,

1. The Anatomy of the solids, and 2. The Anatomy of the fluids.

1. The solids, by which we mean all parts of our body which are not fluid, are generally divided into two classes, viz.

1. The hard solids or bones. This part of anatomy is called Osteology; which signifies the doctrine of the bones.

2. The softer solids; which part is called Sarcology, viz. the doctrine of the flesh.

This division of the solids, we may observe, has probably taken its origin from the vulgar observation, that the body is made of bone and flesh. And as there are many different kinds of what are called soft or fleshy parts, Sarcology is subdivided into,

(1.) Angiology, or the doctrine of vessels; by which is commonly understood blood vessels; (2.) Adenology, of glands; (3.) Neurology, of nerves; (4.) Mycology, of muscles; and, (5.) Splanchnology, of the viscera or bowels. There is, besides, that part which treats of the organs of sense and of the integuments.

This division of the solids has been here mentioned, rather for the sake of explaining so many words, which are constantly used by anatomists, than for its importance or accuracy. For besides many other objections that might be urged, there are in the body three species of solids, viz. gristle or cartilage, hair, and nails; which are of an intermediate nature between bone and flesh; and therefore cannot so properly be brought into the osteology or the sarcology. The cartilages were classed with the bones; because the greatest number of them are appendages to bones; and for the like reason the hair and the nails were classed with the integuments.

II. The fluids of the human body may be divided into three kinds, which Dr Hunter calls the crude, the general or perfect, and the local or secreted fluid.

1. By the crude fluid is meant the chyle, and whatever is absorbed at the surfaces of the body; in other words, what is recently taken into the body, and is not yet mixed with or converted into blood.

2. The general or perfect fluid is the blood itself; viz. what is contained in the heart, arteries, and veins, and is going on in the round of the circulation. 3. The local or secreted, are those fluids peculiar to particular parts of the body, which are strained off from the blood, and yet are very different in their properties from the blood. They are commonly called secretions; and some are useful, others excrementitious.

In treating of the Physiology, it is very difficult to say what plan should be followed; for every method which has been yet proposed is attended with manifest inconvenience. The powers and operations of the machine have such a dependence upon one another, such connexions and reciprocal influence, that they cannot well be understood or explained separately. In this sense our body may be compared to a circular chain of powers, in which nothing is first or last, nothing so-

litary or independent; so that whenever we begin, we find that there is something preceding which we ought to have known. If we begin with the brain and the nerves, for example, we shall find that these cannot exist, even in idea, without the heart: if we set out with the heart and vascular system, we shall presently be sensible that the brain and the nerves must be supposed: or, should we take up the mouth, and follow the course of the aliment, we should see that the very first organ which presented itself, supposed the existence both of the heart and brain: Wherefore we shall incorporate the Physiology with the Anatomy, by attempting to explain the functions after we have demonstrated the organs.

CHAP. I. OSTEOLoGY.

WE begin with the bones, which may be considered as the great support of the body, tending to give it shape and firmness.—But before we enter into the detail of each particular bone, it will be necessary to describe their composition and connexions, and to explain the nature of the different parts which have an immediate relation to them: as the cartilages, ligaments, periosteum, marrow, and synovial glands.

Sect. I. Of the Bones in general, with their Appendages, &c.

The bones are of a firm and hard (b) substance, of a white colour, and perfectly insensible. They are the most compact and solid parts of the body, and serve for the attachment or support of all the other parts.

Three different substances are usually distinguished in them; their exterior or bony part, properly so called; their spongy cells; and their reticular substance. The first of these is formed of many laminae or plates, composing a firm hard substance.—The spongy or cellular part is so called on account of its resemblance to a sponge, from the little cells which compose it. This substance forms almost the whole of the extremities of cylindrical bones. The reticular part is composed of fibres, which cross each other in different directions. This net-work forms the internal surface of those bones which have cavities.

The flat bones, as those of the head, are composed only of the laminae and the cellular substance. This last is usually found in the middle of the bone, dividing it into two plates, and is there called diploe.

Gagliardi, who pretended to have discovered an infinite number of claviculi (c) or bony processes, which he describes as traversing the laminae to unite them together, has endeavoured to support this pretended discovery by the analogy of bones to the bark of trees, in which certain woody nails have been remarked; but this opinion seems to be altogether fanciful.

Some writers have supposed, that the bones are formed by layers of the periosteum, which gradually ossify in the same manner as the timber is formed in trees by the hardening of the white substance that is found between the inner bark and the wood. M. Dubamel, who has adopted this opinion, fed different animals with madder and their ordinary food alternately during a certain time; and he asserts, that in dissecting their bones, he constantly observed distinct layers of red and white, which corresponded with the length of time they had lived on madder or their usual aliment. But it has since been proved by Detleff, that M. Dubamel's experiments were inaccurate, and that neither the periosteum nor the cartilages are tinged by the use of madder, which is known to affect the bones only.

We usually consider in a bone, its body and its extremities. The ancients gave the name of diaphysis to the body or middle part, and divided the extremities into apophysis and epiphysis. An apophysis, or process, as it is more commonly called, is an eminence continued from the body of the bone, whereas an epiphysis is at first a sort of an appendage to the bone by means of an intermediate cartilage. Many epiphyses, which appear as distinct bones in the fetus, afterwards become apophyses; for they are at length so completely united to the body of the bone as not to be distinguishable from it in the adult state. It is not unusual, however, at the age of 18 and even 20 years, to find the extremities of bones still in the state of epiphyses.

The names given to the processes of bones are expressive of their shape, size, or use; thus if a process is large and of a spherical form, it is called capitul or head; if the head is flatted, it is termed condyle. Some processes, from their resemblance to a stiletto, a breast, or the beak of a crow, are called styloid, mastoid or coracoid; others are styled ridges or spines. The two processes of the os femoris derive their name of trochanters from their use.

A bone has its cavities as well as processes. These cavities

(b) Mr Scheele discovered that bones contain the phosphoric acid united with calcareous earth; and that to this combination they owe their firmness.

(c) In his Anat. ossium nov. invent. illustrat. he describes four kinds of these claviculi or nails, viz. the perpendicular, oblique, headed, and crooked. cavities either extend quite through its substance, or appear only as depressions. The former are called foramina or holes, and these foramina are sometimes termed canals or conduits, according to their form and extent. Of the depressions, some are useful in articulation. These are called cotyloid when they are deep, as is the case with the os innominatum, where it receives the head of the os femoris; or glenoid when they are superficial, as in the scapula, where it receives the os humeri. Of the depressions that are not designed for articulation, those which have small apertures are called sinuses; others that are large, and not equally surrounded by high brims, are styled fossae; such as are long and narrow, furrows; or if broad and superficial without brims, sinuositics. Some are called digital impressions, from their resemblance to the traces of a finger on soft bodies.

We shall abridge this article, which is exceedingly diffuse in the generality of anatomical books, and will endeavour to describe it with all the clearness it will allow.

The bones composing the skeleton are so constructed, that the end of every bone is perfectly adapted to the extremity of that with which it is connected, and this connexion forms what is called their articulation.

Articulation is divided into diarthrosis, synarthrosis, and amphiarthrosis, or moveable, immoveable, and mixed articulation. Each of the two first has its subdivisions. Thus the diarthrosis, or moveable articulation, includes, 1. The enarthrosis, as it is called, when a large head is admitted into a deep cavity, as in the articulation of the os femoris with the os innominatum. 2. Arthrodia, when a round head is articulated with a superficial cavity, as is the case of the os humeri and scapula. 3. Ginglimus, or hinge-like articulation, as in the connexion of the thigh-bone with the tibia. The enarthrosis and arthrodia allow of motion to all sides; the ginglimus only of flexion and extension.

The synarthrosis, or immoveable articulation, includes, 1. The suture, when the two bones are indented into each other, as is the case with the parietal bones. 2. Gomphosis, when one bone is fixed into another, in the manner the teeth are placed in their sockets.

The term amphiarthrosis is applied to those articulations which partake both of the synarthrosis and diarthrosis, as is the case with the bones of the vertebre, which are capable of motion in a certain degree, although they are firmly connected together by intermediate cartilages.

What is called symphyses is the union of two bones into one; as in the lower jaw, for instance, which in the fetus consists of two distinct bones, but becomes one in a more advanced age, by the ossification of the uniting cartilage.

When bones are thus joined by the means of cartilages, the union is styled synchondrosis; when by ligaments, syndesmosis.

Cartilages are white, solid, smooth, and elastic substances, between the hardness of bones and ligaments, and seemingly of a fibrous texture. We are not able to trace any vessels into their substance by injection, nor are they ever found tinged in animals that have been fed with madder.

They may be distinguished into, 1st, Those which are connected with the bones; and 2dly, Those which belong to other parts of the body. The first serve either to cover the ends and cavities of bones intended for motion, as in the articulations, where by their smoothness they facilitate motions, which the bones alone could not execute with so much freedom; or, they serve to unite bones together, as in the symphyysis pubis, or to lengthen them as in the ribs.

Many of them ossifying as we advance in life, their number is less in the adult than in the fetus, and of course there are fewer bones in the old than in the young subject.

Of the second class of cartilages, or those belonging to the soft parts, we have instances in the larynx, where we find them useful in the formation of the voice, and for the attachment of muscles.

The periosteum is a fine membrane of a compact cellular texture, reflected from one joint to another, serving as a common covering to the bones. It has sanguiferous and lymphatic vessels, and is supplied with nerves from the neighbouring parts. It adheres very firmly to their surface, and by its smoothness facilitates the motion of muscles. It likewise supports the vessels that go to be distributed through the substance of the bones, and may serve to strengthen the articulations. At the extremities of bones, where it is found covering a cartilage, it has by some been improperly considered as a distinct membrane, and named perichondrium. This, in its use and structure, resembles the periosteum. Where it covers the bones of the skull, it has gotten the name of pericranium.

The periosteum is not a production of the dura mater, as the ancients, and after them Havers, imagined; nor are the bones formed by the ossification of this membrane, at least when it is in a sound state, as some late writers have supposed.

The periosteum is deficient in the teeth above the sockets, and in those parts of bones to which ligaments or tendons are attached.

The marrow is a fat oily substance, filling the cavities of bones. In the great cavities of long bones it is of a much firmer consistence than in the cells of their spongy part. In the former it inclines somewhat to a yellowish tinge, and is of the consistence of fat; in the latter it is more fluid, and of a red colour. This difference in colour and consistence is owing to accidental causes; both kinds are of the same nature, and may both be described under the common name of marrow, though some writers give this name only to the fat-like substance, and call the other the medullary juice.

The marrow is contained in a very fine and transparent membrane, which is supplied with a great number of blood vessels, chiefly from the periosteum. This membrana medullaris adheres to the inner surface of the bones, and furnishes an infinite number of minute bags or vesicles for enclosing the marrow, which is likewise supported in the cavities of the bones by the long filaments of their reticular substance.

Besides the vessels from the periosteum, the membrana medullaris is furnished with others, which in the long bones may be seen passing in near the extremities of the bone, and sending off numerous branches that ramify through all the vesicles of this membrane.

The bones, and the cells containing the marrow, are likewise furnished with lymphatics. By their means, the marrow, like the fat, may be taken up in a greater quantity than it is secreted; and hence it is that so little is found in the bones of those who die of lingering diseases.

It is still a matter of controversy, Whether the marrow is sensible or not? We are certainly not able to trace any nerves to it; and from this circumstance, and its analogy to fat, Haller has ventured to consider it as insensible. On the other hand, Duverney asserts, that an injury done to this substance in a living animal was attended with great pain. In this dispute physiologists do not seem to have sufficiently discriminated between the marrow itself and the membranous cells in which it is contained. The former, like the fat, being nothing more than a secreted, and of course an inorganized matter, may, with propriety, be ranked among the insensible parts, as much as inspissated mucus or any other secreted matter in the body; whereas the membrana medullaris being vascular, though it possesses but an obscure degree of feeling in a sound state, is not perfectly insensible.

The marrow was formerly supposed to be intended for the nourishment and renewal of the bones; but this doctrine is now pretty generally and deservedly exploded. It seems probable that the marrow is to the bones what fat is to the soft parts. They both serve for some important purposes in the animal economy; but their particular use has never yet been clearly ascertained. The marrow, from the transudation of the oil through the bones of a skeleton, is supposed to diminish their brittleness; and Havers, who has written professedly on the bones, describes the canals by which the marrow is conveyed through every part of their substance, and divides them into longitudinal and transverse ones. He speaks of the first as extending through the whole length of the bone; and of the latter, as the passages by which the longitudinal ones communicate with each other. The similarity of these to the large cancelli in burnt bones, and the transudation of the oil through the bones of the skeleton, seems to prove that some such passages do actually exist.

The synovial glands are small bodies (D), supposed to be of a glandular structure, and exceedingly vascular, secreting a fluid of a clear mucilaginous nature, which serves to lubricate the joints. They are placed in small cavities in the articulations, so as to be capable of being gently compressed by the motion of the joint, which expresses their juice in proportion to the degree of friction. When the synovia is wanting, or is of too thick a consistence, the joint becomes stiff and incapable of flexion or extension. This is what is termed ankylosis.

Ligaments are white, glistening, inelastic bands, of a compact substance, more or less broad or thick, and serving to connect the bones together. They are distinguished by different names adapted to their different forms and uses. Those of the joints are called either round or bursal. The round ligaments are white, tendinous and inelastic. They are strong and flexible, and are found only in the joint of the knee, and in the articulation of the os femoris with the os innominatum. The bursal or capsular ligaments surround the whole joint like a purse, and are to be found in the articulations which allow motion every way, as in the articulation of the arm with the scapula.

Of those sacs called Bursae Mucosæ, a few were known to former anatomists, but by much the greater number have been since discovered by Dr Monro (E), who observes, that they are to be met with in the extremities of the body only; that many of them are placed entirely on the inner sides of the tendons, between these and the bones. Many others cover not only the inner, but the outer sides of the tendons, or are interposed between the tendons and external parts, as well as between those and the bones.

Some are situated between the tendons and external parts only or chiefly, some between contiguous tendons, or between the tendons or the ligaments and the joints. A few such sacs are observed where the processes of bones play upon the ligaments, or where one bone plays upon another. Where two or more tendons are contiguous, and afterwards separate from each other, we generally find a common bursa divided into branches with which it communicates; and a few bursae of contiguous tendons communicate with each other.—Some, in healthy children, communicate with the cavities of the joints; and in many old people he has seen such communication formed by use or worn by friction, independent of disease.

Their proper membrane is thin and transparent, but very dense, and capable of confining air or any other fluid. It is joined to the neighbouring parts by the common cellular substance. Between the bursa and the hard substance of bone a thin layer of cartilage or of tough membrane is very generally interposed. To the cellular substance on the outside of the bursa, the adipose substance is connected: except where the bursa covers a tendon, cartilage, or bone, much exposed to pressure or friction.

In several places a mass of fat, covered with the continuation of the membrane of the bursa, projects into its cavity. The edges of this are divided into fringes.

The inner side of the membrane is smooth, and is extremely slippery from the liquor secreted in it.

The structure of the bursa bears a strong resemblance to the capsular ligaments of the joints. 1. The inner layer of the ligament, like that of the bursa, is thin and dense. 2. It is connected to the external ligaments by the common cellular substance. 3. Between it and the bones, layers of cartilage, or the articular cartilage, are interposed. 4. At the sides of the joints, where it is not subject to violent pressure and friction, the adipose substance is connected with the cellular membrane. 5. Within the cavities of the joints we observe masses of fat projecting, covered with similar blood-vessels, and with similar fimbriae hanging from their

(D) It is now much doubted, however, whether the appearances in the joints, which are usually called glands, are any thing more than assemblages of fat.

(E) See Description of the Bursae Mucosæ, &c. In the knee the upper part of such a mass of fat forms what has been called the mucilaginous gland of the joint, and the under part projects into the bursa behind the ligament which ties the patella to the tibia. 7. The liquor which lubricates the bursa has the same colour, consistence, and properties, as that of the joints, and both are affected in the same manner by heat, mineral acids, and ardent spirits. 8. In some places the bursae constantly communicate with the cavities of the joints, in others they generally do so; from which we may infer a sameness of structure.

When we examine the fimbriae common to the fatty bodies of the joints and bursae, and which have been supposed to be the ducts of glands lodged within the masses of fat, we are not able to discover any glandular appearance within them. And although we observe many vessels dispersed upon the membranes of the fatty bodies and fimbriae; and that we cannot doubt that these fimbriae consist of ducts which contain a lubricating liquor, and can even press such a liquor from them; yet their cavities and orifices are so minute, that they are not discoverable even by the assistance of magnifying glasses. These fimbriae appear, therefore, to be ducts like those of the urethra, which prepare a mucilaginous liquor without the assistance of any knotty or glandular organ.

Upon the whole, the synovia seems to be furnished by invisible exhalent arteries, by the ducts of the fimbriae, and by oil exuding from the adipose follicles by passages not yet discovered.

The word skeleton, which by its etymology implies simply a dry preparation, is usually applied to an assemblage of all the bones of an animal united together in their natural order. It is said to be a natural skeleton, when the bones are connected together by their own proper ligaments; and an artificial one, when they are joined by any other substance, as wire, &c.

The skeleton is generally divided into the head, trunk, and extremities. The first division includes the bones of the cranium and face. The bones of the trunk are the spine, ribs, sternum, and bones of the pelvis.

The upper extremity on each side consists of the two bones of the shoulder, viz. the scapula and clavicle; the bone of the arm or os humeri; the bones of the forearm, and those of the hand.

The lower extremity on each side of the trunk consists of the thigh-bone and the bones of the leg and foot.

Sect. II. Of the Bones of the Head.

The head is of a roundish figure, and somewhat oval (F). Its greatest diameter is from the forehead to the occiput; its upper part is called vertex, or crown of the head; its anterior or fore-part the face; and the upper part of this, sinciput, or forehead; its sides the temples; its posterior, or hind part, the occiput; and its inferior part the basis.

The bones of the head may be divided into those of the cranium and face.

§ I. Bones of the Cranium and Face.

There are eight bones of the cranium, viz. the coronal bone or os frontis; the two parietal bones or ossa bregmati; the os occipitis; the two temporal bones; the sphenoid bone; and the os ethmoides or cribriforme.

Of these, only the os occipitis and ossa bregmati are considered as proper to the cranium; the rest being common both to the cranium and face.

These bones are all harder at their surface than in their middle: and on this account they are divided into two tables, and a middle spongy substance called diploe.

In this, as in all the other bones, we shall consider its figure, structure, processes, depressions, and cavities; and the manner in which it is articulated with the other bones.

The os frontis has some resemblance in shape to the shell of the cockle. Externally it is convex, its concave side being turned towards the brain. This bone, in the places where it is united to the temporal bones, is very thin, and has there no diploe. It is likewise exceedingly thin in that part of the orbit of the eye which is nearest to the nose. Hence it is, that a wound in the eye, by a sword, or any other pointed instrument, is sometimes productive of immediate death. In these cases, the sword passing through the weak part of the bone, penetrates the brain, and divides the nerves at their origin; or perhaps opens some blood-vessel, the consequences of which are soon fatal.

We observe on the exterior surface of this bone five apophyses or processes, which are easily to be distinguished. One of these is placed at the bottom and narrowest part of the bone, and is called the nasal process, from its supporting the upper end of the bones of the nose. The four others are called angular or orbital processes. They assist to form the orbits, which are the cavities on which the eyes are placed. In each of these orbits there are two processes, one at the interior or great angle, and the other at the exterior or little angle of the orbit. They are called the angular processes. Between these a ridge is extended in form of an arch, and on this the eyebrows are placed. It is called the orbital or superciliary ridge, and in some measure covers and defends the globe of the eye. There is a hole in this for the passage of the frontal vessels and nerves. This arch is interrupted near the nose by a small pit, in which the tendon of the musculus obliquus major of the eye is fixed. From the under part of each superciliary ridge a thin plate runs a considerable way backwards, and has the name of orbital; the external and fore part of this plate forms

(‡) The bones of the fetus being perfectly distinct, and the muscles in young persons not acting much, the shape of the head has been supposed to depend much on the management of children when very young. Vesalius, who has remarked the difference in people of different nations, observes, for instance, that the head of a Turk is conical, from the early use of the turban; whilst that of an Englishman is flattened by the chin-stay. Some of the latest physiologists suppose, with good reason, that this difference is chiefly owing to certain natural causes with which we are as yet unacquainted. forms a sinusosity for lodging the lacrimal gland. Between the orbital plates there is a large discontinuation of the bone, which is filled up by the cribriform part of the os ethmoides.

On examining the inner surface of this bone at its under and middle part, we observe an elevation in form of a ridge, which has been called the spinous process; it ascends for some way, dividing the bone into two considerable fossae, in which the anterior lobes of the brain are placed. To a narrow furrow in this ridge is attached the extremity of the falx, as the membrane is called, which divides the brain into two hemispheres. The furrow becoming gradually wider, is continued to the upper and back part of the bone. It has the falx fixed to it, and part of the longitudinal sinus lodged in it. Besides the two fossae, there are many depressions, which appear like digital impressions, and owe their formation to the prominent circumvolutions of the brain.

In the fetus, the forehead is composed of two distinct bones; so that in them the sagittal suture reaches from the os occipitis to the nose. This bone is almost everywhere composed of two tables and a diploe. These two tables separating from each other under the eyes, form two cavities, one on each side of the face, called the frontal sinuses. These sinuses are lined with a soft membrane, called membrana pituitaria. In these sinuses a mucus is secreted, which is constantly passing through two small holes into the nostrils, which it serves to moisten.

The os frontis is joined by sutures to many of the bones of the head, viz. to the parietal, maxillary, and temporal bones; to the os ethmoides; os sphenoides; os uncus; and ossa naso. The suture which connects it with the parietal bones is called the coronal suture.

The parietal bones are two in number; they are very thin, and even transparent in some places. The particular figure of each of these bones is that of an irregular square, bordered with indentations through its whole circumference, except at its lower part. It will be easily conceived, that these bones which compose the superior and lateral parts of the cranium, and cover the greatest part of the brain, form a kind of vault. On their inner surface we observe the marks of the vessels of the dura mater; and at their upper edge the groove for the superior longitudinal sinus.

The ossa parietalia are joined to each other by the sagittal suture; to the os sphenoides and ossa temporum by the squamosus suture; to the os occipitis by the lambdoidal suture (G), so called from its resemblance to the Greek letter lambda; and to the os frontis by the coronal suture.

In the fetus, the parietal bones are separated from the middle of the divided os frontis by a portion of the cranium then unossified.

The occipital bone forms the posterior and inferior parts of the skull; it approaches nearly to the shape of a lozenge, and is indented throughout three parts of its circumference.

There is a considerable hole in the inferior portion of this bone, called the foramen magnum, through which Osteology, the medulla oblongata passes into the spine.—The nervi accessorii, and vertebral arteries, likewise pass through it. Behind the condyles are two holes for the passage of cervical veins into the lateral sinuses; and above them are two others for the passage of the eighth pair and accessory nerves out of the head. At the sides, and a little on the anterior part of the foramen magnum, are two processes, called the condyles, one on each side; they are of an oval figure, and are covered with cartilage.

The external surface of this bone has a large transverse arched ridge, under which the bone is very irregular, where it affords attachment to several muscles. On examining its inner surface, we may observe two ridges in form of a cross; one ascending from near the foramen magnum to the top of the bone; the upper end of this, in which the falx is fixed, is hollow, for lodging the superior longitudinal sinus; and the under end has the third process of the dura mater fixed to it. The other ridge, which runs horizontally, is likewise hollow for containing the lateral sinuses. Four fossae are formed by the cross, two above and two below. In the former are placed the posterior lobes of the brain, and in the latter the lobes of the cerebellum.

At the basis of the cranium, we observe the cuneiform process, (which is the name given to the great apophysis at the fore part of this bone); it serves for the reception of the medulla oblongata.

The os occipitis is of greater strength and thickness than either of the other bones of the head, though irregularly so; at its inferior part, where it is thinnest, it is covered by a great number of muscles.

This bone, from its situation, being more liable to be injured by falls than any other bone of the head, nature has wisely given it the greatest strength at its upper part, where it is most exposed to danger.

It is joined to the parietal bones by the lambdoidal suture, and to the ossa temporum by the additamentum of the temporal suture. It is likewise connected to the os sphenoides by the cuneiform process. It is by means of the os occipitis that the head is united to the trunk, the two condyles of this bone being connected to the superior oblique processes of the first vertebra of the neck.

There are two temporal bones, one on each side.—Of the teeth We may distinguish in them two parts; one of which is called the squamosus or scaly part, and other pars petrosa from its hardness. This last is shaped like a pyramid.

Each of these divisions affords processes and cavities; externally there are three processes; one anterior, called the zygomatic process; one posterior, called the mastoid mamillary process, from its resemblance to a nipple; and one inferior, called the styloid process, because it is shaped like a stiletto, or dagger.

The cavities are, 1. The meatus auditorius externus. 2. A large fossa which serves for the articulation of the lower jaw; it is before the meatus auditorius, and immediately under the zygomatic process. 3. The style-mastoid.

(G) The lambdoidal suture is sometimes very irregular, being composed of many small sutures, which surround so many little bones called ossa triquetra, though perhaps improperly, as they are not always triangular. Osteology. stylo-mastoid hole, so called from its situation between the styloid and mastoid processes; it is likewise styled the aqueduct of Fallopia, and affords a passage to the portio dura of the auditory or seventh pair of nerves.

4. Below, and on the fore part of the last foramen, we observe part of the jugular fossa, in which the beginning of the internal jugular vein is lodged. Anterior and superior to this fossa is the orifice of a foramen, through which passes the carotid artery. This foramen runs first upwards and then forwards, forming a kind of elbow, and terminates at the end of the os petrosum.

At this part of each temporal bone, we may observe the opening of the Eustachian tube, a canal which passes from the ear to the back part of the nose.

In examining the internal surface of these bones, we may remark the triangular figure of their petrous part which separates two fossae; one superior and anterior; the other inferior and posterior: the latter of these composes part of the fossa, in which the cerebellum is placed; and the former, a portion of the least fossa for the basis of the brain. On the posterior side of the pars petrosa, we observe the meatus auditorius internus, into which enters the double nerve of the seventh pair. On the under side of this process, part of a hole appears, which is common to the temporal and occipital bones; through it the lateral sinus, the eighth pair, and accessory nerves pass out of the head.

The pars petrosa contains several little bones called the bones of the ear; which, as they do not enter into the formation of the cranium, shall be described when we are treating of the organs of hearing.

The ossa temporum are joined to the ossa maxillaria, by the zygomatic sutures; to the parietal bones by the squamosus sutures; to the os occipitis, by the lambdoidal suture; and to the sphenoid bone, by the suture of that name.

This bone, from its situation amidst the other bones of the head, has been sometimes called cuneiforme. It is of a very irregular figure, and has been compared to a hat with its wings extended.

It is commonly divided into its middle part or body, and its sides or wings.

The fore part of the body has a spine or ridge, which makes part of the septum narium. The upper part of each wing forms a share of the temple. The fore part of this belongs to the orbit; while the under and back part, termed spinous process, is lodged in the base of the skull at the point of the pars petrosa. But two of the most remarkable processes are the pterygoid or aliform, one on each side of the body of the bone, and at no great distance from it. Each of these processes is divided into two wings, and of these the exterior one is the widest. The other terminates in a hook-like process.

The internal surface of this bone affords three fossae. Two of these are formed by the wings of the bone, and make part of the lesser fossae of the basis of the cranium. The third, which is smaller, is on the top of the body of the bone; and is called sella turcica, from its resemblance to a Turkish saddle. This fossa, in which the pituitary gland is placed, was posteriorly and anteriorly processes called the clinoid processes.

There are twelve holes in this bone, viz. six on each side. The first is the passage of the optic nerve and ocular artery; the second, or large slit, transmits the third, fourth, sixth, and first part of the fifth pair of nerves with the ocular vein; the third hole gives passage to the second branch of the fifth pair; and the fourth hole to the third branch of the fifth pair of nerves. The fifth hole is the passage of the artery of the dura mater. The sixth hole is situated above the pterygoid process of the sphenoid bone: through it a reflected branch of the second part of the fifth pair passes.

Within the substance of the os sphenoides there are two sinuses separated by a bony plate. They are lined with the pituitary membrane; and, like the frontal sinuses, separate a mucus which passes into the nostrils.

The os sphenoides is joined to all the bones of the cranium; and likewise to the ossa maxillaria, ossa malarum, ossa palati, and vomer.

This bone makes part of the basis of the skull, assists in forming the orbits, and affords attachment to several muscles.

The os ethmoides is situated at the fore part of the basis of the cranium, and is of a very irregular figure. From the great number of holes with which it is pierced, it is sometimes called os cribriforme, or sieve-like bone.

It consists of a middle part and two sides. The middle part is formed of a thin bony plate, in which ethmoid filaments of the olfactory nerve. From the middle of this plate, both on the outside, and from within, there rises up a process, which may be easily distinguished. The inner one is called crista galli, from its supposed resemblance to a cock's comb. To this process the falx of the dura mater is attached. The exterior process, which has the same common basis as the crista galli, is a fine lamella which is united to the vomer; and divides the cavity of the nostrils, though unequally, it being generally a little inclined to one side.

The lateral parts of this bone are composed of a cellular substance; and these cells are so very intricate, that their figure or number cannot be described. Many writers have on this account called this part of the bone the labyrinth. These cells are externally covered with a very thin bony lamella. This part of the bone is called the os planum, and forms part of the orbit.

The different cells of this bone, which are numerous, and which are everywhere lined with the pituitary membrane, evidently serve to enlarge the cavity of the nose, in which the organ of smelling resides.

This bone is joined to the os sphenoides, os frontis, ossa maxillaria, ossa palati, ossa naso, ossa unguis, and vomer.

The ancients, who considered the brain as the seat of all the humours, imagined that this viscus discharged its redundant moisture through the holes of the ethmoid bone. And the vulgar still think, that abscesses of the brain discharge themselves through the mouth and ears, and that snuff is liable to get into the head; but neither snuff nor the matter of an abscess are more capable of passing through the cribriform bone, than the serosity which they supposed was discharged through it in a common cold. All the holes of the ethmoid bone are filled up with the branches of the olfactory nerve. Its inner part is likewise covered with the dura mater, and its cells are everywhere lined with The face, which consists of a great number of bones, is commonly divided into the upper and lower jaws. Of the teeth. Of these, six are placed on each side of the maxilla superior, and one in the middle.

The bones, which are in pairs, are the ossa malarum, ossa maxillaria, ossa nasi, ossa unguis, ossa palati, and ossa spongiosa inferiora. The single bone is the vomer.

These are the prominent square bones which are placed under the eyes, forming parts of the orbits and maxillae, the upper part of the cheeks. Each of them affords three surfaces: one exterior and a little convex; a second superior and concave, forming the inferior part and sides of the orbit; and a third posterior, irregular, and hollowed for the lodgment of the lower part of the temporal muscle.

The angles of each bone form four processes, two of which may be called orbital processes: of these the upper one is joined by suture to the os frontis, and that below to the maxillary bone. The third is connected with the os sphenoides by means of the transverse suture; and the fourth is joined to the zygomatic process of the temporal bone, with which it forms the zygoma.

These bones, which are of a very irregular figure, are so called because they form the most considerable portion of the upper jaw. They are two in number, superior and generally remain distinct through life.

Of the many processes which are to be seen on these bones, and which are connected with the bones of the face and skull, we shall describe only the most remarkable.

One of these processes is at the upper and fore part of the bone, making part of the side of the nose, and called the nasal process. Another forms a kind of circular sweep at the inferior part of the bone, in which are the alveoli or sockets for the teeth: this is called the alveolar process. A third process is united to the os maxale on each side. Between this and the nasal process there is a thin plate, which forms a share of the orbit, and lies over a passage for the superior maxillary vessels and nerves.—The alveolar process has posteriorly a considerable tuberosity on its internal surface, called the maxillary tuberosity.

Behind the alveolar process we observe two horizontal lamellae, which uniting together, form part of the roof of the mouth, and divide it from the nose. The hollowness of the roof of the mouth is owing to this partition's being seated somewhat higher than the alveolar process.—At the fore part of the horizontal lamellae there is a hole called foramen incisivum, through which small blood vessels and nerves go between the mouth and nose.

In viewing these bones internally, we observe a fossa in the inferior portion of the nasal process, which, with the os unguis and os spongiosum inferius, forms a passage for the lachrymal duct.

Where these two bones are united to each other, they project somewhat upwards and forwards, leaving between them a furrow, into which the lower portion of the septum nasi is admitted.

Each of these bones being hollow, a considerable si- The ossa maxillaria are connected with the greater part of the bones of the face and cranium, and assist in forming not only the cheeks, but likewise the palate, nose, and orbits.

The ossa naso form two irregular squares. They are thicker and narrower above than below. Externally they are somewhat convex, and internally slightly concave. These bones constitute the upper part of the nose. At their fore part they are united to each other, above to the os frontis, by their sides to the ossa maxillaria superiora, posteriorly and inferiorly to the septum narium, and below to the cartilages that compose the rest of the nostrils.

These little transparent bones owe their name to their supposed resemblance to a finger nail. Sometimes they are called ossa lachrymalia, from their concurring with the nasal process of each maxillary bone in forming a lodgment for the lachrymal sac and duct.

The ossa unguis are of an irregular figure. Their external surface consists of two smooth parts, divided by a middle ridge. One of these parts, which is concave and nearest to the nose, serves to support the lachrymal sac and part of the lachrymal duct. The other, which is flat, forms a small part of the orbit.

Each of these bones is connected with the os frontis, os ethmoides, and os maxillare superius.

These bones, which are situated at the back part of the roof of the mouth, between the os sphenoides and the ossa maxillaria superiora, are of a very irregular shape, and serve to form the nasal and maxillary fossa, and a small portion of the orbit. Where they are united to each other, they rise up into a spine on their internal surface. This spine appears to be a continuation of that of the superior maxillary bones, and helps to form the septum narium.

These bones are joined to the ossa maxillaria superiora, os ethmoides, os sphenoides, and vomer.

This bone derives its name from its resemblance to a ploughshare. It is a long and flat bone, somewhat thicker at its back than at its fore part. At its upper part we observe a furrow extending through its whole length. The posterior and largest part of this furrow receives a process of the sphenoid bone. From this the furrow advances forwards, and becoming narrower and shallower, receives some part of the nasal lamella ethmoides; the rest serves to support the middle cartilage of the nose.

The inferior portion of this bone is placed on the nasal spine of the maxillary and palate bones, which we mentioned in our description of the ossa palati.

The vomer is united to the os sphenoides, os ethmoides, ossa maxillaria superiora, and ossa palati. It forms part of the septum narium, by dividing the back part of the nose into two nostrils.

The parts which are usually described by this name, do not seem to deserve to be distinguished as distinct bones, except in young subjects. They consist of a spongy lamella in each nostril, which is united to the spongy lamina of the ethmoid bone, of which they are considered as a part.

Each of these lamellae is longest from behind forwards; with its convex surface turned towards the septum narium, and its concave part towards the maxillary bone, covering the opening of the lachrymal duct into the nose.

These bones are covered with the pituitary membrane; and besides their connexion with the ethmoid bone, are joined to the ossa maxillaria superiora, ossa palati, and ossa unguis.

The maxilla inferior, or lower jaw, which in its shape resembles a horse shoe, consists of two distinct bones in the fetus; but these unite together soon after birth, or so as to form only one bone. The upper edge of this bone, like the os maxillare superius, has an alveolar process, furnished with sockets for the teeth.

On each side the posterior part of the bone rises almost perpendicularly into two processes. The highest of these, called the coronoid process, is pointed and thin, and serves for the insertion of the temporal muscle. The other, or condyloid process, as it is called, is shorter and thicker, and ends in an oblong rounded head, which is received into a fossa of the temporal bone, and is formed for a moveable articulation with the cranium. This joint is furnished with a moveable cartilage. At the bottom of each coronoid process, on its inner part, we observe a foramen extending under the roots of all the teeth, and terminating at the outer surface of the bone near the chin. Each of these canals transmits an artery, vein, and nerve, from which branches are sent off to the teeth.

The lower jaw is capable of a great variety of motion. By sliding the condyles from the cavity towards the eminences on each side, we bring it horizontally forwards, as in biting; or we may bring the condyles only forward, and tilt the rest of the jaw backwards, as in opening the mouth. We are likewise able to slide the condyles alternately backwards and forwards from the cavity to the eminence, and vice versa, as in grinding the teeth. The cartilages, by adapting themselves to the different inequalities in these several motions of the jaw, serve to secure the articulation, and to prevent any injuries from friction.

The alveolar processes are composed of an outer and inner bony plate, united together by thin partitions, which at the fore part of the jaw divide the processes into as many sockets as there are teeth. But at the back part of the jaw, where the teeth have more than one root, we find a distinct cell for each root. In both jaws these processes begin to be formed with the teeth; they likewise accompany them in their growth, and gradually disappear when the teeth are removed.

§ 3. Of the Teeth.

The teeth are bones of a particular structure, formed for the purposes of mastication and the articulation of the voice. It will be necessary to consider their composition and figure, their number and arrangement, and the time and order in which they appear.

In each tooth we may distinguish a body, a neck, and a root or fangs.

The body of the tooth is that part which appears above The teeth are composed of two substances, viz., enamel and bone. The enamel, or the vitreous or cortical part of the tooth, is a white and very hard and compact substance peculiar to the teeth, and appears fibrous or striated when broken. This substance is thickest on the grinding surface, and becoming gradually thinner, terminates insensibly at the neck of the tooth. Ruyssch * affirmed, that he could trace the arteries into the hardest part of the teeth; Leeuwenhoek † suspected the fibres of the enamel to be so many vessels; and Monro ‡ says, he has frequently injected the vessels of the teeth in children, so as to make the inside of the cortex appear perfectly red. But it is certain, that it is not tinged by a madder diet, and that no injection will ever reach it, so that it has no appearance of being vascular.

The bony part, which composes the inner substance of the body, neck, and root of the tooth, resembles other bones in its structure, but it is much harder than the most compact part of bones in general. As a tooth when once formed receives no tinge from a madder diet, and as the minutest injections do not penetrate into its substance, this part of a tooth has, like the enamel, been supposed not to be vascular. But when we consider that the fangs of a tooth are invested by a periosteum, and that the swellings of these fangs are analogous to the swellings of other bones, we may reasonably conclude, that there is a similarity of structure; and that this bony part has a circulation through its substance; although from its hardness we are unable to demonstrate its vessels.

In each tooth we find an inner cavity, into which enter an artery, vein, and nerve. This cavity begins by a small opening, and becoming larger, terminates in the body of the tooth. In advanced life this hole sometimes closes, and the tooth is of course rendered insensible.

The periosteum surrounds the teeth from their fangs to a little beyond their bony sockets, where we find it adhering to the gums. This membrane, while it encloses the teeth, serves at the same time to line the sockets; so that it may be considered as common to both.

The teeth are likewise secured in their sockets by means of the gums; a red, vascular, firm, and elastic substance, that possesses but little sensibility. In the gums of infants we find a hard ridge extending through their whole length, but no such ridge is to be seen in old people who have lost their teeth.

The number of the teeth in both jaws at full maturity, usually varies from twenty-eight to thirty-two. They are commonly divided into three classes, viz., incisors, canini, and grinders or molares (H). The incisors are the four teeth in the fore part of each jaw. They have each of them two surfaces; one anterior and convex, the other posterior and slightly concave, both of which terminate in a sharp edge. They are called incisors from their use in dividing the food. They are usually broader and thicker in the upper than in the under jaw; and, by being placed somewhat obliquely, generally fall over the latter.

The canini derive their name from the resemblance to a dog's tusks, being the longest of all the teeth. We find one on each side of the incisors, so that there are two canini in each jaw. Their fang resembles that of the incisors, but is much larger; and in their shape they appear like an incisor with its edge worn off, so as to terminate in a narrow point.

These teeth not being calculated for cutting and dividing the food like the incisors, or for grinding it like the molares, seem to be intended for laying hold of substances (T).

The molares or grinders, of which there are ten in each jaw, are so called, because from their shape and size they are fitted for grinding the food. Each of the incisors and canini is furnished only with one fang; but in the molares of the under jaw we constantly find two fangs, and in those of the upper jaw three fangs. These fangs are sometimes separated into two points, and each of these points has sometimes been described as a distinct fang.

The two first of the molares, or those nearest to the canine teeth on each side, differ from the other three, and are with great propriety named bicuspides by Mr Hunter. They have sometimes only one root, and seem to be of a middle nature between the incisors and the larger molares. The two next are much larger. The fifth or last grinder on each side is smaller and shorter than the rest; and from its not cutting the gum till after the age of twenty, and sometimes not till much later in life, it is called dens sapientia.

There is in the structure and arrangement of all these teeth an art which cannot be sufficiently admired. To understand it properly, it will be necessary to consider the under jaw as a kind of lever, with its fixed points at its articulations with the temporal bones: it will be right to observe, too, that its powers arise from its different muscles, but in elevations chiefly from the temporalis and masseter; and that the aliment constitutes the object of resistance. It will appear, then, that the molares, by being placed nearest the centre of motion, are calculated to press with a much greater force than the other teeth, independent of the grinding powers which they possess by means of the pterygoid muscles; and that it is for this reason we put between them any hard body we wish to break.

The canini and incisors are placed farther from this point, and of course cannot exert so much force; but

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(H) Mr Hunter has thought proper to vary this division. He retains the old name of incisores to the four fore teeth, but he distinguishes the canine teeth by the name of the cuspidati. The two teeth which are next to these, and which have been usually ranked with the molares, he calls the bicuspides; and he gives the name of grinders only to the three last teeth on each side.

(1) Mr Hunter remarks of these teeth, that we may trace in them a similarity in shape, situation, and use, from the most imperfectly carnivorous animal, which we believe to be the human species, to the lion, which is the most perfectly carnivorous. Osteology, they are made for cutting and tearing the food, and this form seems to make amends for their deficiency in strength.

There are examples of children who have come into the world with two, three, and even four teeth; but these examples are very rare; and it is seldom before the seventh, eighth, or ninth month after birth, that the incisors, which are the first formed, begin to pass through the gum. The symptoms of dentition, however, in consequence of irritation from the teeth, frequently take place in the fourth or fifth month. About the twentieth or twenty-fourth month, the canini and two molares make their appearance.

The dangerous symptoms that sometimes accompany dentition, are owing to the pressure of the teeth on the gum, which they irritate so as to excite pain and inflammation. This irritation seems to occasion a gradual wasting of the gum at the part, till at length the tooth makes its appearance.

The symptoms are more or less alarming, in proportion to the resistance which the gum affords to the teeth, and according to the number of teeth which may chance to seek a passage at the same time. Were they all to appear at once, children would fall victims to the pain and excessive irritation; but nature has so very wisely disposed them, that they usually appear one after the other, with some distance of time between each. The first incisor that appears is generally in the lower jaw, and is followed by one in the upper jaw. Sometimes the canini, but more commonly one of the molares, begins to pass through the gum first.

These 20 teeth, viz. eight incisores, four canini, and eight molares, are called temporary or milk teeth, because they are all shed between the age of seven and 14, and are succeeded by what are called the permanent or adult teeth. The latter are of a firmer texture, and have larger fangs.

These adult teeth being placed in a distinct set of alveoli, the upper sockets gradually disappear, as the under ones increase in size, till at length the temporary or upper teeth, having no longer any support, consequently fall out.

To these 20 teeth which succeed the temporary ones, 12 others are afterwards added, viz. three molares on each side in both jaws: and in order to make room for this addition, we find that the jaws gradually lengthen in proportion to the growth of the teeth; so that with 32 teeth, they seem to be as completely filled as they are afterwards with 32. This is the reason why the face is rounder and flatter in children than in adults.

With regard to the formation of the teeth, we may observe, that in a fetus of four months, the alveolar process appears only as a shallow longitudinal groove, divided by minute ridges into a number of intermediate depressions; in each of which we find a small pulpy substance, surrounded by a vascular membrane. This pulp gradually ossifies, and its lower part is lengthened out to form the fang. When the bony part of the tooth is formed, its surface begins to be incrusted with the enamel. How the latter is formed and deposited, we are not yet able to determine.

The rudiments of some of the adult teeth begin to be formed at a very early period, for the pulp of one of the incisors may generally be perceived in a fetus of eight months, and the ossification begins in it soon after birth. The first bicuspid begins to ossify about the fifth or sixth, and the second about the seventh year. The first adult grinder cuts the gum about the 12th, the second about the 18th, and the third, or dens sapientiae, usually between the 20th and 30th year.

The teeth, like other bones, are liable to be affected by disease. Their removal is likewise the natural consequence of old age; for as we advance in life, the alveoli fill up, and the teeth, especially the incisors, fall out. When this happens, the chin projects forward, and the face is much shortened.

§ 4. Of the Os Hyoides (κ).

The os hyoides, which is placed at the root of the tongue, was so called by the ancients on account of its supposed resemblance to the Greek letter υ.

It will be necessary to distinguish in it, its body, horns, and appendices.

The body, which is the middle and broadest part of the bone, is so placed that it may be easily felt at the fore part of the throat. Anteriorly it is irregularly convex, and its inner surface is unequally concave. Its cornua, or horns, which are flat and a little bent, being much longer than the body part, may be described as forming the sides of the υ. The appendices, or little horns, as they are called by M. Winslow and some other writers, are two processes which rise up from the articulations of the cornua with the body, and are usually connected with the styloid process on each side by means of a ligament.

The uses of this bone are to support the tongue and afford attachment to a great number of muscles; some of which perform the motions of the tongue, while others act on the larynx and fauces.

Sect. III. Of the Bones of the Trunk.

The trunk of the skeleton consists of the spine, the thorax, and the pelvis.

§ 1. Of the Spine.

The spine is composed of a great number of bones called vertebrae, forming a long bony column, in figure not much unlike the letter S. This column, which extends from the head to the lower part of the body, may be said to consist of two irregular and unequal pyramids, united to each other in that part of the loins where the last lumbar vertebra joins the os sacrum.

The vertebrae of the upper and longest pyramid are called

(k) This bone is very seldom preserved with the skeleton, and cannot be included amongst the bones of the head or in any other division of the skeleton. Thomas Bartholin has perhaps very properly described it among the parts contained in the mouth; but the generality of anatomical writers have placed it, as it is here, after the bones of the face. In advanced life these cartilages become shrivelled, Osteology, and of course lose much of their elasticity. This may serve to account for the decrease in stature and the stooping forward which are usually to be observed in old people.

Besides the connexion of the several vertebrae by means of this intervertebral substance, there are likewise many strong ligaments, both external and internal, which unite the bones of the spine to each other. Their union is also strengthened by a variety of strong muscles that cover and surround the spine.

The bones of the spine are found to diminish in density, and to be less firm in the texture, in proportion as they increase in bulk; so that the lowermost vertebrae, though the largest, are not so heavy in proportion as the upper ones. By this means the size of these bones is increased without adding to their weight; a circumstance of no little importance in a part like the spine, which, besides flexibility and suppleness, seems to require lightness as one of its essential properties.

In very young children, each vertebra consists of three bony pieces united by cartilages which afterwards ossify.

There are seven vertebrae of the neck—they are of a firmer texture than the other bones of the spine. Their transverse processes are forked for the lodgment of muscles, and at the bottom of each we observe a foramen, through which pass the cervical artery and vein. The first and second of these vertebrae must be described more particularly. The first approaches almost to an oval shape.—On its superior surface it has two cavities which admit the condyles of the occipital bone with which it is articulated. This vertebra, which is called atlas from its supporting the head, cannot well be described as having either body or spinous process, being a kind of bony ring. Anteriorly, where it is articulated to the odontoid process of the second vertebra, it is very thin. On its upper surface it has two cavities which admit the condyles of the occipital bone. By this connexion the head is allowed to move forwards and backwards, but has very little motion in any other direction.

The second vertebra has gotten the name of dentata, from its having, at its upper and anterior part, a process called the odontoid or tooth-like process, which is articulated with the atlas, to which this second vertebra may be said to serve as an axis. This odontoid process is of a cylindrical shape, somewhat flattened, however, anteriorly and posteriorly. At its fore part where it is received by the atlas, we may observe a smooth, convex, articulating surface. It is by means of this articulation that the head performs its rotatory motion, the atlas in that case moving upon this odontoid process as upon a pivot. But when this motion is in any considerable degree, or, in other words, when the head moves much either to the right or left, all the cervical vertebrae seem to assist, otherwise the spinal marrow would be in danger of being divided transversely by the first vertebra.

The spinous process of each of the cervical vertebrae is shorter, and their articular processes more oblique, than in the other bones of the spine.

These 12 vertebrae are of a middle size between those of the neck and loins. At their sides we may observe two depressions, one at the upper and the other at the lower Osteology. lower part of the body of each vertebra; which uniting with similar depressions in the vertebrae above and below, form articulating surfaces, covered with cartilages, for receiving the heads of the ribs; and at the fore part of their transverse process (excepting the two last) we find an articulating surface for receiving the tuberosity of the ribs.

These five vertebrae differ only from those of the back in their being larger, and in having their spinous processes at a greater distance from each other. The most considerable motions of the trunk are made on these vertebrae; and these motions could not be performed with so much ease, were the processes placed nearer to each other.

Os sacrum. The os sacrum, which is composed of five or six pieces in young subjects, becomes one bone in more advanced age.

It is nearly of a triangular figure, its inferior portion being bent a little forwards. Its superior part has two oblique processes, which are articulated with the last of the lumbar vertebrae; and it has likewise commonly three small spinous processes, which gradually become shorter, so that the lowermost is not so long as the second, nor the second as the uppermost. Its transverse processes are formed into one oblong process, which becomes gradually smaller as it descends. Its concave or anterior side is usually smooth, but its posterior convex side has many prominences (the most remarkable of which are the spinous processes just now mentioned), which are filled up and covered with the muscular and tendinous parts behind.

This bone has five pair of holes, which afford a passage to blood vessels, and likewise to the nerves that are derived from the spinal marrow, which is continued even here, being lodged in a triangular cavity, that becomes smaller as it descends, and at length terminates obliquely at the lower part of this bone. Below the third division of the os sacrum, this canal is not completely bony as the rest of the spine, being secured at its back part only by a very strong membrane, so that a wound at this part must be extremely dangerous.

The os sacrum is united laterally to the ossa innominata, or hip-bones, and below to the coccyx. The coccyx, which, like the os sacrum, is in young people made up of three or four distinct parts, usually becomes one bone in the adult state.

It serves to support the intestinum rectum; and, by its being capable of some degree of motion at its articulation with the sacrum, and being like that bone bent forwards, we are enabled to sit with ease.

This bone is nearly of a triangular shape, being broadest at its upper part, and from thence growing narrower to its apex, where it is not bigger than the little finger.

It has got its name from its supposed resemblance to a cuckow's beak. It differs greatly from the vertebrae, being commonly without any processes, and having no cavity for the spinal marrow, or foramina for the transmission of nerves.

The spine, of which we have now finished the anatomical description, is destined for many great and important uses. The medulla spinalis is lodged in its bony canal secure from external injury. It serves as a defence to the abdominal and thoracic viscera, and at the same time supports the head, and gives a general firmness to the whole trunk.

We have before compared it to the letter f, and its different turns will be found to render it not very unlike the figure of that letter.—In the neck we see it projecting somewhat forward to support the head, which, without this assistance, would require a greater number of muscles. Lower down, in the thorax, we find it taking a curved direction backwards, and of course increasing the cavity of the chest. After this, in the loins, it again projects forwards in a direction with the centre of gravity, by which means we are easily enabled to keep the body in an erect posture, for otherwise we should be liable to fall forwards. Towards its inferior extremity, however, it again recedes backward, and thus assists in forming the pelvis, the name given to the cavity in which the urinary bladder, intestinum rectum, and other viscera are placed.

If this bony column had been formed only of one piece, it would have been much more easily fractured than it is now; and by confining the trunk to a stiff situation, a variety of motions would have been altogether prevented, which are now performed with ease by the great number of bones of which it is composed.

It is firm, and yet to this firmness there is added a perfect flexibility. If it be required to carry a lead upon the head, the neck becomes stiff with the assistance of its muscles, and accommodates itself to the load, as if it was composed only of one bone.—In stooping likewise, or in turning to either side, the spine turns itself in every direction, as if all its bones were separated from each other.

In a part of the body like the spine, that is made up of so great a number of bones, and intended for such a variety of motion, there must be a greater danger of dislocation than fracture; but we shall find, that this is very wisely guarded against in every direction by the processes belonging to each vertebra, and by the ligaments, cartilages, &c. by which these bones are connected with each other.

§ 2. Of the Bones of the Thorax.

The thorax, or chest, is composed of many bones, viz. the sternum which is placed at its anterior part, twelve ribs on each side which make up its lateral parts, and the dorsal vertebrae which constitute its posterior part. These last have been already described.

The sternum is the long bone which extends itself from the upper to the lower part of the breast anterio-rily, and to which the ribs and the clavicles are articulated.

In children it is composed of several bones united by cartilages; but as we advance in life, most of these cartilages ossify, and the sternum in the adult state is found to consist only of three pieces, and sometimes becomes one bone. It is however generally described as being composed of three parts—one superior, which is broad, thick, and short; and one in the middle, which is thinner, narrower, and longer than the other.

It terminates at its lower part by a third piece, which is called the xiphoid, or sword-like cartilage, from its supposed resemblance to the blade of a sword, and because in young subjects it is commonly in a cartilaginous state. We have already observed, that this bone is articulated with the clavicle on each side. It is likewise joined to the fourteen true ribs, viz. seven on its right and seven on its left side.

The ribs are bones shaped like a bow, forming the sides of the chest. There are twelve on each side. They are distinguished into true and false ribs: The seven upper ribs which are articulated to the sternum are called true ribs, and the five lower ones that are not immediately attached to that bone are called false ribs.

On the inferior and interior surface of each rib, we observe a sinuosity for the lodgment of an artery, vein, and nerve.

The ribs are not bony through their whole length, their anterior part being cartilaginous. They are articulated with the vertebrae and sternum. Every rib (or at least the greater number of them) has at its posterior part two processes; one at its extremity, called the head of the rib, by means of which it is articulated with the body of two vertebrae; and another, called its tuberosity, by which it is articulated with the transverse process of the lowest of these two vertebrae. The first rib is not articulated by its extremity to two vertebrae, being simply attached to the upper part of the first vertebra of the back. The seven superior or true ribs are articulated anteriorly with the sternum by their cartilages; but the false ribs are supported in a different manner—the eighth, which is the first of these ribs, being attached by its cartilages to the seventh; the ninth to the eighth, &c.

The two lowermost ribs differ likewise from all the rest in the following particulars: They are articulated only with the body of a vertebra, and not with a transverse process; and anteriorly, their cartilage is loose, not being attached to the cartilages of the other ribs; and this seems to be, because the most considerable motions of the trunk are not performed on the lumbar vertebrae alone, but likewise on the two last vertebrae of the back: so that if these two ribs had been confined at the fore part like the other ribs, and had been likewise articulated with the bodies of two vertebrae, and with the transverse processes, the motion of the two last vertebrae, and consequently of the whole trunk, would have been impeded.

The ribs help to form the cavity of the thorax; they afford attachment to different muscles; they are useful in respiration; and they serve as a security to the heart and lungs.

§ 3. Of the Bones of the Pelvis.

The pelvis is composed of the os sacrum, os coccygis, and two ossa innominata. The two first of these bones were included in the account of the spine, to which they more properly belong.

In children, each os innominatum is composed of three distinct bones; but as we advance in life the intermediate cartilages gradually ossify, and the marks of the original separation disappear, so that they become one irregular bone; still, however, continuing to retain the names of ilium, ischium, and pubis, by which their divisions were originally distinguished, and to be described as three different bones by the generality of anatomists. The os ilium forms the upper and most considerable part of the bone, the os ischium its lower and posterior portion, and the os pubis its fore part.

The os ilium, or haunch-bone, is articulated posteriorly to the os sacrum by a firm cartilaginous substance, and is united to the os pubis before and to the os ischium below. Its superior portion is thin, and terminates in a ridge called the crista or spine of the ilium, and more commonly known by the name of the haunch. This crista rises up like an arch, being turned somewhat outwards, so as to resemble the wings of a phaeton.

Externally this bone is unequally prominent and hollowed for the lodgment of muscles; internally we find it smooth and concave. At its lower part there is a considerable ridge on its inner surface. This ridge extends from the os sacrum, and corresponds with a similar prominence both on that bone and the ischium; forms with the inner part of the ossa pubis what in midwifery is termed the brim of the pelvis.

The crista, or spine, which at first is an epiphysis, has two considerable tuberosities; one anteriorly, and the other posteriorly, which is the largest of the two: These, from their projecting more than the parts of the bone below them, have gotten the name of spinal processes. From the anterior spinous process, the sartorius and tensor vaginae femoris muscles have their origin; and below the posterior process we observe a considerable niche in the bone, which, in the recent subject, is formed into a large foramen, by means of a strong ligament that is stretched over its lower part from the os sacrum to the sharp-pointed process of the ischium. This hole affords a passage to the great sciatic nerve, and to the posterior crural vessels under the pyriform muscle, part of which likewise passes out here.

The os ischium, or hip-bone, which is of a very irregular figure, constitutes the lower lateral parts of the pelvis, and is commonly divided into its body, tuberosity, and ramus. The body forms the lower and most considerable portion of the acetabulum, and sends a sharp-pointed process backwards, called the spine of the ischium. To this process the ligament adheres, which was just now spoken of, as forming a foramen for the passage of the sciatic nerve. The tuberosity, which is the lowest part of the trunk, and supports us when we sit, is large and irregular, affording origin to several muscles. From this tuberosity we find the bone becoming thinner and narrower. This part, which has the name of ramus or branch, passes forwards and upwards, and concurs with the ramus of the os pubis, to form a large hole called the foramen magnum ischi, or thyroidicum, as it is sometimes named from its resemblance to a door or shield. This hole, which in the recent subject is closed by a strong membrane called the obturator ligament, affords through its whole circumference attachment to muscles. At its upper part where we observe a niche in the bone, it gives passage to the obturator vessels and nerves, which go to the inner part of the thigh. Nature seems everywhere to avoid an unnecessary weight of bone, and this foramen, no doubt, serves to lighten the bones of the pelvis.

The os pubis or share-bone, which with its fellow forms the fore part of the pelvis, is the smallest division of the os innominatum. It is united to its fellow by... by means of a strong cartilage, which forms what is called the symphysis pubis.

In each os pubis we may distinguish the body of the bone, its angle and ramus. The body or outer part is united to the os ilium. The angle comes forwards to form the symphysis, and the ramus is a thin process which unites with the ramus of the ischium, to form the foramen thyroideum.

The three bones we have described as composing each os innominatum, all assist in forming the acetabulum, in which the head of the os femoris is received.

This cavity is everywhere lined with a smooth cartilage, excepting at its inner part, where we may observe a little fossa, in which are lodged the mucilaginous glands of the joint. We may likewise notice the pit or depression made by the round ligament, as it is improperly called, which, by adhering to this cavity and to the head of the thigh-bone, helps to secure the latter in the socket.

These bones, which are united to each other and to the spine, by many very strong ligaments, serve to support the trunk, and to connect it with the lower extremities; and at the same time to form the pelvis or basin, in which are lodged the intestines and urinary bladder, and in women the uterus; so that the study of this part of osteology is of the utmost importance in midwifery.

It is worthy of observation, that in women the os sacrum is usually shorter, broader, and more hollowed, the osa ilia more expanded, and the inferior opening of the pelvis larger, than in men.

Sect. IV. Of the Extremities.

The parts of the skeleton consist of the upper extremity and the lower.

§ I. Of the Upper Extremities.

This consists of the shoulder, the arm, and the hand.

1. Of the Shoulder.

The shoulder consists of two bones, the clavicle and the scapula.

The former, which is so named from its resemblance to the key in use among the ancients, is a little curved at both its extremities like an Italic f. It is likewise called jugulum, or collar bone, from its situation. It is about the size of the little finger, but longer, and being of a very spongy substance, is very liable to be fractured. In this, as in other long bones, we may distinguish a body and two extremities. The body is rather flattened than rounded. The anterior extremity is formed into a slightly convex head, which is nearly of a triangular shape. The inferior surface of the head is articulated with the sternum. The posterior extremity, which is flatter and broader than the other, is connected to a process of the scapula, called acromion. Both these articulations are secured by ligaments, and in that with the sternum we meet with a moveable cartilage, to prevent any injury from friction.

The clavicle serves to regulate the motions of the scapula, by preventing it from being brought too much forwards, or carried too far backwards. It affords origin to several muscles, and helps to cover and protect the subclavian vessels, which derive their name from their situation under this bone.

The scapula, or shoulder-blade, which is nearly of a triangular shape, is fixed to the posterior part of the pala. true ribs, somewhat in the manner of a buckler. It is of a very unequal thickness, and like all other broad flat bones, is somewhat cellular. Externally it is convex, and internally concave, to accommodate itself to the convexity of the ribs. We observe in this bone three unequal sides, which are thicker and stronger than the body of the bone, and are therefore termed its costa. The largest of the three, called also the basis, is turned towards the vertebrae. Another, which is less than the former, is below this; and the third, which is the least of the three, is at the upper part of the bone. Externally the bone is elevated into a considerable spine, which rising small at the basis of the scapula, becomes gradually higher and broader, and divides the outer surface of the bone into two fossae. The superior of these, which is the smallest, serves to lodge the supra spinatus muscle; and the inferior fossa, which is much larger than the other, gives origin to the infra spinatus. This spine terminates in a broad and flat process at the top of the shoulder, called the processus acromion, to which the clavicle is articulated. This process is hollowed at its lower part to allow a passage to the supra and infra spinati muscles. The scapula has likewise another considerable process at its upper part, which, from its resemblance to the beak of a bird, is called the coracoid process. From the outer side of this coracoid process, a strong ligament passes to the processus acromion, which prevents a luxation of the os humeri upwards. A third process begins by a narrow neck, and ends in a cavity called glenoid, for the connexion of the os humeri.

The scapula is articulated with the clavicle and os humeri, to which last it serves as a fulcrum; and by varying its position it affords a greater scope to the bones of the arm in their different motions. It likewise gives origin to several muscles, and posteriorly serves as a defence to the trunk.

2. Bones of the Arm.

The arm is commonly divided into two parts, which are articulated to each other at the elbow. The upper part retains the name of arm, properly so called, and the lower part is usually called the fore-arm.

The arm is composed of a single bone called os humeri. This bone, which is almost of a cylindrical shape, may be divided into its body and its extremities.

The upper extremity begins by a large, round, smooth head, which is admitted into the glenoid cavity of the scapula. On the upper and fore part of the bone there is a groove for lodging the long head of the biceps muscle of the arm; and on each side of the groove, at the upper end of the bone, there is a tubercle to which the spinati muscles are fixed.

The lower extremity has several processes and cavities. The principal processes are its two condyles, one exterior and the other interior, and of these the last is the largest. Between these two we observe two lateral protuberances, which, together with a middle cavity, The motions of the fore-arm are chiefly performed. At each side of the condyles, as well exteriorly as interiorly, there is another eminence which gives origin to several muscles of the hand and fingers. Posteriorly and superiorly, speaking with respect to the condyles, we observe a deep fossa which receives a considerable process of the ulna; and anteriorly and opposite to this fossa, we observe another, which is much less, and receives another process of the same bone.

The body of the bone has at its upper and anterior part a furrow which begins from behind the head of the bone, and serves to lodge the tendon of a muscle. The body of the os humeri is hollow through its whole length, and like all other long bones has its marrow.

This bone is articulated at its upper part to the scapula. This articulation, which allows motion every way, is surrounded by a capsular ligament that is sometimes torn in luxation, and becomes an obstacle to the easy reduction of the bone. Its lower extremity is articulated with the bones of the fore-arm.

The fore-arm is composed of two bones, the ulna and radius.

The ulna or elbow bone is much less than the os humeri, and becomes gradually smaller as it descends to the wrist. At its upper part it has two processes and two cavities. Of the two processes, the largest, which is situated posteriorly, and called the olecranon, is admitted into the posterior fossa of the os humeri. The other process is placed anteriorly, and is called the coronoid process. In bending the arm it enters into the anterior fossa of the os humeri. This process being much smaller than the other, permits the fore-arm to bend inwards; whereas the olecranon, which is shaped like a hook, reaches the bottom of its fossa in the os humeri as soon as the arm becomes straight, and will not permit the fore-arm to be bent backwards. The ligaments likewise oppose this motion.

Between the two processes we have described, there is a considerable cavity called the sigmoid cavity, divided into two fossae by a small eminence, which passes from one process to the other; it is by means of this cavity and the two processes, that the ulna is articulated with the os humeri by gingilimus.

At the bottom of the coronoid process anteriorly, there is a small sigmoid cavity, which serves for the articulation of the ulna with the radius.

The body of the ulna is of a triangular shape: Its lower extremity terminates by a small head and a little styloid process. The ulna is articulated above to the os humeri—both above and below to the radius, and to the wrist at its lower extremity. All these articulations are secured by means of ligaments. The chief use of this bone seems to be to support and regulate the motions of the radius.

The radius, which is so named from its supposed resemblance to the spoke of a wheel, is placed at the inside of the fore-arm. It is somewhat larger than the ulna, but not quite so long as that bone. Its upper part is cylindrical, hollowed superiorly to receive the Osteology. outer condyle of the os humeri. Laterally it is admitted into the little sigmoid cavity of the ulna, and the cylindrical part of the bone turns in this cavity in the motions of pronation and supination (L). This bone follows the ulna in flexion and extension, and may likewise be moved round its axis in any direction. The lower extremity of the radius is much larger and stronger than its upper part; the ulna, on the contrary, is smaller and weaker below than above; so that they serve to supply each other's deficiencies in both those parts.

On the external side of this bone, we observe a small cavity which is destined to receive the lower end of the ulna; and its lower extremity is formed into a large cavity, by means of which it is articulated with the bones of the wrist, and on this account it is sometimes called manus manus. It supports the two first bones of the wrist on the side of the thumb, whereas the ulna is articulated with that bone of the wrist which corresponds with the little finger.

Through the whole length both of this bone and the ulna, a ridge is observed which affords attachment to an interosseous ligament. This ligament fills up the space between the two bones.

3. Bones of the Hand.

The carpus or wrist consists of eight small bones of irregular shape, and disposed in two unequal rows. Those of the upper row are articulated with the bones of the fore-arm, and those of the lower one with the metacarpus.

The ancient anatomists described these bones numerically; Lyserus seems to have been the first who gave to each of them a particular name. The names he adopted are found on the figure of the bones, and are now pretty generally received, except the first, which instead of κεφαλοειδές (the name given to it by Lyserus, on account of its sinus, that admits a part of the os magnum), has by later writers been named Scaphoideus or Navicularis. This, which is the outermost of the upper row (considering the thumb as the outer side of the hand), is articulated with the radius; on its inner side it is connected with the os lunare, and below to the trapezium and trapezoides. Next to this is a smaller bone, called the os lunare; because its outer side, which is connected with the scaphoides, is shaped like a crescent. This is likewise articulated with the radius. On its inner side it joins the os cuneiforme; and anteriorly, the os magnum and os unciforme.

The os cuneiforme, which is the third bone in the upper row, is compared to a wedge, from its being broader above, at the back of the hand, than it is below. Posteriorly it is articulated with the ulna, and anteriorly with the os unciforme.

These three bones form an oblong articulating surface, covered by cartilage, by which the hand is connected with the fore-arm.

The os pisiforme, or pea-like bone, which is smaller than

(L) The motions of pronation and supination may be easily described. If the palm of the hand, for instance, is placed on the surface of a table, the hand may be said to be in a state of pronation; but if the back part of the hand is turned towards the table, the hand will be then in a state of supination.

Osteology, than the three just now described, though generally classed with the bones of the upper row, does not properly belong to either series, being placed on the under surface of the os cuneiforme, so as to project into the palm of the hand. The four bones of the second row correspond with the bones of the thumb and fingers; the first, second, and fourth, are from their shapes named trapezium, trapezoides, and unciforme; the third, from its being the largest bone of the carpus, is styled os magnum.

All these bones are convex towards the back, and slightly concave towards the palm of the hand; their articulating surfaces are covered with cartilages, and secured by many strong ligaments, particularly by two ligamentous expansions, called the external and internal annular ligaments of the wrist. The former extends in an oblique direction from the os pisiforme to the styloid process of the radius, and is an inch and a half in breadth; the latter or internal annular ligament is stretched from the os pisiforme and os unciforme, to the os scaphoides and trapezium. These annular ligaments likewise serve to bend down the tendons of the wrist and fingers.

The metacarpus consists of four bones, which support the fingers; externally they are a little convex, and internally somewhat concave, where they form the palm of the hand. They are hollow, and of a cylindrical shape.

At each extremity they are a little hollowed for their articulation; superiorly with the bones of the carpus, and inferiorly with the first phalanx of the fingers, in the same manner as the several phalanges of the fingers are articulated with each other.

The five fingers of each hand are composed of fifteen bones, disposed in three ranks called phalanges: The bones of the first phalanx, which are articulated with the metacarpus, are the largest, and those of the last phalanx the smallest. All these bones are larger at their extremities than in their middle part.

We observe at the extremities of the bones of the carpus, metacarpus, and fingers, several inequalities that serve for their articulation with each other; and these articulations are strengthened by means of the ligaments which surround them.

It will be easily understood that this multiplicity of bones in the hand (for there are 27 in each hand) is essential to the different motions we wish to perform. If each finger was composed only of one bone instead of three, it would be impossible for us to grasp anything.

§ 2. Of the Lower Extremities.

Each lower extremity is divided into four parts, viz. the os femoris, or thigh bone; the rotula, or knee-pan; the leg; and the foot.

1. Of the Thigh.

The thigh is composed only of this bone, which is the largest and strongest we have. It will be necessary to distinguish its body and extremities: Its body, which is of a cylindrical shape, is convex before and concave behind, where it serves to lodge several muscles. Throughout two-thirds of its length we observe a ridge, called linea aspera, which originates from the trochanters, and after running for some way downwards, divides into two branches, that terminate in the tuberosities at the lower extremity of the bone.

At its upper extremity we must describe the neck and smooth head of the bone, and likewise two considerable processes: The head, which forms the greater portion of a sphere unequally divided, is turned inwards, and received into the great cotyloid cavity of the os innominatum. At this part of the bone there is a little fossa to be observed, to which the round ligament is attached, and which we have already described as tending to secure the head of this bone in the great acetabulum. The neck is almost horizontal, considered with respect to its situation with the body of the bone. Of the two processes, the external one, which is the largest, is called trochanter major; and the other, which is placed on the inside of the bone, trochanter minor. They both afford attachment to muscles. The articulation of the os femoris with the trunk is strengthened by means of a capsular ligament, which adheres everywhere round the edge of the great cotyloid cavity of the os innominatum, and surrounds the head of the bone.

The os femoris moves upon the trunk in every direction.

At the lower extremity of the bone are two processes called the condyles, and an intermediate smooth cavity, by means of which it is articulated with the leg by gin-glium.

All round the under end of the bone there is an irregular surface where the capsular ligament of the joint has its origin, and where blood-vessels go into the substance of the bone.

Between the condyles there is a cavity posteriorly, in which the blood-vessels and nerves are placed, secure from the compression to which they would otherwise be exposed in the action of bending the leg, and which would not fail to be hurtful.

At the side of each condyle externally, there is a tuberosity, from whence the lateral ligaments originate, which are extended down to the tibia.

A ligament likewise arises from each condyle posteriorly. One of these ligaments passes from the right to the left, and the other from the left to the right, so that they intersect each other, and for that reason are called the cross ligaments.

The lateral ligaments prevent the motion of the leg upon the thigh to the right or left, and the cross ligaments, which are also attached to the tibia, prevent the latter from being brought forwards.

In new born children all the processes of this bone are cartilaginous.

2. The Rotula, or Knee-pan.

The rotula, patella, or knee-pan, as it is differently called, is a flat bone about four or five inches in circumference, and is placed at the fore part of the joint of the knee. In its shape it is somewhat like the common figure of the heart, with its point downwards.

It is thinner at its edge than in its middle part; at its forepart it is smooth and somewhat convex; its posterior surface, which is more unequal, affords an elevation in the middle which is admitted between the two condyles of the os femoris.

This bone is retained in its proper situation by a strong ligament which everywhere surrounds it, and adheres adheres both to the tibia and os femoris; it is likewise firmly connected with the tibia by means of a strong tendinous ligament of an inch in breadth, and upwards of two inches in length, which adheres to the lower part of the patella, and to the tuberosity at the upper end of the tibia. On account of this connexion, it is very properly considered as an appendage to the tibia, which it follows in all its motions, so as to be to it what the olecranon is to the ulna. There is this difference, however, that the olecranon is a fixed process; whereas the patella is moveable, being capable of sliding from above downwards and from below upwards. This mobility is essential to the rotatory motion of the leg.

In very young children this bone is entirely cartilaginous.

The principal use of the patella seems to be to defend the articulation of the knee from external injury; it likewise tends to increase the power of the extensor muscles of the leg, by removing their direction farther from the centre of motion in the manner of a pulley.

3. Of the Leg.

The leg is composed of two bones: Of these the inner one, which is the largest; is called tibia; the other is much smaller, and named fibula.

The tibia, which is so called from its resemblance to the musical pipe of the ancients, has three surfaces, and is not very unlike a triangular prism. Its posterior surface is the broadest; anteriorly it has a considerable ridge called the shin, between which and the skin there are no muscles. At the upper extremity of this bone are two surfaces, a little concave, and separated from each other by an intermediate elevation. The two little cavities receive the condyles of the os femoris, and the eminence between them is admitted into the cavity which we spoke of as being between the two condyles; so that this articulation affords a specimen of the complete ginglymus. Under the external edge of the upper end of this bone is a circular flat surface, which receives the head of the fibula.

At the lower and inner portion of the tibia, we observe a considerable process called malleolus internus. The basis of the bone terminates in a large transverse cavity, by which it is articulated with the uppermost bone of the foot. It has likewise another cavity at its lower end and upper side, which is somewhat oblong, and receives the lower end of the fibula.

The tibia is hollow through its whole length.

The fibula is a small long bone situated on the outside of the tibia. Its superior extremity does not reach quite so high as the upper part of the tibia, but its lower end descends somewhat lower. Both above and below, it is articulated with the tibia by means of the lateral cavities we noticed in our description of that bone.

Its lower extremity is stretched out into a coronoid process, which is flattened at its inside, and is convex externally, forming what is called the malleolus externus, or outer ankle. This is rather lower than the malleolus internus of the tibia.

Vol. II. Part I.

The body of this bone, which is irregularly triangular, is a little hollow at its internal surface, which is turned towards the tibia; and it affords like that bone, through its whole length, attachment to a ligament, which from its situation is called the interosseous ligament.

4. Of the Foot.

The foot consists of the tarsus, metatarsus, and toes.

The tarsus is composed of seven bones, viz. the astragalus, os calcis, os naviculare, os cuboideum, and three others called cuneiform bones.

The astragalus is a large bone with which both the tibia and fibula are articulated. It is the uppermost bone of the foot; it has several surfaces to be considered; its upper, and somewhat posterior part, which is smooth and convex, is admitted into the cavity of the tibia. Its lateral parts are connected with the malleoli of the two bones of the legs; below, it is articulated with the os calcis, and its anterior surface is received by the os naviculare. All these articulations are secured by means of ligaments.

The os calcis, or calcaneum, which is of a very irregular figure, is the largest bone of the foot. Behind, calcis, it is formed into a considerable tuberosity, called the heel; without this tuberosity, which supports us in an erect posture, and when we walk, we should be liable to fall backwards.

On the internal surface of this bone, we observe a considerable sinuosity, which affords a passage to the tendon of a muscle; and to the posterior part of the os calcis, a strong tendinous cord, called tendo achillis (M), is attached, which is formed by the tendons of several muscles united together. The articulation of this with the other bones is secured by means of ligaments.

The os naviculare, or scaphoides (for these two terms of the os have the same signification), is so called on account of its resemblance to a little bark. At its posterior part, which is concave, it receives the astragalus; anteriorly it is articulated with the cuneiform bones, and laterally it is connected with the os cuboideum.

The os cuboideum forms an irregular cube. Posteriorly it is articulated with the os calcis; anteriorly it supports the two last bones of the metatarsus, and laterally it joins the third cuneiform bone and the os naviculare.

Each of the ossa cuneiformia, which are three in number, resembles a wedge, and from this similitude their name is derived. They are placed next to the metatarsus by the sides of each other, and are usually distinguished into os cuneiforme externum, medium or minimum, and internum or maximum. The superior surface of these bones, from their wedge-like shape, is broader than that which is below, where they help to form the sole of the foot; posteriorly they are united to the os naviculare, and anteriorly they support the three first metatarsal bones.

When these seven bones composing the tarsus are viewed together in the skeleton, they appear convex above, where they help to form the upper part of the foot; and concave underneath, where they form the hollow

(m) This tendon is sometimes ruptured by jumping, dancing, or other violent efforts.

The hollow of the foot, in which the vessels, tendons, and nerves of the foot, are placed secure from pressure.

They are united to each other by very strong ligaments, and their articulation with the foot is secured by a capsular and two lateral ligaments; each of the latter is covered by an annular ligament of considerable breadth and thickness, which serves to bind down the tendons of the foot, and at the same time to strengthen the articulation.

The os cuneiforme externum is joined laterally to the os cuboides.

These bones complete our account of the tarsus. Though what we have said of this part of the osteology has been very simple and concise, yet many readers may not clearly understand it; but if they will be pleased to view these bones in their proper situation in the skeleton, all that we have said of them will be easily understood.

The metatarsus is made up of five bones, whereas the metacarpus consists only of four. The cause of this difference is, that in the hand the last bone of the thumb is not included among the metacarpal bones; whereas in the foot the great toe has only two bones. The first of these bones supports the great toe, and is much larger than the rest, which nearly resemble each other in size.

These bones are articulated by one extremity with the cuneiform bones and the os cuboides, and by their other end with the toes.

Each of the toes, like the fingers, consists of three bones, except the great toe, which is formed of two bones. Those of the other four are distinguished into three phalanges. Although the toes are more confined in their motion than the fingers, yet they appear to be perfectly fitted for the purposes they are designed for. In walking, the toes bring the centre of gravity perpendicular to the advanced foot; and as the soles of the feet are naturally concave, we can at pleasure increase the concavity, and form a kind of vault, which adjusts itself to the different inequalities that occur to us in walking; and which, without this mode of arrangement, would incommode us exceedingly, especially when bare-footed.

§ 4. Of the Osse Sesamoidea.

Besides the bones we have already described, there are several small ones that are met with only in the adult skeleton, and in persons who are advanced in life; which, from their supposed general resemblance to the seeds of the sesamum, are called osse sesamoidea. They are commonly to be seen at the first joint of the great toe, and sometimes at the joints of the thumb; they are likewise now and then to be found at the lower extremity of the fibula, upon the condyles of the thigh-bone, under the os cuboides of the tarsus, and in other parts of the body. Their size and number seem constantly to be increased by age and hard labour; and as they are generally found in situations where tendons and ligaments are most exposed to the action of muscles, they are now generally considered as ossified portions of ligaments or tendons.

The upper surface of these bones is usually convex, and adherent to the tendon that covers it; the side which is next to the joint is smooth and flat. Though their formation is accidental, yet they seem to be of some use, by raising the tendons farther from the centre of motion, and consequently increasing the power of the muscles. In the great toe and thumb they are likewise useful, by forming a groove for the flexor tendons.

EXPLANATION OF THE PLATES OF OSTEOLGY.

PLATE XXI.

Fig. 1. A Front View of the Male Skeleton.

A, The os frontis. B, The os parietale. C, The coronal suture. D, The squamos part of the temporal bones. E, The squamos suture. F, The zygoma. G, The mastoid process. H, The temporal process of the sphenoid bone. I, The orbit. K, The os maxillae. L, The os maxillare superius. M, Its nasal process. N, The os naso. O, The os unguis. P, The maxilla inferior. Q, The teeth, which are sixteen in number in each jaw. R, The seven cervical vertebrae, with their intermediate cartilages. S, Their transverse processes. T, The twelve dorsal vertebrae, with their intermediate cartilages. U, The five lumbar vertebrae. V, Their transverse processes. W, The upper part of the os sacrum. X, Its lateral parts. The holes seen on its fore part are the passages of the undermost spinal nerves and small vessels. Opposite to the holes, the marks of the original divisions of the bone are seen. Y, The os ilium. Z, Its crest or spine. a, The anterior spinous processes. b, The brim of the pelvis. c, The ischiatric niche. d, The os ischium. e, Its tuberosity. f, Its spinous process. g, Its crus. h, The foramen thyroideum. i, The os pubis. k, The symphysis pubis. l, The crus pubis. m, The acetabulum. n, The seventh or last true rib. o, The twelfth or last false rib. p, The upper end of the sternum. q, The middle piece. r, The upper end, or cartilago ensiformis. s, The clavicle. t, The internal surface of the scapula. u, Its acromion. v, Its coracoid process. w, Its cervix. x, The glenoid cavity. y, The os humeri. z, Its head, which is connected to the glenoid cavity. 1, Its external tubercle. 2, Its internal tubercle. 3, The groove for lodging the long head of the biceps muscle of the arm. 4, The internal condyle. 5, The external condyle. Between 4 and 5, the trochlea. 6, The radius. 7, Its head. 8, Its tubercle. 9, The ulna. 10, Its coronoid process. 11, 12, 13, 14, 15, 16, 17, 18, The carpus; composed of os naviculare, os lunare, os cuneiforme, os pisiforme, os trapezium, os trapezoideum, os magnum, os unciforme. 19, The five bones of the metacarpus. 20, The two bones of the thumb. 21, The three bones of each of the fingers. 22, The os femoris. 23, Its head. 24, Its cervix. 25, The trochanter major. 26, The trochanter minor. 27, The internal condyle. 28, The external condyle. 29, The rotula. 30, The tibia. 31, Its head. 32, Its tubercle. 33, Its spine. 34, The malleolus internus. 35, The fibula. 36, Its head. 37, The malleolus externus. The tarsus is composed of; 38, The astragalo- Fig. 2. A Front View of the Skull.

A, The os frontis. B, The lateral part of the os frontis, which gives origin to part of the temporal muscle. C, The superciliary ridge. D, The superciliary hole through which the frontal vessels and nerves pass. EE, The orbital processes. F, The middle of the transverse suture. G, The upper part of the orbit. H, The foramen opticum. I, The foramen lacrimum. K, The inferior orbital fissure. L, The os uncus. M, The os naso. N, The os maxillare superior. O, Its nasal process. P, The external orbital hole through which the superior maxillary vessels and nerves pass. Q, The os malle. R, A passage for small vessels into, or out of, the orbit. S, The under part of the left nostril. T, The septum narium. U, The os spongiosum superius. V, The os spongiosum inferius. W, The edge of the alveoli, or bony sockets, for the teeth. X, The maxilla inferior. Y, The passage for the inferior maxillary vessels and nerves.

Fig. 3. A Side View of the Skull.

A, The os frontis. B, The coronal suture. C, The os parietale. D, An arched ridge which gives origin to the temporal muscle. E, The squamous suture. F, The squamous part of the temporal bone; and farther forwards, the temporal process of the sphenoid bone. G, The zygomatic process of the temporal bone. H, The zygomatic suture. I, The mastoid process of the temporal bone. K, The meatus auditorius externus. L, The orbital plate of the frontal bone, under which is seen the transverse suture. M, The pars plana of the ethmoid bone. N, The os uncus. O, The right os naso. P, The superior maxillary bone. Q, Its nasal process. R, The two dentes incisores. S, The dens caninus. T, The two small molares. U, The three large molares. V, The os malle. W, The lower jaw. X, Its angle. Y, The coronoid process. Z, The condyloid process, by which the jaw is articulated with the temporal bone.

Fig. 4. The Posterior and Right side of the Skull.

A, The os frontis. BB, The ossa parietalia. C, The sagittal suture. D, The parietal hole, through which a small vein runs to the superior longitudinal sinus. EE, The lambdoid suture. FF, Ossa trigonata. G, The os occipitis. H, The squamous part of the temporal bone. I, The mastoid process. K, The zygoma. L, The os malle. M, The temporal part of the sphenoid bone. N, The superior maxillary bone and teeth.

Fig. 5. The External Surface of the Os Frontis.

A, The convex part. B, Part of the temporal fossa. C, The external angular process. D, The internal angular process. E, The nasal process. F, The superciliary arch. G, The superciliary hole. H, The orbital plate.

Fig. 6. The Internal Surface of the Os Frontis.

AA, The serrated edge which assists to form the coronal suture. B, The external angular process. C, The internal angular process. D, The nasal process. E, The orbital plate. F, The cells which correspond osteology with those of the ethmoid bone. G, The passage from the frontal sinus. H, The opening which receives the cribriform plate of the ethmoid bone. I, The cavity which lodges the fore part of the brain. K, The spine to which the falx is fixed. L, The groove which lodges the superior longitudinal sinus.

Plate XXII.

Fig. 1. A Back View of the Skeleton.

AA, The ossa parietalia. B, The sagittal suture. C, The lambdoid suture. D, The occipital bone. E, The squamos suture. F, The mastoid process of the temporal bone. G, The os malic. H, The palate plates of the superior maxillary bones. I, The maxilla inferior. K, The teeth of both jaws. L, The seven cervical vertebrae. M, Their spinous processes. N, Their transverse and oblique processes. O, The last of the twelve dorsal vertebrae. P, The fifth or last lumbar vertebra. Q, The transverse processes. R, The oblique processes. S, The spinous processes. T, The upper part of the os sacrum. U, The posterior holes which transmit small blood-vessels and nerves. V, The under part of the os sacrum which is covered by a membrane. W, The os coccygis. X, The os ilium. Y, Its spine or crest. Z, The ischiatric niche. a, The os ischium. b, Its tuberosity. c, Its spine. d, The os pubis. e, The foramen thyroideum. f, The seventh or last true rib. g, The twelfth or last false rib. h, The clavicle. i, The scapula. k, Its spine. l, Its acromion. m, Its cervix. n, Its superior costa. o, Its posterior costa. p, Its inferior costa. q, The os humeri. r, The radius. s, The ulna. t, Its olecranon. u, All the bones of the carpus, excepting the os pisiforme, which is seen in Plate XXI. fig. 1. v, The five bones of the metacarpus. w, The two bones of the thumb. x, The three bones of each of the fingers. y, The two sesamoid bones at the root of the left thumb. z, The os femoris. 1, The trochanter major. 2, The trochanter minor. 3, The linea aspera. 4, The internal condyle. 5, The external condyle. 6, The semilunar cartilages. 7, The tibia. 8, The malleolus internus. 9, The fibula. 10, The malleolus externus. 11, The tarsus. 12, The metatarsus. 13, The toes.

Fig. 2. The External Surface of the Left Os Parietal.

A, The convex smooth surface. B, The parietal hole. C, An arch made by the beginning of the temporal muscle.

Fig. 3. The Internal Surface of the same Bone.

A, Its superior edge, which, joined with the other, forms the sagittal suture. B, The anterior edge, which assists in the formation of the coronal suture. C, The inferior edge for the squamous suture. D, The posterior edge for the lambdoid suture. E, A depression made by the lateral sinus. FF, The prints of the arteries of the dura mater.

Fig. 4. The External Surface of the Left Os Tempororum.

A, The squamous part. B, The mastoid process. C, The zygomatic process. D, The styloid process. E, The petrosal process. F, The meatus auditorius externus.

Osteology. externus. G, The glenoid cavity for the articulation of the lower jaw. H, The foramen stylo-mastoideum for the pertia dura of the seventh pair of nerves. I, Passages for blood vessels into the bone. K, The foramen mastoideum through which a vein goes to the lateral sinus.

Fig. 5. The Internal Surface of the Left Os Temporum.

A, The squamous part; the upper edge of which assists in forming the squamous suture. B, The mastoid process. C, the styloid process. D, The pars petrosa. E, The entry of the seventh pair, or auditory nerve. F, The fossa, which lodges a part of the lateral sinus. G, The foramen mastoideum.

Fig. 6. The External Surface of the Osseous Circle, which terminates the meatus auditorius externus.

A, The anterior part. B, A small part of the groove in which the membrana tympani is fixed.

N.B. This, with the subsequent bones of the ear, are here delineated as large as the life.

Fig. 7. The Internal Surface of the Osseous Circle.

A, The anterior part. B, The groove in which the membrana tympani is fixed.

Fig. 8. The situation and connexion of the Small Bones of the Ear.

A, The malleus. B, The incus. C, The os orbiculare. D, The stapes.

Fig. 9. The Malleus, with its Head, Handle, and Small Processes.

Fig. 10. The Incus, with its Body, Superior and Inferior Branches.

Fig. 11. The Os Orbiculare.

Fig. 12. The Stapes, with its Head, Base, and two Crus.

Fig. 13. An Internal View of the Labyrinth of the Ear.

A, The hollow part of the cochlea, which forms a share of the meatus auditorius internus. B, The vestibulum. CCC, The semicircular canals.

Fig. 14. An External View of the Labyrinth.

A, The semicircular canals. B, The fenestra ovalis which leads into the vestibulum. C, The fenestra rotunda which opens into the cochlea. D, The different turns of the cochlea.

Fig. 15. The Internal Surface of the Os Sphenoides.

AA, The temporal processes. BB, The pterygoid processes. CC, The spinous processes. DD, The anterior clinoid processes. E, The posterior clinoid process. F, The anterior process which joins the ethmoid bone. G, The sella turcica for lodging the glandula pituitaria. H, The foramen opticum. K, The foramen lacerum. L, The foramen rotundum. M, The foramen ovale. N, The foramen spinale.

Fig. 16. The External Surface of the Os Sphenoides.

AA, The temporal processes. BB, The pterygoid processes. CC, The spinous processes. D, The processus azygos. E, The small triangular processes which grow from the body of the bone. FF, The orifices of the sphenoidal sinuses. G, The foramen lacerum. H, The foramen rotundum. I, The foramen ovale. K, The foramen pterygoideum.

Fig. 17. The External View of the Os Ethmoides.

A, The nasal lamella. BB, The grooves between the nasal lamella and ossa spongiosa superiores. CC, The ossa spongiosa superiores. DD, The sphenoid cornua. See Fig. 16. E.

Fig. 18. The Internal View of the Os Ethmoides.

A, The crista galli. B, The cribriform plate, with the different passages of the olfactory nerves. CC, Some of the ethmoidal cells. D, The right os planum. EE, The sphenoidal cornua.

Fig. 19. The Right Sphenoidal Cornu.

Fig. 20. The Left Sphenoidal Cornu.

Fig. 21. The External Surface of the Os Occipitis.

A, The upper part of the bone. B, The superior arched ridge. C, The inferior arched ridge. Under the arches are prints made by muscles of the neck. DD, The two condyloid processes which articulate the head with the spine. E, The unciform process. F, The foramen magnum through which the spinal marrow passes. GG, The posterior condyloid foramina which transmit veins into the lateral sinuses. HH, The foramina lingualia for the passage of the ninth pair of nerves.

Fig. 22. The Internal Surface of the Os Occipitis.

AA, The two sides which assist to form the lambdoid suture. B, The point of the unciform process where it joins the sphenoid bone. CC, The prints made by the posterior lobes of the brain. DD, Prints made by the lobes of the cerebellum. E, The cruciform ridge for the attachment of the processes of the dura mater. F, The course of the superior longitudinal sinuses. GG, The course of the two lateral sinuses. H, The foramen magnum. II, The posterior condyloid foramina.

PLATE XXIII.

Fig. 1. A Side View of the Skeleton.

AA, The ossa parietalia. B, The sagittal suture. C, The os occipitis. DD, The lambdoid suture. E, The squamos part of the temporal bone. F, The mastoid process. G, The meatus auditorius externus. H, The os frontis. I, The os maxillae. K, The os maxillare superius. L, The maxilla inferior. M, The teeth of both jaws. N, The seventh or last cervical vertebra. O, The spinous processes. P, Their transverse and oblique processes. Q, The twelfth or last dorsal vertebra. R, The fifth or last lumbar vertebra. S, The spinous processes. T, Openings between the vertebrae for the passage of the spinal nerves. U, The under end of the os sacrum. V, The os coccygis. W, The os ilium. X, The anterior spinous processes. Y, The posterior spinous processes. Z, The ischiatic niche. a, The right os ilium. b, The ossa pubis. c, The tuberosity of the left os ischium. d, The scapula. e, Its spine. f, The os humeri. g, The radius. h, The ulna. i, The carpus. k, The metacarpal bone of the thumb. l, The metacarpal bones of the fingers. m, The two bones of the thumb. n, The three bones of each of the fingers. o, The os femoris. Fig. 2. A View of the Internal Surface of the Base of the Skull.

AAA, The two tables of the skull with the diploe. BB, The orbital plates of the frontal bone. C, The crista galli, with the cribiform plate of the ethmoidal bone on each side of it, through which the first pair of nerves pass. D, The cuneiform process of the occipital bone. E, The cruciform ridge. F, The foramen magnum for the passage of the spinal marrow. G, The zygoma, made by the joining of the zygomatic processes of the os temporum and os maxillae. H, The pars squamosa of the os temporum. I, The pars mammillaris. K, The pars petrosa. L, The temporal process of the sphenoid bone. MM, The anterior clinoid processes. N, The posterior clinoid process. O, The sella turcica. P, The foramen opticum, for the passage of the optic nerve and ocular artery of the left side. Q, The foramen lacrimale, for the third, fourth, sixth, and first of the fifth part of nerves and ocular vein. R, The foramen rotundum for the second of the fifth pair. S, The foramen ovale, for the third of the fifth pair. T, The foramen spinale, for the principal artery of the dura mater. U, The entry of the auditory nerve. V, The passage for the lateral sinus. W, The passage of the eighth pair of nerves. X, The passage of the ninth pair.

Fig. 3. A View of the External Surface of the Base of the Skull.

A, The two dentes incisores of the right side B, The dens caninus. C, The two small molares. D, The three large molares. E, The foramen incisivum, which gives passage to small blood-vessels and nerves. F, The palate plates of the ossa maxillaria and palati, joined by the longitudinal and transverse palate sutures. G, The foramen palatinum posterius, for the palatine vessels and nerves. H, The os maxillare superius of the right side. I, The os maxillae. K, The zygomatic process of the temporal bone. L, The posterior extremity of the os spongiosum. M, The posterior extremity of the vomer, which forms the back part of the septum nasi. N, The pterygoid process of the right side of the sphenoid bone. OO, The foramina ovalia. PP, The foramina spinalia. QQ, The passages of the internal carotid arteries. R, A hole between the point of each pars petrosa and cuneiform process of the occipital bone, which is filled up with a ligamentous substance in the recent subject. S, The passage of the left lateral sinus. T, The posterior condyloid foramen of the left side. U, The foramen mastoideum. V, The foramen magnum. W, The inferior orbital fissure. X, The glenoid cavity, for the articulation of the lower jaw. Y, The squamous part of the temporal bone. Z, The mastoid process, at the inner side of which is a fossa for the posterior belly of the digastric muscle. a, The styloid process. b, The meatus auditorius externus. c, The left condyle of the occipital bone. d, The perpendicular occipital spine. ee, The inferior horizontal ridge of the occipital bone. ff, The superior horizontal ridge, which is opposite to the crucial ridge where the longitudinal sinus divides to form the lateral sinuses. ggg, The lambdoid suture. h, The left squamous suture. i, The parietal bone.

Fig. 4. The Anterior Surface of the Os Maxillare Superius of the left side.

A, The nasal process. B, The orbital plate. C, The unequal surface which joins the os maxillae. D, The external orbital hole. E, The opening into the nostril. F, The palate plate. G, The maxillary tuberosity. H, Part of the os palati. I, The two dentes incisores. K, The dens caninus. L, The two small dentes molares. M, The three large dentes molares.

Fig. 5. The Posterior Surface of the Os Maxillare Superius.

AA, Their cavity, which forms part of the arch of the nose. BB, Their ridge or spine, which projects a little to be fixed to the fore part of the septum nasi.

Fig. 6. The External Surface of the Os Maxillare Superius and Os Palati.

A, The nasal process. BB, Eminences for the connexion of the spongiosum inferius. D, The under end of the lachrymal groove. E, The antrum maxillare. F, The nasal spine, between which and B is the cavity of the nostril. G, The palate plate. H, The orbital part of the os palati. I, The nasal plate. K, The suture which unites the maxillary and palate bones. L, The pterygoid process of the palate bone.

Fig. 7. The Internal Surface of the Os Maxillare Superius and Os Palati.

A, The nasal process. BB, Eminences for the connexion of the spongiosum inferius. D, The under end of the lachrymal groove. E, The antrum maxillare. F, The nasal spine, between which and B is the cavity of the nostril. G, The palate plate. H, The orbital part of the os palati. I, The nasal plate. K, The suture which unites the maxillary and palate bones. L, The pterygoid process of the palate bone.

Fig. 8. The External Surface of the right Os Unguis.

A, The orbital part. B, The lachrymal part. C, The ridge between them.

Fig. 9. The Internal Surface of the right Os Unguis.

This side of the bones has a furrow opposite to the external ridge; all behind this is irregular, where it covers part of the ethmoidal cells.

Fig. 10. The External Surface of the left Os Malae.

A, The superior orbital process. B, The inferior orbital process. C, The malar process. D, The zygomatic process. E, The orbital plate. F, A passage for small vessels into or out of the orbit.

Fig. 11. The Internal Surface of the left Os Malae.

A, The superior orbital process. B, The inferior orbital process. C, The malar process. D, The zygomatic process. E, The internal orbital plate or process.

Fig. 12. The External Surface of the right Os Spongiosum Inferius.

A, The anterior part. B, The hook-like process for covering part of the antrum maxillare. C, A small process which covers part of the under end of the lachrymal groove. D, The inferior edge turned a little outwards.

Osteology.

Fig. 13. The Internal Surface of the Os Spongiosum Inferius. A, The anterior extremity. B, The upper edge which joins the superior maxillary and palate bones.

Fig. 14. The Posterior and External Surface of the right Os Palati. A, The orbital process. B, The nasal lamella. C, The pterygoid process. D, The palate process.

Fig. 15. The Anterior and External Surface of the right Os Palati. A, The orbital process. B, An opening through which the lateral nasal vessels and nerves pass. C, The nasal lamella. D, The pterygoid process. E, The posterior edge of the palate process for the connexion of the velum palati. F, The inner edge by which the two ossa palatini are connected.

Fig. 16. The right side of the Vomer. A, The upper edge which joins the nasal lamella of the ethmoid bone and the middle cartilage of the nose. B, The inferior edge which is connected to the superior maxillary and palate bones. C, The superior and posterior part which receives the processus azygos of the sphenoid bone.

Fig. 17. The Maxilla Inferior. A, The chin. B, The base and left side. C, The angle. D, The coronoid process. E, The condyloid process. F, The beginning of the inferior maxillary canal of the right side, for the entry of the nerve and blood vessels. G, The termination of the left canal. H, The two dentes incisores. I, The dens caninus. K, The two small molares. L, The three large molares.

Fig. 18. The different classes of the Teeth. 1, 2, A fore and back view of the two anterior dentes incisores of the lower jaw. 3, 4, Similar teeth of the upper jaw. 5, 6, A fore and back view of the dentes canini. 7, 8, The anterior dentes molares. 9, 10, 11, The posterior dentes molares. 12, 13, 14, 15, 16, Unusual appearances in the shape and size of the teeth.

Fig. 19. The External Surface of the Os Hyoides. A, The body. BB, The cornua. CC, The appendices.

Plate XXIV.

Fig. 1. A Posterior View of the Sternum and Clavicles, with the Ligament connecting the Clavicles to each other. a, The posterior surface of the sternum. bb, The broken ends of the clavicles. cccc, The tubercles near the extremity of each clavicle. d, The ligament connecting the clavicles.

Fig. 2. A Fore View of the Left Scapula, and of a half of the Clavicle, with their Ligaments. a, The spine of the scapula. b, The acromion. c, The inferior angle. d, Inferior costa. e, Cervix. f, Glenoid cavity, covered with cartilage for the arm bone. gg, The capsular ligament of the joint. h, Coracoid process. i, The broken end of the clavicle. k, Its extremity joined to the acromion. l, A ligament coming out single from the acromion to the coracoid process. m, A ligament coming out single from the acromion, and dividing it into two, which are fixed to the coracoid process.

Fig. 3. The Joint of the Elbow of the Left Arm, with the Ligaments. a, The os humeri. b, Its internal condyle. cc, The two prominent parts of its trochlea appearing through the capsular ligament. d, The ulna. e, The radius. f, The part of the ligament including the head of the radius.

Fig. 4. The Bones of the Right Hand, with the Palm in view. a, The radius. b, The ulna. c, The scaphoid bone of the carpus. d, The os lunare. e, The os cuneiforme. f, The os pisiforme. g, Trapezium. h, Trapezoides. i, Capitatum. k, Unciforme. l, The four metacarpal bones of the fingers. m, The first phalanx. n, The second phalanx. o, The third phalanx. p, The metacarpal bone of the thumb. q, The first joint. r, The second.

Fig. 5. The Posterior View of the Bones of the Left Hand. The explication of Fig. 4 serves for this figure; the same letters pointing out the same bones, though in a different view.

Fig. 6. The Upper extremity of the Tibia, with the Semilunar Cartilages of the Joint of the Knee, and some Ligaments. a, The strong ligament which connects the rotula to the tubercle of the tibia. bb, The parts of the extremity of the tibia, covered with cartilage, which appear within the semilunar cartilages. cc, The semilunar cartilages. d, The two parts of what is called the cross ligament.

Fig. 7. The Posterior View of the Joint of the Right Knee. a, The os femoris cut. b, Its internal condyle. c, Its external condyle. d, The back part of the tibia. e, The superior extremity of the fibula. f, The edge of the internal semilunar cartilage. g, An oblique ligament. h, A larger perpendicular ligament. i, A ligament connecting the femur and fibula.

Fig. 8. The Anterior View of the Joint of the Right Knee. b, The internal condyle. c, Its external condyle. d, The part of the os femoris, on which the patella moves. e, A perpendicular ligament. ff, The two parts of the crucial ligaments. gg, The edges of the two moveable semilunar cartilages. h, The tibia. i, The strong ligament of the patella. k, The back part of it where the fat has been dissected away. l, The external depression. m, The internal one. n, The cat tibia.

Fig. 9. A View of the Inferior Part of the Bones of the Right Foot. a, The great knob of the os calcis. b, A prominence on its outside. c, The hollow for the tendons, nerves, and blood vessels. d, The anterior extremity of the os calcis. e, Part of the astragalus. f, Its head covered with cartilage. g, The internal promi-

Fig. 10. The Inferior Surface of the two large Sesamoid Bones at the first joint of the Great Toe.

Fig. 11. The Superior View of the Bones of the Right Foot. a, b, as in fig. 9. c, The superior head of the astragalus. d, &c. as in fig. 9.

Fig. 12. The View of the Sole of the Foot, with its Ligaments. a, The great knob of the os calcis. b, the hollow for the tendons, nerves, and blood-vessels. c, The sheaths of the flexores pollicis and digitorum longi opened. d, The strong cartilaginous ligament supporting the head of the astragalus. e, h, Two ligaments which unite into one, and are fixed to the metatarsal bone of the great toe. f, A ligament from the knob of the os calcis to the metatarsal bone of the little toe. g, A strong triangular ligament, which supports the bones of the tarsus. i, The ligaments of the joints of Osteology, the five metatarsal bones.

Fig. 13. a, The head of the thigh-bone of a child. b, The ligamentum rotundum connecting it to the acetabulum. c, The capsular ligament of the joint with its arteries injected. d, The numerous vessels of the mucilaginous gland injected.

Fig. 14. The Back View of the Cartilages of the Larynx, with the Os Hyoides. a, The posterior part of the base of the os hyoides. bb, Its cornua. c, The appendix of the right side. d, A ligament sent out from the appendix of the left side, to the styloid process of the temporal bone. e, The union of the base with the left cornua. ff, The posterior sides of (g) the thyroid cartilages. hh, Its superior cornua. ii, Its inferior cornua. k, The cricoid cartilage. ll, The arytenoid cartilages. m, The entry into the lungs, named glottis. n, The epiglottis. oo, The superior cartilages of the trachea. p, Its ligamentous back part.

Fig. 15. The Superior Concave Surface of the Sesamoid Bones at the first joint of the Great Toe, with their Ligaments. a, Three sesamoid bones. b, The ligamentous substance in which they are formed.

CHAP. II. OF THE SOFT PARTS IN GENERAL.

OF THE COMMON INTEGUMENTS WITH THEIR APPENDAGES; AND OF THE MUSCLES.

ANATOMICAL writers usually proceed to a description of the muscles after having finished the osteology; but we shall deviate a little from the common method, with a view to describe every thing clearly and distinctly, and to avoid a tautology which would otherwise be unavoidable. All the parts of the body are so intimately connected with each other, that it seems impossible to convey a just idea of any one of them, without being in some measure obliged to say something of others; and on this account we wish to mention in this place the names and situation of the principal viscera of the body, that when mention is hereafter made of any one of them in the course of the work, the reader may at least know where they are placed.

After this little digression, the common integuments, and after them the muscles, will be described; we then propose to enter into an examination of the several viscera, and their different functions. In describing the brain, occasion will be taken to speak of the nerves and animal spirits. The circulation of the blood will follow the anatomy of the heart, and the secretions and other matters will be introduced in their proper places.

The body is divided into three great cavities. Of these the uppermost is formed by the bones of the cranium, and encloses the brain and cerebellum.

The second is composed of the vertebre of the back, the sternum, and true ribs, with the additional assistance of muscles, membranes, and common integuments, and is called the thorax.—It contains the heart and lungs.

The third, and inferior cavity, is the abdomen. It is separated from the thorax by means of the diaphragm, and is formed by the lumbar vertebre, the os sacrum, the ossa innominata, and the false ribs, to which we may add the peritoneum, and a variety of muscles. This cavity encloses the stomach, intestines, omentum or caul, liver, pancreas, spleen, kidneys, urinary bladder, and parts of generation.

Under the division of common integuments are usually included the epidermis, or scarf-skin, the reticulum mucosum of Malpighi, the cutis, or true skin, and the membrana adiposa. The hair and nails, as well as the sebaceous glands, may be considered as appendages to the skin.

SECT. I. Of the Skin.

§ 1. Of the Scarf-Skin.

The epidermis, cuticula, or scarf-skin, is a fine, transparent, and insensible pellicle, destitute of nerves and blood vessels, which invests the body, and everywhere covers the true skin. This scarf-skin, which seems to be very simple, appears, when examined with a microscope, to be composed of several laminae or scales which are increased by pressure, as we may observe in the hands and feet, where it is frequently much thickened, and becomes perfectly callous. It seems to adhere to the cutis by a number of very minute filaments, but may easily be separated from it by heat, or by maceration in water. Some anatomical writers have supposed that it

§ 1. Of the Epidermis.

The epidermis is formed by a moisture exhaled from the whole surface of the body, which gradually hardens when it comes into contact with the air. They were perhaps induced to adopt this opinion, by observing the speedy regeneration of this part of the body when it has been by any means destroyed, it appearing to be renewed on all parts of the surface at the same time; whereas other parts which have been injured, are found to direct their growth from their circumference only towards their centre. But a demonstrative proof that the epidermis is not a fluid hardened by means of the external air, is, that the fetus in utero is found to have this covering. Leeuwenhoek supposed its formation to be owing to the expansion of the extremities of the excretory vessels, which are found everywhere upon the surface of the true skin. Ruysch attributed its origin to the nervous papillae of the skin; and Heister thinks it probable, that it may be owing both to the papillae and the excretory vessels. The celebrated Morgagni, on the other hand, contends*, that it is nothing more than the surface of the cutis, hardened and rendered insensible by the liquor amnii in utero and by the pressure of the air. This is a subject, however, on which we can advance nothing with certainty.

The cuticle is pierced with an infinite number of pores, or little holes, which afford a passage to the hairs, sweat, and insensible perspiration; and likewise to warm water, mercury, and whatever else is capable of being taken in by the absorbents of the skin. The lines which we observe on the epidermis belong to the true skin. The cuticle adjusts itself to them, but does not form them.

§ 2. Of the Rete Mucosum.

Between the epidermis and cutis we meet with an appearance to which Malpighi, who first described it, gave the name of rete mucosum, supposing it to be of a membranous structure, and pierced with an infinite number of pores; but the fact is, that it seems to be nothing more than a mucous substance which may be dissolved by macerating it in water, while the cuticle and cutis preserve their texture.

The colour of the body is found to depend on the colour of this rete mucosum; for in negroes it is observed to be perfectly black, whilst the true skin is of the ordinary colour.

The blisters which raise the skin when burnt or scalded, have been supposed by some to be owing to a rarefaction of this mucus; but they are more probably occasioned by an increased action of the vessels of the part, together with an afflux and effusion of the thinner parts of the blood.

§ 3. Of the Cutis, or True Skin.

The cutis is composed of fibres closely compacted together, as we may observe in leather which is the prepared skin of animals. These fibres form a thick network, which everywhere admits the filaments of nerves, and an infinite number of blood-vessels and lymphatics.

The cutis, when the epidermis is taken off, is found to have, throughout its whole surface, innumerable papillae, which appear like very minute granulations, and seem to be calculated to receive the impressions of the touch, being the most easily observed where the sense of feeling is the most delicate, as in the palms of the hands and on the fingers.

These papillae are supposed by many anatomical writers to be continuations of the pulpy substance of nerves, whose coats have terminated in the cellular texture of the skin. The great sensibility of these papillae evidently proves them to be exceedingly nervous; but surely the nervous fibrillae of the skin are of themselves scarcely equal to the formation of the papillae, and it seems to be more probable that they are formed like the rest of the cutis.

These papillae being described, the uses of the epidermis and the reticulum mucosum will be more easily understood; the latter serving to keep them constantly moist; while the former protects them from the external air, and modifies their too great sensibility.

§ 4. Of the Glands of the Skin.

In different parts of the body we meet, within the substance of the skin, with certain glands or follicles, which discharge a fat and oily humour that serves to lubricate and soften the skin. When the fluid they secrete has acquired a certain degree of thickness, it approaches to the colour and consistence of suet; and from this appearance they have derived their name of sebaceous glands. They are found in the greatest number in the nose, ear, nipple, axilla, groin, scrotum, vagina, and prepuce.

Besides these sebaceous glands, we read, in anatomical books, of others that are described as small spherical bodies placed in all parts of the skin, in much greater abundance than those just now mentioned, and named milia, from their supposed resemblance to millet seed. Steno, who first described these glands, and Malpighi, Ruysch, Verheyen, Winslow, and others, who have adopted his opinions on this subject, speak of them as having excretory ducts, that open on the surface of the cuticle, and distil the sweat and matter of insensible perspiration: and yet, notwithstanding the positive manner in which these pretended glands have been spoken of, we are now sufficiently convinced that their existence is altogether imaginary.

§ 5. Of the Insensible Perspiration and Sweat.

The matter of insensible perspiration, or in other words, the subtle vapour that is continually exhaling from the surface of the body, is not secreted by any particular glands, but seems to be derived wholly from the extremities of the minute arteries that are everywhere dispersed through the skin. These exhaling vessels are easily demonstrated in the dead subject, by throwing water into the arteries; for then small drops exude from all parts of the skin, and raise up the cuticle, the pores of which are closed by death: and in the living subject, a looking-glass placed against the skin, is soon obscured by the vapour. Bidloo fancied he had discovered ducts leading from the cutis to the cuticle, and transmitting this fluid; but in this he was mistaken.

When the perspiration is by any means increased, and several drops that were insensible when separate, are united together and condensed by the external air, they form upon the skin small but visible drops called sweat. This particularly happens after much exercise, or whatever occasions an increased determination of fluids to the surface of the body; a greater quantity of perspirable matter being in such cases carried through the passages that are destined to convey it off.

It has been disputed, indeed, whether the insensible perspiration and sweat are to be considered as one and the same excretion, differing only in degree; or whether they are two distinct excretions derived from different sources. In support of the latter opinion, it has been alleged, that the insensible perspiration is agreeable to nature, and essential to health, whereas sweat may be considered as a species of disease. But this argument proves nothing; and it seems probable, that both the insensible vapour and the sweat are exhaled in a similar manner, though they differ in quantity, and probably in their qualities; the former being more limpid, and seemingly less impregnated with salts than the latter; at any rate we may consider the skin as an emunctory through which the redundant water, and sometimes the other more saline parts of the blood, are carried off. But the insensible perspiration is not confined to the skin only—a great part of what we are constantly throwing off in this way is from the lungs. The quantity of fluid exhaled from the human body by this insensible perspiration is very considerable. Sancutorius (o), an Italian physician, who indefatigably passed a great many years in a series of statical experiments, demonstrated long ago, what has been confirmed by later observations, that the quantity of vapour exhaled from the skin and from the surface of the lungs, amounts nearly to 5-8ths of the aliment we take in. So that if in the warm climate of Italy a person eats and drinks the quantity of eight pounds in the course of a day, five pounds of it will pass off by insensible perspiration, while three pounds only will be evacuated by stool, urine, saliva, &c. But in countries where the degree of cold is greater than in Italy, the quantity of perspired matter is less; in some of the more northern climates, it being found not to equal the discharge by urine. It is likewise observed to vary according to the season of the year, and according to the constitution, age, sex, diseases, diet, exercise, passions, &c. of different people.

From what has been said on this subject, it will be easily conceived, that this evacuation cannot be either much increased or diminished in quantity without affecting the health.

The perspirable matter and the sweat are in some measure analogous to the urine, as appears from their taste and saline nature (r). And it is worthy of observation, that when either of these secretions is increased in quantity, the other is diminished; so that they who perspire the least, usually pass the greatest quantity of urine, and vice versa.

§ 6. Of the Nails.

The nails are of a compact texture, hard and transparent like horn. Their origin is still a subject of dispute. Malpighi supposed them to be formed by a continuation of the papillae of the skin: Ludwig, on the other hand, maintained, that they were composed of the extremities of blood-vessels and nerves. Both these opinions are now deservedly rejected.

They seem to possess many properties in common with the cuticle; like it they are neither vascular nor sensible, and when the cuticle is separated from the true skin by maceration or other means, the nails come away with it.

They appear to be composed of different layers, of unequal size, applied one over the other. Each layer seems to be formed of longitudinal fibres.

In each nail we may distinguish three parts, viz. the root, the body or middle, and the extremity. The root is a soft, thin, and white substance, terminating in the form of a crescent; the epidermis adheres very strongly to this part; the body of the nail is broader, redder, and thicker, and the extremity is of still greater firmness.

The nails increase from their roots, and not from their upper extremity.

Their principal use is to cover and defend the ends of the fingers and toes from external injury.

§ 7. Of the Hair.

The hairs, which from their being generally known, do not seem to require any definition, arise from distinct capsules or bulbs seated in the cellular membrane under the skin (q). Some of these bulbs enclose several

(n) Leeuwenhoek asserts, that one drop of sweat is formed by the conflux of 15 drops of perspirable vapour.

(o) The insensible perspiration is sometimes distinguished by the name of this physician, who was born in the territories of Venice, and was afterwards a professor in the university of Padua. After estimating the aliment he took in, and the sensible secretions and discharges, he was enabled to ascertain with great accuracy the weight or quantity of insensible perspiration by means of a statical chair which he contrived for this purpose; and from his experiments, which were conducted with great industry and patience, he was led to determine what kind of solid or liquid aliment increased or diminished it. From these experiments he formed a system, which he published at Venice in 1614, in the form of aphorisms, under the title of Ars de Medicina Statica.

(p) Minute crystals have been observed to shoot upon the clothes of men who work in glass-houses. Haller. Elem. Phys.

(q) Malpighi, and after him the celebrated Ruysch, supposed the hairs to be continuations of nerves, being of opinion that they originated from the papillae of the skin, which they considered as nervous; and as a corroborating proof of what they advanced, they argued the pain we feel in plucking them out: but later anatomists seem to have rejected this doctrine, and consider the hairs as particular bodies, not arising from the papillae (for in the parts where the papillae abound most there are no hairs), but from bulbs or capsules, which are peculiar to them.

The chief uses of the fat seem to be to afford moisture to all the parts with which it is connected; to facilitate the action of the muscles; and to add to the beauty of the body, by making it everywhere smooth and equal.

Sect. II. Of the Muscles.

The muscles are the organs of motion. The parts that are usually included under this name consist of distinct portions of flesh, susceptible of contraction and relaxation; the motions of which, in a natural and healthy state, are subject to the will, and for this reason they are called voluntary muscles. But besides these, there are other parts of the body that owe their power of contraction to their muscular fibres; thus the heart is of a muscular texture, forming what is called a hollow muscle; and the urinary bladder, stomach, intestines, &c. are enabled to act upon their contents, merely because they are provided with muscular fibres. These are called involuntary muscles, because their motions are not dependent on the will. The muscles of respiration being in some measure influenced by the will, are said to have a mixed motion.

The names by which the voluntary muscles are distinguished, are founded on their size, figure, situation, use, or the arrangement of their fibres, or their origin and insertion. But besides these particular distinctions, there are certain general ones that require to be noticed. Thus, if the fibres of a muscle are placed parallel to each other in a straight direction, they form what is styled a rectilinear muscle; if the fibres cross and intersect each other, they constitute a compound muscle; a radiated one, if the fibres are disposed in the manner of rays; or a penniform muscle, if, like the plume of a pen, they are placed obliquely with respect to the tendon.

Muscles that act in opposition to each other, are called antagonists; thus every extensor muscle has a flexor for its antagonist, and vice versa. Muscles that concur in the same action are styled congeners.

The muscles being attached to the bones, the latter may be considered as levers that are moved in different directions by the contraction of those organs.

That end of a muscle which adheres to the most fixed part is usually called the origin, and that which adheres to the more moveable part, the insertion of the muscle.

In every muscle we may distinguish two kinds of fibres; the one soft, of a red colour, sensible, and irritable, called fleshy fibres; the other of a firmer texture, of a white glistening colour, insensible, without irritability or the power of contracting, and named tendinous fibres. They are occasionally intermixed, but the fleshy fibres generally prevail in the belly or middle part of a muscle, and the tendinous ones in the extremities. If these tendinous fibres are formed into a round

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§ 8. Of the Cellular Membrane and Fat.

The cellular membrane is found to invest the most minute fibres we are able to trace; so that, by modern physiologists, it is very properly considered as the universal connecting medium of every part of the body.

It is composed of an infinite number of minute cells united together, and communicating with each other. The two diseases peculiar to this membrane are proofs of such a communication; for in the emphysema all its cells are filled with air, and in the anaereca they are universally distended with water. Besides these proofs of communication from disease, a familiar instance of it may be observed amongst butchers, who usually puncture this membrane, and by inflating it with air add to the good appearance of their meat.

The cells of this membrane serve as reservoirs to the oily part of the blood, or Fat, which seems to be deposited in them, either by transudation through the coats of the arteries that ramify through these cells, or by particular vessels, continued from the ends of arteries. These cells are not of a glandular structure, as Malpighi and others after him have supposed. The fat is absorbed and carried back into the system by the lymphatics. The great waste of it in many diseases, particularly in the consumption, is a sufficient proof that such an absorption takes place.

The fulness and size of the body are in a great measure proportioned to the quantity of fat contained in the cells of this membrane.

In the living body it seems to be a fluid oil, which concrettes after death. In graminivorous animals, it is found to be of a firmer consistence than in man.

The fat is not confined to the skin alone, being met with everywhere in the interstices of muscles, in the omentum, about the kidneys, at the basis of the heart, in the orbits, &c.

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(r) The hairs likewise differ from each other, and may not be improperly divided into two classes; one of which may include the hair of the head, chin, pubes, and axilla; and the other, the softer hairs, which are to be observed almost everywhere on the surface of the body. round slender cord, they form what is called the tendon of the muscle; on the other hand, if they are spread into a broad flat surface, the extremity of the muscle is styled aponeurosis.

The tendons of many muscles, especially when they are long and exposed to pressure or friction in the grooves formed for them in the bones, are surrounded by a tendinous sheath or fascia, in which we sometimes find a small mucous sac or bursa mucosa, which obviates any inconvenience from friction. Sometimes we find whole muscles, and even several muscles, covered by a fascia of the same kind, that affords origin to many of their fibres, dipping down between them, adhering to the ridges of bones, and thus preventing them from swelling too much when in action. The most remarkable instance of such a covering is the fascia lata of the thigh.

Each muscle is enclosed by a thin covering of cellular membrane, which has been sometimes improperly considered as peculiar to the muscles, and described under the name of propria membrana musculosa. This cellular covering dips down into the substance of the muscle, connecting and surrounding the most minute fibres we are able to demonstrate, and affording a support to their vessels and nerves.

Leeuwenhoek fancied he had discovered, by means of his microscope, the ultimate division of a muscle, and that he could point out the simple fibre, which appeared to him to be a hundred times less than a hair; but he was afterwards convinced how much he was mistaken on this subject, and candidly acknowledged, that what he had taken for a simple fibre was in fact a bundle of fibres.

It is easy to observe several of these fascicula or bundles in a piece of beef, in which, from the coarseness of its texture, they are very evident.

The red colour which particularly distinguishes the muscular or fleshy parts of animals, is owing to an infinite number of blood-vessels, that are dispersed through their substance. When we macerate the fibres of a muscle in water, it becomes of a white colour like all other parts of the body divested of their blood. The blood-vessels are accompanied by nerves, and they are both distributed in such abundance to these parts, that in endeavouring to trace the course of the blood-vessels in a muscle, it would appear to be formed altogether by their ramifications; and in an attempt to follow the branches of its nerves, they would be found to be equal in proportion.

If a muscle is pricked or irritated, it immediately contracts. This is called its irritable principle; and this irritability is to be considered as the characteristic of muscular fibres; and may serve to prove their existence in parts that are too minute to be examined by the eye. This power, which disposes the muscles to contract when stimulated, independent of the will, is supposed to be inherent in them; and is therefore named vis insita. This property is not to be confounded with elasticity, which the membranes and other parts of the body possess in a greater or less degree in common with the muscles; nor with sensibility, for the heart, though the most irritable, seems to be the least sensible of any of the muscular parts of the body.

After a muscular fibre has contracted, it soon returns to a state of relaxation, till it is excited afresh, and then it contracts and relaxes again. We may likewise produce such a contraction, by irritating the nerve leading to a muscle, although the muscle itself is not affected.

This principle is found to be greater in small than in large, and in young than in old, animals.

In the voluntary muscles these effects of contraction and relaxation of the fleshy fibres are produced in obedience to the will, by what may be called the vis nervosa, a property that is not to be confounded with the vis insita. As the existence of a vis insita different from a vis nervosa, was the doctrine taught by Dr Haller in his Elem. Phys., but is at present called in question by several, particularly Dr Monro, we think it necessary to give a few objections, as stated in his Observations on the Nervous System.

"The chief experiment (says the Doctor) which seems to have led Dr Haller to this opinion, is the well-known one, that the heart and other muscles, after being detached from the brain, continue to act spontaneously, or by stimuli may be roused into action, for a considerable length of time; and when it cannot be alleged, says Dr Haller, that the nervous fluid is by the mind, or otherwise, impelled into the muscle.

"That in this instance, we cannot comprehend by what power the nervous fluid or energy can be put in motion, must perhaps be granted: But has Dr Haller given a better explanation of the manner in which his supposed vis insita becomes active?

"If it be as difficult to point out the cause of the action of the vis insita as that of the action of the vis nervosa, the admission of that new power, instead of relieving, would add to our perplexity.

"We should then have admitted, that two causes of a different nature were capable of producing exactly the same effect; which is not in general agreeable to the laws of nature.

"We should find other consequences arise from such a hypothesis, which tend to weaken the credibility of it. For instance, if in a sound animal the vis nervosa alone produces the contraction of the muscles, we will ask what purpose the vis insita serves? If both operate, are we to suppose that the vis nervosa, impelled by the mind or living principle, gives the order, which the vis insita executes, and that the nerves are the intermediaries; and so admit two wise agents employed in every the most simple action? But instead of speculating further, let us learn the effect of experiments, and endeavour from these to draw plain conclusions.

"1. When I poured a solution of opium in water under the skin of the leg of a frog, the muscles, to the surface of which it was applied, were very soon deprived of the power of contraction. In like manner, when I poured this solution into the cavity of the heart, by opening the vena cava, the heart was almost instantly deprived of its power of motion, whether the experiment was performed on it fixed in its place, or cut out of the body.

"2. I opened the thorax of a living frog; and then tied or cut its aorta, so as to put a stop to the circulation of its blood." "I then opened the vena cava, and poured the solution of opium into the heart; and found, not only that this organ was instantly deprived of its powers of action, but that in a few minutes the most distant muscles of the limbs were extremely weakened. Yet this weakness was not owing to the want of circulation, for the frog could jump about for more than an hour after the heart was cut out.

"In the first of these two experiments, we observe the supposed vis insita destroyed by the opium; in the latter the vis nervosa: for it is evident that the limbs were affected by the sympathy of the brain, and of the nervous system in general, with the nerves of the heart.

"3. When the nerve of any muscle is first divided by a transverse section, and then burnt with a hot iron, or punctured with a needle, the muscle in which it terminates contracts violently, exactly in the same manner as when the irritation is applied to the fibres of the muscle. But when the hot iron or needle is confined to the nerve, Dr Haller himself must have admitted, that the vis nervosa, and not the vis insita, was excited. But here I would ask two questions.

"First, Whether we do not as well understand how the vis nervosa is excited when irritation is applied to the muscle as when it is applied to the trunk of the nerve, the impelling power of the mind seeming to be equally wanting in both cases?

"Secondly, If it appears that irritation applied to the trunk of a nerve excites the vis nervosa, why should we doubt that it can equally well excite it when applied to the small and very sensible branches and terminations of the nerve in the muscle?

"As therefore, it appears that the supposed vis insita is destroyed or excited by the same means as the vis nervosa; nay, that when, by the application of opium to the heart of a frog, after the aorta is cut and the circulation interrupted, we have destroyed the vis insita, the vis nervosa is so much extinguished, that the animal cannot act with the distant muscles of the limb; and that these afterwards grow very torpid, or lose much of their supposed vis insita; it seems clearly to follow, that there is no just ground for supposing that any other principle produces the contraction of a muscle."

The vis nervosa, or operation of the mind, if we may so call it, by which a muscle is brought into contraction, is not inherent in the muscle like the vis insita, neither is it perpetual, like this latter property. After long continued or violent exercise, for example, the voluntary muscles become painful, and at length incapable of further action; whereas the heart and other involuntary muscles, the motions of which depend solely on the vis insita, continue through life in a constant state of action, without any inconvenience or waste of this inherent principle.

The action of the vis nervosa on the voluntary muscles constitutes what is called muscular motion; a subject that has given rise to a variety of hypotheses, many of them ingenious, but none of them satisfactory.

Borelli and some others have undertaken to explain the cause of contraction, by supposing that every muscular fibre forms as it were a chain of very minute bladders, while the nerves which are distributed through the muscle, bring with them a supply of animal spirits, which at our will fill these bladders, and by increasing their diameter in width, shorten them, and of course the whole fibre.

Borelli supposes the bladders to be of a rhomboidal shape; Bernouilli, on the other hand, contends that they are oval. Our countryman, Cowper, fancied he had filled them with mercury; the cause of this mistake was probably owing to the mercury's insinuating itself into some of the lymphatic vessels. The late ingenious Mr Elliot undertook to account for the phenomena of muscular motion on principles very different from those just now mentioned. He supposed that a deplogisticated state of the blood is requisite for muscular action, and that a communication of phlogiston to the blood is a necessary effect of such action.

We know that the muscular fibre is shortened, and that the muscle itself swells when in action; but how these phenomena are produced, we are unable to determine. We likewise know that the nerves are essential to muscular motion; for upon dividing or making a ligature round the nerve leading to a muscle, the latter becomes incapable of motion. A ligature made on the artery of a muscle produces a similar effect: a proof this, that a regular supply of blood is also equally necessary to muscular motion. The cause of palsy is usually not to be sought for in the muscle affected, but in the nerve leading to that muscle, or that part of the brain or spinal marrow from which the nerve derives its origin.

Of the particular Muscles.

As the enumeration and description of the particular muscles must be dry and unentertaining to the generality of readers, yet cannot be altogether omitted in a work of this nature, it appeared eligible to throw this part of the subject into the form of a table; in which the name, origin, insertion, and principal use of each muscle will be found described in few words, and occasionally its etymology, when it is of Greek derivation or difficult to be understood.

A TABLE A TABLE of the MUSCLES, arranged according to their SITUATION.

| Muscles situated under the integuments of the cranium, | Name | Origin | Insertion | Use | |------------------------------------------------------|-----------------------|---------------------------------------------|------------------------------------------------|---------------------------------------------------------------------| | | 1. Occipito-frontalis | From the transverse ridge of the os occipitis | Into the skin of the eyebrows. | To pull the skin of the head backwards, and to raise the eyebrows and skin of the forehead. | | | 2. Corrugator supercilii | From above the jointing of the os frontis, os nasi, and os maxillare. | Into the inner part of the occipito-frontalis. | To draw the eyebrows towards each other, and to wrinkle the forehead. | | Of the eyelids, | 1. Orbicularis palpebrarum | From around the edge of the orbit. | Into the nasal process of the os maxillare. | To shut the eye. | | | 2. Levator palpebrae superioris | From the bottom of the orbit, near the optic foramen. | Into the cartilage of the upper eyelid. | To open the eye. | | Of the external ear, | 1. Attollens auriculam | From the tendon of the occipito-frontalis near the os temporis. | Into the upper part of the ear. | To raise the ear. | | | 2. Anterior auriculae | From near the back part of the zygoma. | Into an eminence behind the helix. | To raise this eminence, and to pull it forwards. | | | 3. Retrahentes(s) auriculae | From the outer and back part of the root of the mastoid process. | Into the convex part of the concha. | To stretch the concha, and pull the ear backwards. | | Of the cartilages of the ear, | 1. Tragicus. | From the outer and middle part of the concha, near the tragus. | Into the upper part of the tragus. | To depress the concha, and pull the point of the tragus a little outwards. | | | 2. Anti-tragicus. | From the root of the inner part of the helix. | Into the upper part of the anti-tragus. | To dilate the mouth of the concha. | | | 3. Transversus auriculae | From the upper part of the concha. | Into the inner part of the helix. | To stretch the concha and scapha, and likewise to pull the parts it is connected with towards each other. | | | 4. Helicis major. | From the upper, anterior, and acute part of the helix. | Into the cartilage of the helix, a little above the tragus. | To depress the upper part of the helix. | | | 5. Helicis minor. | From the lower and fore part of the helix. | Into the helix, near the fissure in its cartilage. | To contract the fissure. |

(s) These are three small slender muscles. The inferior one is sometimes wanting. ### Muscles of the Nose

| Name | Origin | Insertion | Use | |-----------------------|------------------------------------------------------------------------|---------------------------------------------------------------------------|----------------------------------------------------------------------| | 1. Compressor naris | From the outer part of the root of the os maxillare, and anterior extremity of the os nasi. | Into the nasal process of the os maxillare, and anterior extremity of the os nasi. | To straighten the nostrils, and likewise to corrugate the skin of the nose. | | 2. Levator labii superioris, alaeque nasi | From the outer part of the orbital process of the os maxillare, and from the nasal process of that bone, where it joins the os frontis. | Into the upper lip and alae of the nose. | To draw the upper lip and skin of the nose upwards and outwards. | | 3. Levator angulioris | From the os maxillare superius, between the orbital foramen and the first dens molaris. | Into the orbicularis oris at the angle of the mouth. | To raise the corner of the mouth. | | 4. Zygomaticus major | From the os maxillare near the zygomatic suture. | Into the angle of the mouth. | To raise the angle of the mouth, and make the cheek prominent as in laughing. | | 5. Zygomaticus minor | Immediately above the origin of the zygomaticus major. | Into the angle of the mouth. | To raise the angle of the mouth obliquely outwards. | | 6. Buccinator | From the alveoli of the dentes molares in the upper and lower jaws. | Into the angle of the mouth. | To contract the mouth and draw the angle of it outwards and backwards. | | 7. Depressor labii inferioris | From the os maxillare superior, immediately above the gums of the dentes incisores. | Into the root of the alae nasi and upper lip. | To draw the alae nasi and upper lip downwards. | | 8. Depressor labii inferioris | At the side of the chin from the lower edge of the maxilla inferior. | Into the angle of the mouth. | To draw the corner of the mouth downwards. | | 9. Levator labii inferioris | From the lower and anterior part of the maxilla inferior. | Into the under lip. | To draw the under lip downwards and somewhat outwards. | | 10. Orbicularis oris (v) | From near the gums of the incisores and caninus of the maxilla inferior. | Into the under lip and skin of the chin. | To raise the under lip and skin of the chin. | | 11. Temporalis | From part of the os bregmatis and os frontis; squamous part of the os temporis; back part of the os maxillare, and the temporal process of the os sphenoideus (v). | Into the coronoid process of the lower jaw. | To shut the mouth by constringing the lips. |

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(t) The nose is affected by fibres of the occipito-frontalis, and by several muscles of the face; but this pair, the compressores, is the only one that is proper to it.

(u) This muscle is in a great measure, if not wholly, formed by the buccinator, zygomatici, depressores, and other muscles that move the lips. Its fibres surround the mouth like a ring.

(v) Some of its fibres likewise have their origin from a strong fascia that covers the muscle and adheres to the bone. ### ANATOMY

| Name | Origin | Insertion | Use | |-----------------------|----------------------------------------------------------------------|--------------------------------------------------------------------------|---------------------------------------------------------------------| | 2. Masseter (w) | From the malar process of the os maxillare, and the lower edges of the os maxillare, and of the zygomatic process of the os temporis. | Into the basis of the coronoid process, and that part of the jaw which supports that and the condyloid process. | To raise and likewise to move the jaw a little forwards and backwards. | | 3. Pterygoideus internus | From the inner surface of the outer wing of the pterygoid process of the os sphenoides, and from the process of the os palati that helps to form the pterygoid fossa. | Into the lower jaw on its inner side and near its angle. | To raise the lower jaw, and draw it a little to one side. | | 4. Pterygoideus externus | From the external ala of the pterygoid process, a small part of the adjacent os maxillare, and a ridge in the temporal process of the os sphenoides. | Into the fore part of the condyloid process of the lower jaw, and likewise of the capsular ligament. | To move the jaw forwards and to the opposite side (x); and at the same time to prevent the ligament of the joint from being pinched. |

**Muscles situated at the fore part of the neck**

1. Latissimus colli (y). From the cellular membrane covering the pectoral, deltoid, and trapezius muscles.

2. Mastoideus (z). From the upper part of the sternum, and from the upper and fore part of the clavicle.

### Situated between the trunk and the os hyoides

1. Omo-hyoideus (A). From the upper costa of the scapula near its niche; from part of a ligament that extends across this niche, and sometimes by a few fibres, from the coracoid process.

Into the basis of the os hyoides.

To draw the os hyoides in an oblique direction downwards.

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*Bone round the whole circumference of its origin. When we remove this covering, we find the muscle of a semicircular shape with its radiated fibres, converging and forming a strong middle tendon.*

(w) So called from its use in chewing, its derivation being from *μανδύω*, *manduco*, "to eat."

(x) This happens when the muscle acts singly. When both act, the jaw is brought horizontally forwards.

(y) This broad and thin muscular expansion, which is situated immediately under the common integuments, is by Winslow named *musculus cutaneous*. Galen gave it the name of *πλατύσμα μυός* (*Platysma myoides*); the etymology of which is from *πλατύς*, *dilatatio*, and *μυός*, *musculus*, and *μοίρα*, *forma*.

(z) This, on account of its two origins, is by Albinus described as two distinct muscles, which he names *sterno-mastoideus* and *cleido mastoideus*.

(A) As this muscle does not always arise from the coracoid process, it seems to have been improperly named *coraco-* ### ANATOMY

| Name | Origin | Insertion | Use | |-----------------------|------------------------------------------------------------------------|---------------------------------------------------------------------------|---------------------------------------------------------------------| | 2. Sterno-hyoideus | From the cartilage of the first rib, the inner and upper part of the sternum, and a small part of the clavicle. | Into the basis of the os hyoideus. | To draw the os hyoideus downwards. | | 3. Hyo-thyroideus | From part of the basis and horn of the os hyoideus. | Into a rough oblique line at the side of the thyroid cartilage. | To raise the thyroid cartilage, or depress the os hyoideus. | | 4. Sterno-thyroideus | From between the cartilages of the 1st and 2d ribs, at the upper and inner part of the sternum. | Immediately under the hyo-thyroideus. | To pull the thyroid cartilage downwards. | | 5. Crico-thyroideus | From the anterior part and side of the cricoid cartilage. | Into the lower part and inferior horn of the thyroid cartilage. | To pull the cricoid cartilage upwards and backwards, or the thyroid forwards and downwards. |

**Muscles situated between the os hyoideus and lower jaw**

1. **Digastricus (B).** - From a fossa at the root of the mastoid process, and likewise from the os hyoideus. - Into the lower and anterior part of the chin. - To draw the lower jaw downwards.

2. **Stylo-hyoideus (C).** - From the basis of the styloid process. - Into the side and fore part of the os hyoideus near its base. - To draw the os hyoideus obliquely upwards.

3. **Mylo-hyoideus (D).** - From the inside of the lower jaw, between the last dens molaris and the chin. - Into the basis of the os hyoideus. - To move the os hyoideus forwards or upwards.

4. **Genio-hyoideus (E).** - From the inside of the chin. - Into the base of the os hyoideus. - To move the os hyoideus forwards or upwards.

5. **Genio-glossus.** - From the inside of the chin. - Into the tongue and basis of the os hyoideus. - To move the tongue in various directions.

6. **Hyo-glossus (F).** - From the horn, basis, and appendix of the os hyoideus. - Into the tongue lately. - To draw the tongue downwards and inwards.

7. **Lingualis.** - Laterally from the root of the tongue. - Into the extremity of the tongue. - To shorten the tongue and draw it backwards.

8. **Stylo-glossus.**

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*Coraco-hyoideus* by Douglas and Albinus. Winslow calls it *omo-hyoideus*, on account of its general origin from the scapula.

(b) from *biventer* (biventer), because it has two fleshy bellies with a middle tendon. This tendon passes through the stylo-hyoideus.

(c) In some subjects we meet with another muscle, which, from its having nearly the same origin, insertion, and use as this, has been named *stylo-hyoideus alter*.

(d) So named from its arising near the dentes molares (*mola*) and its being inserted into the os hyoideus.

(e) From *mentum*, "the chin."

(f) From *lingua*, "tongue." ### ANATOMY

| Name | Origin | Insertion | Use | |-----------------------|----------------------------------------------------------------------|--------------------------------------------------------------------------|---------------------------------------------------------------------| | 8. Stylo-glossus | From the styloid process, and sometimes also from a ligament that extends from thence to the angle of the lower jaw. | Into the side of the tongue from the root to near its tip. | To move the tongue backwards and to one side. | | 9. Stylo-pharyngeus | From the basis of the styloid process. | Into the side of the pharynx and posterior part of the thyroid cartilage.| To raise the thyroid cartilage and pharynx, and likewise to dilate the latter. | | 10. Circumflexus palati | From near the bony part of the Eustachian tube, and from the spinous process of the os sphenoides. | Into the semilunar edge of the os palati and the velum pendulum palati (c). | To dilate and draw the velum obliquely downwards. | | 11. Levator palati | From the membranous part of the Eustachian tube, and the extremity of the os petrosum. | Into the velum pendulum palati. | To pull the velum backwards. |

**Muscles situated about the fauces,**

1. Palato-pharyngeus. From the lower and anterior part of the cartilaginous extremity of the Eustachian tube (H); the tendinous expansion of the circumflexus palati; and the velum pendulum palati near the basis and back part of the uvula.

Into the upper and posterior part of the thyroid cartilage. To raise the pharynx and thyroid cartilage, or to pull the velum and uvula backwards and downwards.

2. Constrictor isthmi faucium. From near the basis of the tongue laterally. Into the velum pendulum palati, near the basis and fore part of the uvula. To raise the tongue and draw the velum towards it (i).

3. Azygos uvulae. From the end of the suture that unites the ossa palati. Into the extremity of the uvula. To shorten the uvula, and bring it forwards and upwards.

---

**at the back part of the pharynx,**

1. Constrictor pharyngis superior. From the cuneiform process of the occipital bone; the pterygoid process of the os sphenoides; and from each jaw near the last dens molaris (K).

Into the middle of the pharynx. To move the pharynx upwards and forwards, and to compress its upper part.

---

(g) This muscle in its course forms a round tendon, which, after passing over a kind of hook formed by the inner plate of the pterygoid process of the sphenoid bone, expands into a tendinous membrane.

(h) The few fibres that arise from the Eustachian tube are described as a distinct muscle by Albinus, under the name of salpingo-pharyngeus. They serve to dilate the mouth of the tube.

(i) This muscle, and the palato-pharyngeus, likewise serve to close the passage into the fauces, and to carry the food into the pharynx.

(k) The three orders of fibres here mentioned, with a few others derived from the tongue, have given occasion to Douglas to describe them as four distinct muscles, under the names of cephalo-pharyngeus, mylo-pharyngeus, ptery pharyngeus, and glosso-pharyngeus. ### ANATOMY

#### Muscles about the glottis

| Name | Origin | Insertion | Use | |-------------------------------|---------------------------------------------|------------------------------------------------|-----------------------------------------------| | 1. Crico-arytenoideus lateralis | From the side of the cricoid cartilage | Into the basis of the arytenoid cartilage | To open the glottis. | | 2. Arytenoideus obliquus | From the basis of one of the arytenoid | Near the extremity of the other arytenoid | To draw the parts it is connected with | | | cartilages | cartilage. | towards each other. | | 3. Arytenoideus transversus | From one of the arytenoid cartilages | In the other arytenoid cartilage laterally. | To shut the glottis. | | 4. Thyreo-arytenoideus | From the posterior and under part of the | Into the arytenoid cartilage. | To draw the arytenoid cartilage forwards. | | | thyroid cartilage | | | | 5. Aryteno-epiglotticus | From the upper part of the arytenoid | Into the side of the epiglottis. | To move the epiglottis outwards. | | | cartilage laterally | | | | 6. Thyreo-epiglotticus | From the thyroid cartilage | Into the side of the epiglottis. | To pull the epiglottis obliquely downwards (x).| | | | | |

#### At the fore part of the neck close to the vertebrae

| Name | Origin | Insertion | Use | |-------------------------------|---------------------------------------------|------------------------------------------------|-----------------------------------------------| | 1. Rectus capitis internus major | From the anterior extremities of the | Into the fore part of the cuneiform process | To bend the head forwards. | | | transverse processes of the five lowest | of the os occipitis. | | | | cervical vertebra. | | | | 2. Rectus capitis internus minor | From the anterior and upper part of the | Near the basis of the condyloid process of the | To assist the last described muscle. | | | first cervical vertebra. | os occipitis. | | | 3. Rectus capitis lateralis | From the anterior and upper part of the | Into the os occipitis, opposite to the stylo- | To move the head to one side. | | | transverse process of the first cervical | mastoid foramen. | | | | vertebra. | | | | 4. Longus colli | Within the thorax, laterally from the bodies | Into the second cervical vertebra anteriorly. | To pull the neck to one side (o). | | | of the three uppermost dorsal vertebra; | | | | | from the basis and fore part | | |

---

(1) Douglas makes two muscles of this, the hyo-pharyngeus and syndesmo-pharyngeus.

(2) The crico-pharyngeus and thyro-pharyngeus of Douglas.

(x) When either this or the preceding muscle acts with its fellow, the epiglottis is drawn directly downwards upon the glottis.

(o) When both muscles act, the neck is drawn directly forwards. ### ANATOMY

| Name | Origin | Insertion | Use | |-----------------------|----------------------------------------------------------------------|--------------------------------------------------------------------------|---------------------------------------------------------------------| | | of the transverse processes of the first and second dorsal vertebrae, and of the last cervical vertebra; and lastly, from the anterior extremities of the transverse processes of the 6th, 5th, 4th, and 3rd cervical vertebrae. | Into the linea alba (p), ossa pubis (q), and spine of the ilium (r). | To compress and support the viscera, assist in evacuating the feces and urine, draw down the ribs, and bend the trunk forwards or obliquely to one side. |

**Muscles at the fore part of the abdomen:**

1. **Obliquus externus.** - From the lower edges of the eight inferior ribs near their cartilages. - Into the linea alba (p), ossa pubis (q), and spine of the ilium (r). - To assist the obliquus externus.

2. **Obliquus internus.** - From the spinous process of the three lowermost lumbar vertebrae, the back part of the os sacrum, the spine of the ilium, and back part of Fallopian's ligament (r). - Into the cartilages of all the false ribs, linea alba (s), and fore part of the pubis. - To assist the obliquus externus.

3. **Transversalis.** - From the cartilages of the seven inferior ribs; the transverse processes of the last dorsal, and four upper lumbar vertebrae; the inner part of Fallopian's ligament and the spine of the ilium. - Into the linea alba and cartilago ensiformis. - To compress the abdominal viscera.

4. **Rectus**

---

(p) The linea alba is that tendinous expansion which reaches from the cartilago ensiformis to the os pubis. It is formed by the interlacement of the tendinous fibres of the oblique and transverse muscles, and on this account some anatomists have considered these as three digastric muscles.

(q) A little above the pubis the tendinous fibres of this muscle separate from each other, so as to form an opening called the ring of the obliquus externus, and commonly, though improperly, the ring of the abdominal muscles, there being no such aperture either in the transversalis or obliquus internus. This ring in the male subject affords a passage to the spermatic vessels, and in the female to the round ligament of the uterus.

(r) From the anterior and upper spinous process of the ilium, this muscle is stretched tendinous to the os pubis, and thus forms what is called by some Fallopian's, and by others Ponpart's ligament. The blood-vessels pass under it to the thigh.

(s) The tendon formed by the upper part of the muscle in its way to the linea alba is divided into two layers. The posterior layer runs under, and the anterior one over, the rectus muscle.

(t) From this part it detaches some fibres which extend downwards upon the spermatic chord, and form what is described as the cremaster muscle. ### ANATOMY

| Name | Origin | Insertion | Use | |-----------------------|------------------------------------------------------------------------|---------------------------------------------------------------------------|---------------------------------------------------------------------| | **4. Rectus abdominis** | From the upper edge of the pubis and the symphysis pubis. | Into the cartilages of the 5th, 6th, and 7th ribs, and the edge of the cartilage ensiformis (u). | To compress the fore part of the abdomen, and to bend the trunk forwards. | | **5. Pyramidalis (v)** | From the anterior and upper part of the pubis. | Into the linea alba and inner edge of the rectus, commonly about two inches above the pubis. | To assist the lower portion of the rectus. |

**Muscles at the fore part of the thorax**

1. **Pectoralis major** - From the cartilaginous ends of the 5th and 6th ribs; the sternum, and anterior part of the clavicle. - Into the upper and inner part of the os humeri (w). - To draw the arm forwards, or obliquely forwards.

2. **Subclavius** - From the cartilage of the first rib. - Into the under surface of the clavicle. - To move the clavicle forwards and downwards, and to assist in raising the first rib.

3. **Pectoralis minor (x)** - From the upper edges of the 3rd, 4th, and 5th ribs. - Into the coracoid process of the scapula. - To move the scapula forwards and downwards, or to elevate the ribs.

4. **Serratus magnus** - From the eight superior ribs. - Into the basis of the scapula. - To bring the scapula forwards.

---

**Muscles that concur in forming the thorax**

1. **Diaphragma (y)** - From the transverse processes of the last cervical, and the eleven upper dorsal vertebrae. - Into the upper side of each rib, near its tuberosity. - To move the ribs upwards and outwards.

2. **Levatores costarum** - From the lower edge of each upper rib. - Into the superior edge of each lower rib. - To elevate the ribs.

3. **Intercostales externi** - From the spine to their cartilages; from thence to the sternum, there being only a thin membrane, which is spread over the intercostales interni; and that the latter, on the contrary, extend only from the sternum to the angles of each rib.

4. **Intercostales interni (A)** - To elevate the ribs.

---

(u) The fibres of the rectus are generally divided by three tendinous intersections. The two upper thirds of this muscle passing between the tendinous layers of the obliquis internus, are enclosed as it were in a sheath; but at its lower part we find it immediately contiguous to the peritoneum, the inferior portion of the tendon of the transversalis passing over the rectus, and adhering to the interior layer of the obliquis internus.

(v) This muscle is sometimes wanting.

(w) The fibres of this muscle pass towards the axilla in a folding manner, and with those of the latissimus dorsi form the arm-pit.

(x) This and some other muscles derive their name of serratus, from their arising by a number of tendinous or fleshy digitations, resembling the teeth of a saw (terra).

(y) For a description of the diaphragm, see Chap. IV. Sect. IV.

(A) The origin, insertion, and use of the internal intercostals, are similar to those of the external. The reader, however, will be pleased to observe, that the intercostales externi occupy the spaces between the ribs only from the spine to their cartilages; from thence to the sternum, there being only a thin membrane, which is spread over the intercostales interni; and that the latter, on the contrary, extend only from the sternum to the angles of each rib.

The fibres of the external muscles run obliquely forwards; those of the internal obliquely backwards. This difference in the direction of their fibres induced Galen to suppose that they were intended for different uses; that the external intercostals, for instance, serve to elevate, and the internal ones to depress the ribs. Fallopia seems to have been the first who ventured to dispute the truth of this doctrine, which has since been revived by Boyle. ### Muscles at the back part of the neck and trunk

1. **Trapezius (c), or cucullaris.** - **Origin:** From the middle of the os occipitis, and the spinous processes of the two inferior cervical, and of all the dorsal vertebrae (d). - **Insertion:** Into the posterior half of the clavicle, part of the acromion, and the spine of the scapula. - **Use:** To move the scapula.

2. **Rhomboideus (E).** - **Origin:** From the spinous processes of the three lowermost cervical, and of all the dorsal vertebrae. - **Insertion:** Into the basis of the scapula. - **Use:** To move the scapula upwards and backwards.

3. **Latissimus dorsi.** - **Origin:** From part of the spine of the os ilium, the spinous processes of the os sacrum and lumbar vertebrae; and of six or eight of the dorsal vertebrae; also from the four inferior false ribs near their cartilages. - **Insertion:** Into the os humeri, at the inner edge of the groove for lodging the long head of the biceps muscle. - **Use:** To draw the os humeri downwards and backwards, and to roll it upon its axis.

4. **Serratus inferior posticus.** - **Origin:** From the spinous processes of the two lowermost dorsal, and of three of the lumbar vertebrae. - **Insertion:** Into the lower edges of the three or four lowermost ribs near their cartilages. - **Use:** To draw the ribs outwards, downwards, and backwards.

5. **Levator scapulae.** - **Origin:** From the transverse processes of the four uppermost vertebrae colli. - **Insertion:** Into the upper angle of the scapula. - **Use:** To move the scapula forwards and upwards.

6. **Serratus superior posticus.** - **Origin:** From the lower part of the ligamentum colli, the spinous process of the lowermost cervical vertebrae, and of the two superior dorsal vertebrae. - **Insertion:** Into the 2d, 3d, and 4th ribs. - **Use:** To expand the thorax.

---

Boyle, and more lately still by Hamberger, whose theoretical arguments on this subject have been clearly refuted by the experiments of Haller.

(b) These consist of four, and sometimes five distinct muscles on each side. Vesalius, and after him Douglas and Albinus, consider them as forming a single muscle, which, on account of its shape, they named triangularis. Verheyen, Winslow, and Haller, more properly describe them as so many separate muscles, which, on account of their origin and insertion, they name sterno-costales.

(c) So named by Riolanus, from τραπεζίς, on account of its quadrilateral shape. Columbus and others give it the name of cucullaris, from its resemblance to a monk's hood.

(d) The tendinous fibres of this muscle, united with those of its fellow in the nape of the neck, form what is called the ligamentum colli.

(e) This muscle consists of two distinct portions, which are described as separate muscles by Albinus, under the names of rhomboideus minor and rhomboideus major. ### ANATOMY

#### Of the Muscles

| Name | Origin | Insertion | Use | |-----------------------|------------------------------------------------------------------------|--------------------------------------------------------------------------|---------------------------------------------------------------------| | 7. Splenius (z) | From the spinous processes of the four or five uppermost vertebrae of the back, and of the lowermost cervical vertebra. | Into the transverse processes of the two first cervical vertebrae, the upper and back part of the mastoid process, and a ridge on the os occipitis. | To move the head backwards. | | 8. Complexus (a) | From the transverse processes of the four or five uppermost dorsal, and of the six lowermost cervical vertebrae. | Into the os occipitis. | To draw the head backwards. | | 9. Trachelo-mastoideus (h) | From the transverse processes of the first dorsal vertebra and four or five of the lowermost cervical vertebrae. | Into the mastoid process. | To draw the head backwards. | | 10. Rectus capitis posticus major | From the spinous process of the second cervical vertebra. | Into the os occipitis. | To extend the head and draw it backwards. | | 11. Rectus capitis posticus minor | From the first vertebra of the neck. | Into the os occipitis. | To assist the rectus major. | | 12. Obliquus superior capitis | From the transverse process of the first cervical vertebra. | Into the os occipitis. | To draw the head backwards. | | 13. Obliquus inferior capitis | From the spinous process of the second cervical vertebra. | Into the transverse process of the first cervical vertebra. | To draw the face towards the shoulder, and to move the first vertebra upon the second. | | 14. Sacro-lumbalis (t) | From the back part of the os sacrum, spine of the ilium, spinous processes, and roots of the transverse processes of the vertebrae of the loins. | Into the lower edge of each rib. | To draw the ribs downwards, move the body upon its axis, assist in erecting the trunk, and turn the neck backwards, or to one side. | | 15. Longissimus dorsi (k) | The same as that of the sacro-lumbalis. | Into the transverse processes of the dorsal vertebrae. | To stretch the vertebrae of the back, and keep the trunk erect. |

---

(f) According to some writers, this muscle has gotten its name from its resemblance to the spleen; others derive it from splenium, splint.

(g) So named on account of its complicated structure.

(h) So named from its origin from the neck (τραχεία) and its insertion into the mastoid process.

(i) Several thin fasciculi of fleshy fibres arise from the lower ribs, and terminate in the inner side of this muscle. Steno names them musculi ad sacro-lumbalem accessorii. The sacro-lumbalis likewise sends off a fleshy slip from its upper part, which by Douglas and Albinus is described as a distinct muscle, under the name of cervicolis descendens. Morgagni has very properly considered it as part of the sacro-lumbalis.

(k) At the upper part of this muscle a broad thin layer of fleshy fibres is found crossing, and intimately adhering to it. This portion, which is described by Albinus under the name of transversalis cervicis, may very properly be considered as an appendage to the longissimus dorsi. It arises from the transverse processes of the five or six superior dorsal vertebrae, and is inserted into the transverse processes of the six inferior cervical vertebrae. By means of this appendage the longissimus dorsi may serve to move the neck to one side, or obliquely backwards. ### ANATOMY

| Name | Origin | Insertion | Use | |-----------------------|------------------------------------------------------------------------|---------------------------------------------------------------------------|----------------------------------------------------------------------| | 16. Spinalis dorsi | From the spinous processes of the uppermost lumbar and lowermost dorsal vertebrae. | Into the spinous processes of the nine superior dorsal vertebrae. | To extend the vertebral column. | | 17. Semi-spinalis dor- | From the transverse processes of the 7th, 8th, 9th, and 10th vertebrae of the back. | Into the spinous processes of the four uppermost dorsal, and lowermost of the cervical vertebrae. | To extend the spine obliquely backwards. | | 18. Multifidus spinae (L) | From the os sacrum, ilium, oblique and transverse processes of the lumbar vertebrae, transverse processes of the dorsal and four of the cervical vertebrae. | Into the spinous processes of the lumbar, dorsal, and six of the cervical vertebrae. | To extend the back, and draw it backwards or to one side. | | 19. Semi-spinalis colli | From the transverse processes of the five or six uppermost dorsal vertebrae. | Into the spinous processes of the 2nd, 3rd, 4th, 5th, and 6th cervical vertebrae. | To stretch the neck obliquely backwards. | | 20. Scalenus (M) | From the transverse processes of the five inferior cervical vertebrae. | Into the upper and outer part of the first and second ribs. | To move the neck forwards, or to one side. | | 21. Inter-spinales (N) | From the upper part of each of the spinous processes of the six inferior cervical vertebrae. | Into the under part of each of the spinous processes of the vertebrae above. | To draw the spinous processes towards each other. | | 22. Inter-transversales (O) | From the upper part of each of the transverse processes of the vertebrae. | Into the under part of each of the transverse processes of the vertebrae above. | To draw the transverse processes towards each other. |

**Muscles within the cavity of the abdomen, on the anterior and lateral parts of the spine,**

1. Psoas parvus (P). From the sides and transverse processes of the uppermost lumbar vertebra, and sometimes of the lowermost dorsal vertebra. Into the brim of the pelvis, at the junction of the os pubis with the ilium. To bend the loins forwards.

---

(1) Anatomists in general have unnecessarily multiplied the muscles of the spine. Albinus has the merit of having introduced greater simplicity into this part of myology. Under the name of *multifidus spine*, he has very properly included those portions of muscular flesh intermixed with tendinous fibres, situated close to the back part of the spine, and which are described by Douglas under the names of *transversales colli*, *dorsi*, et *lumborum*.

(m) The ancients gave it this name from its resemblance to an irregular triangle (*εκλάματος*). It consists of three fleshy portions. The anterior one affords a passage to the axillary artery, and between this and the middle portion we find the nerves going to the upper extremities. The middle is in part covered by the posterior portion, which is the longest and thinnest of the three.

(n) In the generality of anatomical books we find these muscles divided into *inter-spinales cervicis*, *dorsi*, and *lumborum*; but we do not find any such muscles either in the loins or back.

(o) These muscles are to be found only in the neck and loins; what have been described as the *inter-transversales dorsi* being rather small tendons than muscles.

(p) This and the following pair of muscles derive their name of *psoas* from *ψῶα*, *lambus*, on account of their situation at the anterior part of the loins. ### Anatomy

#### Muscles

| Name | Origin | Insertion | Use | |-----------------------|----------------------------------------------------------------------|--------------------------------------------------------------------------|---------------------------------------------------------------------| | 2. Psoas magnus | From the bodies and transverse processes of the last dorsal, and all the lumbar vertebrae. | Into the os femoris, a little below the trochanter minor. | To bend the thigh forwards. | | 3. Iliacus internus | From the inner lip, hollow part, and edge of the os ilium. | In common with the psoas magnus. | To assist the psoas magnus. | | 4. Quadratus lumborum (Q) | From the posterior part of the spine of the ilium. | Into the transverse processes of the four uppermost lumbar vertebrae, the inferior edge of the last rib, and the side of the lowermost dorsal vertebra. | To support the spine, or to draw it to one side. | | 5. Coccygeus | From the posterior and inner edge of the spine of the ischium. | Into the lower part of the os sacrum, and almost the whole length of the os coccygis laterally. | To draw the os coccygis forwards and inwards (R). |

#### Muscles on the scapula and upper part of the os humeri:

1. **Deltoides (S)** - From the clavicle, processus acromion, and spine of the scapula. - Into the anterior and middle part of the os humeri. - To raise the arm.

2. **Supra-spinatus** - From the basis, spine, and upper costa of the scapula. - Into a large tuberosity at the head of the os humeri. - To raise the arm.

3. **Infra-spinatus** - From the basis and spine of the scapula. - Into the upper and middle part of the tuberosity. - To roll the os humeri outwards.

4. **Teres minor (T)** - From the inferior costa of the scapula. - Into the lower part of the tuberosity. - To assist the infra-spinatus.

5. **Teres major** - From the inferior angle, and inferior costa of the scapula. - Into the ridge at the inner side of the groove formed for the long head of the biceps. - To assist in the rotary motion of the arm.

6. **Subscapularis** - From the basis, superior and inferior costa of the scapula. - Into the upper part of a small tuberosity at the head of the os humeri. - To roll the arm inwards.

7. **Coraco-brachialis (U)** - From the coracoid process of the scapula. - Into the middle and inner side of the os humeri. - To roll the arm forwards and upwards.

---

(a) So called from its shape, which is that of an irregular square. (b) Some of the fibres of this muscle are united with those of the levator ani, so that it assists in closing the lower part of the pelvis. (c) So named from its supposed resemblance to the Greek Δ reversed. (t) This and the following pair are called teres, from their being of a long and round shape. (u) This muscle affords a passage to the musculo-cutaneous nerve. ### Muscles on the Os Humeri

| Name | Origin | Insertion | Use | |-----------------------|------------------------------------------------------------------------|-----------------------------------------------|------------------------------| | **1. Biceps flexor cubiti** | By two heads, one from the coracoid process, and the other, or long head, from the upper and outer edge of the glenoid cavity of the scapula. | Into the tuberosity at the upper end of the radius. | To bend the fore-arm. | | **2. Brachialis internus** | From the os humeri, below, and at each side of the tendon of the deltoides. | Into a small tuberosity at the fore part of the coronoid process of the ulna. | To assist in bending the fore-arm. | | **3. Tricep extensor cubiti** | By three heads: the first, from the inferior costa of the scapula; the second, from the upper and outer part of the os humeri; and the third, from the back part of that bone. | Into the upper and outer part of the olecranon. | To extend the forearm. |

---

**On the Forearm**

| Name | Origin | Insertion | Use | |-----------------------|------------------------------------------------------------------------|-----------------------------------------------|------------------------------| | **1. Supinator longus** | From the outer ridge and anterior surface of the os humeri, a little above its outer condyle. | Into the radius near its styloid process. | To assist in turning the palm of the hand upwards. | | **2. Extensor carpi radialis longus** | Immediately below the origin of the supinator longus. | Into the upper part of the metacarpal bone of the fore-finger. | To extend the wrist. | | **3. Extensor carpi radialis brevis** | From the outer lower part of the outer condyle of the os humeri, and the upper part of the radius. | Into the upper part of the metacarpal bone of the middle finger. | To assist the extensor longus. | | **4. Extensor digitorum communis** | From the outer condyle of the os humeri. | Into the back part of all the bones of the four fingers. | To extend the fingers. | | **5. Extensor minimi digiti** | From the outer condyle of the os humeri. | Into the bones of the little finger. | To extend the little finger. | | **6. Extensor carpi ulnaris** | From the outer condyle of the os humeri. | Into the metacarpal bone of the little finger. | To assist in extending the wrist. | | **7. Anconeus (v.)** | From the outer condyle of the os humeri. | Into the outer edge of the ulna. | To extend the forearm. | | **8. Flexor carpi ulnaris** | From the inner condyle of the os humeri, and anterior edge of the olecranon (w). | Into the os pisiforme. | To assist in bending the hand. | | **9. Palmaris longus** | From the inner condyle of the os humeri. | Into the internal annular ligament, and aponeurosis palmaris (x). | To bend the arm. |

---

(v) So called from *a* *cubitus*.

(w) Between the two origins of this muscle we find the ulnar nerve going to the fore-arm.

(x) The aponeurosis palmaris is a tendinous membrane that extends over the palm of the hand. Some anatomists ### Anatomy

| Name | Origin | Insertion | Use | |-------------------------------|------------------------------------------------------------------------|--------------------------------------------------------------------------|----------------------------------------------------------------------| | 10. Flexor carpi radialis | From the inner condyle of the os humeri. | Into the metacarpal bone of the forefinger. | To bend the hand. | | 11. Pronator radii teres | From the outer condyle of the os humeri, and coronoid process of the ulna. | Into the anterior and convex edge of the radius, near its middle. | To roll the hand inwards. | | 12. Flexor sublimis perforatus (γ) | From the inner condyle of the os humeri, inner edge of the coronoid process of the ulna, and upper and anterior part of the radius. | Into the second bone of each finger. | To bend the second joint of the fingers. | | 13. Supinator radii brevis | From the outer condyle of the os humeri, and posterior surface and outer edge of the ulna. | Into the anterior, inner, and upper part of the radius. | To roll the radius outwards. | | 14. Abductor pollicis longus | From the middle and back part of the ulna, interosseous ligament, and radius. | By two tendons into the os trapezium, and first bone of the thumb. | To stretch the first bone of the thumb outwards. | | 15. Extensor minor pollicis | From the back part of the ulna, and interosseous ligament and radius. | Into the convex part of the second bone of the thumb. | To extend the second bone of the thumb obliquely outwards. | | 16. Extensor major pollicis | From the back of the ulna and interosseous ligament. | Into the third last bone of the thumb. | To stretch the thumb obliquely backwards. | | 17. Indicator | From the middle of the ulna. | Into the metacarpal bone of the forefinger. | To extend the forefinger. | | 18. Flexor profundus perforans | From the upper and fore part of the ulna, and interosseous ligament. | Into the fore part of the last bone of each of the fingers. | To bend the last joint of the fingers. | | 19. Flexor longus pollicis | From the upper and fore part of the radius. | Into the last joint of the thumb. | To bend the last joint of the thumb. | | 20. Pronator radii quadratus | From the inner and lower part of the ulna. | Into the radius, opposite to its origin. | To roll the radius inwards, and of course to assist in the pronation of the hand. |

**Muscles on the hand**

1. Lumbricales (z). From the tendons of the perforans. Into the tendons of the extensor digitorum communis. To bend the first, and to extend the two last joints of the fingers (λ).

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(γ) This muscle is named perforatus, on account of the four tendons, in which it terminates, being perforated by those of another muscle, the perforans.

(z) So named from their being shaped somewhat like the lumbricus or earth-worm.

(λ) Fallopius was the first who remarked the two opposite uses of this muscle. Their extending power is owing to their connexion with the extensor communis. ### ANATOMY

| Name | Origin | Insertion | Use | |-----------------------|----------------------------------------------------------------------|--------------------------------------------------------------------------|---------------------------------------------------------------------| | 2. Abductor brevis pollicis. | From the fore part of the internal annular ligament, os scaphoides, and one of the tendons of the abductor longus pollicis. | Into the outer side of the second bone of the thumb, near its root. | To move the thumb from the fingers. | | 3. Opponens pollicis. | From the inner and anterior part of the internal annular ligament, and from the os scaphoides. | Into the first bone of the thumb. | To move the thumb inwards, and to turn it upon its axis. | | 4. Flexor brevis pollicis. | From the os trapezoides, internal annular ligament, os magnum, and os unciforme. | Into the ossa sesamoidae and second bone of the thumb. | To bend the second joint of the thumb. | | 5. Adductor pollicis. | From the metacarpal bone of the middle finger. | Into the basis of the second bone of the thumb. | To move the thumb towards the fingers. | | 6. Abductor indicis. | From the inner side of the first bone of the thumb, and from the os trapezium. | Into the first bone of the fore finger posteriorly. | To move the fore finger towards the thumb. | | 7. Palmaris brevis. | From the internal annular ligament, and aponeurosis palmaris. | Into the os pisiforme, and the skin covering the abductor minimi digiti. | To contract the palm of the hand. | | 8. Abductor minimi digiti. | From the internal annular ligament, and os pisiforme. | Into the side of the first bone of the little finger. | To draw the little finger from the rest. | | 9. Flexor parvus minimi digiti. | From the os unciforme and internal annular ligament. | Into the first bone of the little finger. | To bend the little finger. | | 10. Adductor metacarpi minimi digiti. | From the os unciforme and internal annular ligament. | Into the metacarpal bone of the little finger. | To move that bone towards the rest. | | 11. Interossei interni. | Situated between the metacarpal bones. | Into the roots of the fingers. | To extend the fingers, and move them towards the thumb (B). | | 12. Interossei externi. | Situated between the metacarpal bones on the back of the hand. | Into the roots of the fingers. | To extend the fingers; but the first draws the middle finger inwards, the second draws it outwards, and the third draws the ring finger inwards. |

**Muscles at the back part of the pelvis, and upper part of the thigh,**

1. Gluteus (c) maximus.

From the spine of the ilium, posterior sacro-ischiatric ligament, os sacrum, and os coccygis.

Into the upper part of the linea aspera of the os femoris.

To extend the thigh and draw it outwards.

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(B) The third interosseus internus (for there are four of the externi and three of the interni) differs from the rest in drawing the middle finger from the thumb.

(c) From γλαυκος, nates. ### ANATOMY

#### Muscles on the Thigh (g)

| Name | Origin | Insertion | Use | |-----------------------|------------------------------------------------------------------------|---------------------------------------------------------------------------|----------------------------------------------------------------------| | 2. Gluteus medius | From the spine and superior surface of the ilium. | Into the outer and back part of the great trochanter of the os femoris. | To draw the thigh outwards and a little backwards, and when it is bended, to roll it. | | 3. Gluteus minimus | From the outer surface of the ilium and the border of its great niche. | Into the upper and anterior part of the great trochanter. | To assist the former. | | 4. Pyriformis (d) | From the anterior part of the os sacrum. | Into a cavity at the root of the trochanter major. | To roll the thigh outwards. | | 5. Gemini (e) | By two portions, one from the outer surface of the spine of the ischium; the other from the tuberosity of the ischium and posterior sacro-ischiatric ligament. | Into the same cavity as the pyriformis. | To roll the thigh outwards, and likewise to confine the tendon of the obturator internus, when the latter is in action. | | 6. Obturator internus | From the superior half of the inner border of the foramen thyroideum. | Into the same cavity with the former. | To roll the thigh outwards. | | 7. Quadratus (f) femoris | From the tuberosity of the ischium. | Into a ridge between the trochanter major and trochanter minor. | To move the thigh outwards. |

#### Muscles on the Thigh (g)

| Name | Origin | Insertion | Use | |-----------------------|------------------------------------------------------------------------|---------------------------------------------------------------------------|----------------------------------------------------------------------| | 1. Biceps flexor cruris | By two heads; one from the tuberosity of the ischium, the other from the linea aspera near the insertion of the gluteus maximus. | Into the upper and back part of the fibula (h). | To bend the leg. | | 2. Semi-tendinosus | From the tuberosity of the ischium. | Into the upper and back part of the head of the tibia. | To bend the leg. | | 3. Semi-membranosus | From the tuberosity of the ischium. | Into the upper and back part of the head of the tibia. | To bend the leg. | | 4. Tensor vaginæ femoris | From the superior and anterior spinous process of the ilium. | Into the inner side of the fascia lata, which covers the outside of the thigh. | To stretch the fascia lata. |

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(d) So named from its pear-like shape.

(e) The two portions of this muscle having been described as two distinct muscles by some anatomists, have occasioned it to be named *gemini*. The tendon of the obturator internus runs between these two portions.

(f) The muscle is not of the square shape its name would seem to indicate.

(g) The muscles of the leg and thigh are covered by a broad tendinous membrane called *fascia lata*, that surrounds them in the manner of a sheath. It is sent off from the tendons of the glutei and other muscles, and dipping down between the muscles it covers, adheres to the linea aspera, and spreading over the joint of the knee, gradually disappears on the leg. It is thickest on the inside of the thigh.

(h) The tendon of this muscle forms the *outer ham-string*.

(i) So named on account of its origin, which is by a broad flat tendon three inches long. | Name | Origin | Insertion | Use | |-----------------------|------------------------------------------------------------------------|--------------------------------------------------------------------------|---------------------------------------------------------------------| | 5. Sartorius | From the superior and anterior spinous process of the ilium. | Into the upper and inner part of the tibia. | To bend the leg inwards (k). | | 6. Rectus | By two tendons; one from the anterior and inferior spinous process of the ilium; the other from the posterior edge of the cotyloid cavity. | Into the upper and fore part of the patella. | To extend the leg. | | 7. Gracilis | From the fore part of the ischium and pubis. | Into the upper and inner part of the tibia. | To bend the leg. | | 8. Vastus externus (L) | From the anterior and lower part of the great trochanter, and the outer edge of the linea aspera. | To the upper and outer part of the patella. | To extend the leg. | | 9. Vastus internus | From the inner edge of the linea aspera, beginning between the fore part of the os femoris and the root of the lesser trochanter. | Into the upper and inner part of the patella. | To extend the leg. | | 10. Crurceus (M) | From the outer and anterior part of the lesser trochanter. | Into the upper part of the patella. | To extend the leg. | | 11. Pectinalis | From the anterior edge of the os pubis, or pectinis, as it is sometimes called. | Into the upper and fore part of the linea aspera. | To draw the thigh inwards, upwards, and to roll it a little outwards. | | 12. Adductor longus | From the upper and fore part of the os pubis. | Near the middle and back part of the linea aspera. | To draw the thigh inwards, upwards, and to roll it a little outwards. | | 13. Adductor brevis | From the fore part of the ramus of the os pubis. | Into the inner and upper part of the linea aspera. | To draw the thigh inwards, upwards, and to roll it a little outwards. | | 14. Adductor magnus | From the lower and fore part of the ramus of the os pubis. | Into the whole length of the linea aspera. | To move the thigh outwards in an oblique direction, and likewise to bend and draw it inwards. | | 15. Obturator externus| From part of the obturator ligament, and the inner half of the circumference of the foramen thyroideum. | Into the os femoris near the root of the great trochanter. | Muscles |

(k) Spigelius was the first who gave this the name of sartorius, or the taylor's muscle, from its use in crossing the legs.

(r) The vastus externus, vastus internus, and crurceus, are so intimately connected with each other, that some anatomists have been induced to consider them as a triceps, or single muscle with three heads.

(s) Under the crurceus we sometimes meet with two small muscles, to which Albimus has given the name of sub-crurcei. They terminate on each side of the patella, and prevent the capsular ligament from being pinched. When they are wanting, which is very often the case, some of the fibres of the crurceus are found adhering to the capsule.

(t) This and the two following muscles have been usually, but improperly, considered as forming a single muscle with three heads, and on that account named triceps femoris. ### ANATOMY

#### Muscles on the leg:

| Name | Origin | Insertion | Use | |-----------------------|----------------------------------------------------------------------|--------------------------------------------------------------------------|------------------------------------------| | 1. Gastrocnemius (o) | By two heads; one from the inner condyle, the other from the outer condyle, of the os femoris. | By a great round tendon, common to this and the following muscle. | To extend the foot. | | 2. Gastrocnemius (p) | By two heads; one from the back part of the head of the fibula, the other from the upper and back part of the tibia. | By a large tendon (the tendo achillis), common to this and the former muscle, into the lower and back part of the os calcis. | To extend the foot. | | 3. Plantaris (q) | From the upper and posterior part of the outer condyle of the os femoris. | Into the inside of the back part of the os calcis. | To assist in extending the foot. | | 4. Popliteus (r) | From the outer condyle of the thigh. | Into the upper and inner part of the tibia. | To assist in bending the leg and rolling it inwards. | | 5. Flexor longus digitorum pedis (s) | From the upper and inner part of the tibia. | By four tendons, which, after passing through the perforations in those of the flexor digitorum brevis, are inserted into the last bone of all the toes, except the great toe. | To bend the last joint of the toe. | | 6. Flexor longus pollicis pedis. | From the back part, and a little below the head of the fibula. | Into the last bone of the great toe. | To bend the great toe. | | 7. Tibialis posticus. | From the back part, and outer edge of the tibia, and likewise from the interosseous ligament and adjacent part of the fibula. | Into the inner and upper part of the os naviculare and side of the os cuneiforme medium. | To move the foot inwards. | | 8. Peroneus longus. | From the outer side of the head of the tibia, and also from the upper, anterior, and outer part of the perone or fibula, to which it adheres for a considerable way down. | Into the metatarsal bone of the great toe. | To move the foot outwards. | | 9. Peroneus brevis. | From the outer and before part of the fibula. | Into the metatarsal bone of the little toe. | To assist the last described muscle. |

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(o) *Gastrocnemius*, *surgo*, "the calf of the leg."

(p) This muscle is by some anatomists named *soleus*, on account of its being shaped like the sole-fish.

(q) This muscle has gotten the name of *plantaris*, from its being supposed to furnish the aponeurosis that covers the sole of the foot; but it does not in the least contribute to the formation of that tendinous expansion.

(r) So called on account of its situation at the ham (*poples*).

(s) This muscle, about the middle of the foot, unites with a fleshy mass, which, from its having first been described by Sylvius, is usually called *massa carnica Jacobi Sylvii*. ### ANATOMY

| Name | Origin | Insertion | Use | Of the Muscles | |-------------------------------|------------------------------------------------------------------------|---------------------------------------------------------------------------|----------------------------------------------------------------------|----------------| | **10. Extensor longus digitorum pedis.** | From the upper, outer, and fore part of the tibia, interosseous ligament, and inner edge of the fibula. | By four tendons into the first joint of the smaller toes. | To extend the toes. | | | **II. Peroneus tertius.** | From the fore part of the lower half of the fibula, and from the interosseous ligament. | Into the metatarsal bone of the little toe. | To bend the foot. | | | **12. Tibialis anticus.** | From the upper and fore part of the tibia. | Into the os cuneiforme internum. | To bend the foot. | | | **13. Extensor proprius pollicis pedis.** | From the upper and fore part of the tibia. | Into the convex surface of the bones of the great toe. | To extend the great toe. | |

**Muscles on the foot,**

| **1. Extensor brevis digitorum pedis.** | From the upper and anterior part of the os calcis. | By four tendons; one of which joins the tendon of the extensor longus pollicis, and the other three the tendons of the extensor digitorum longus. | To extend the toes. | | | **2. Flexor brevis digitorum pedis.** | From the lower part of the os calcis. | By four tendons, which, after affording a passage to those of the flexor longus, are inserted into the second phalanx of each of the small toes. | To bend the second joint of the toes. | | | **3. Abductor pollicis pedis.** | From the inner and lower part of the os calcis. | Into the first joint of the great toe. | To move the great toe from the other toes. | | | **4. Abductor minimi digiti.** | From the outer tubercle of the os calcis, the root of the metatarsal bone of the little toe, and also from the aponeurosis plantaris. | Into the outer side of the first joint of the little toe. | To draw the little toe outwards. | | | **5. Lumbricales pedis.** | From the tendons of the flexor longus digitorum pedis. | Into the tendinous expansion at the upper part of the toes. | To draw the toes in wards. | | | **6. Flexor brevis pollicis pedis.** | From the inferior and anterior part of the os calcis, and also from the inferior part of the os cuneiformeexternum. | By two tendons into the first joint of the great toe. | To bend the first joint of the great toe. | | | **7. Adductor pollicis pedis.** | From the near roots of the metatarsal bones of the 2d, 3d, and 4th toes. | Into the outer os sesamoideum, or first joint of the great toe. | To draw the great toe nearer to the rest, and also to bend it. | | | **8. Transversales pedis.** | From the outer and under part of the anterior end of the metatarsal bone of the little toe. | Into the inner os sesamoideum, and anterior end of the metatarsal bone of the great toe. | To contract the foot. | |

9. Flexor

Name. Origin. Insertion. Use.

9. Flexor brevis minimi digiti pedis. From the basis of the metatarsal bone of the little toe. Into the first joint of the little toe. To bend the little toe.

10. Interossei pedis interni (r). Situated between the metatarsal bones.

11. Interossei externi (u).

EXPLANATION OF PLATES XXV. and XXVI.

PLATE XXV.

Fig. 1. The Muscles immediately under the common teguments on the anterior part of the body are represented on the right side; and on the left side the muscles are seen which come in view when the exterior ones are taken away.

A, the frontal muscle. B, The tendinous aponeurosis which joins it to the occipital; hence both named occipito-frontalis. C, Attollens aurem. D, The ear. E, Anterior auris. FF, Orbicularis palpebrarum. G, Levator labii superioris alaeque nasi. H, Levator anguli oris. I, Zygomaticus minor. K, Zygomaticus major. L, Masseter. M, Orbicularis oris. N, Depressor labii inferioris. O, Depressor anguli oris. P, Buccinator. QQ, Platysma myoides. RR, Sterno-cleido-mastoideus. S, Part of the trapezius. T, Part of the scaleni.

SUPERIOR EXTREMITY.—U, Deltoides. V, Pectoralis major. W, Part of the latissimus dorsi. XX, Biceps flexor cubiti. YY, Part of the brachialis externus. ZZ, The beginning of the tendinous aponeurosis (from the biceps), which is spread over the muscles of the fore-arm. aa, Its strong tendon inserted into the tubercle of the radius. bb, Part of the brachialis internus. cc, Pronator radii teres. dd, Flexor carpi radialis. ee, Part of the flexor carpi ulnaris. ff, Palmaris longus. gg, Aponeurosis palmaris. ss, Palmaris brevis. ii, Ligamentum carpi annulare. 22, Abductor minimi digiti. ii, Supinator radii longus. jj, The tendons of the thumb. kk, Abductor pollicis. ll, Flexor pollicis longus. mm, The tendons of the flexor sublimis perforatus, profundus perforans, and lumbricales.—The sheaths are entire in the right hand,—in the left cut open, to show the tendons of the flexor profundus perforating the sublimis.

MUSCLES not referred to—in the left superior extremity.—nn, Pectoralis minor, seu serratus anticus minor. oo, The two heads of (xx) the biceps. pp, Coracobrachialis. qq, The long head of the triceps extensor cubiti. rr, Teres major. ss, Subscapularis. tt, Extensors radiales. uu, Supinator brevis. vv, The cut extremity of the pronator teres. ww, Flexor sublimis perforatus. xx, Part of the flexor profundus. yy, Flexor pollicis longus. zz, Part of the flexor pollicis brevis; 4, Abductor minimi digiti. 5, The four lumbricales.

TRUNK.—6, Serrated extremities of the serratus anticus major. 77, Obliquus externus abdominis. 88, The linea alba. 9, The umbilicus. 10, Pyramidis. 11, The spermatic cord. On the left side it is covered by the cremaster. 12, Rectus abdominis. 13, Obliquus internus. 14, Intercostal muscles.

INFERIOR EXTREMITIES.—aa, The gracilis. bb, Part of the triceps. cc, Pectinalis. dd, Psoas magnus. ee, Iliacus internus. ff, Part of the gluteus medius. gg, Part of the gluteus minimus. hh, Cut extremity of the rectus cruris. ii, Vastus externus. kk, Tendon of the rectus cruris. ll, Vastus externus. * Sartorius muscle. ** Fleshy origin of the tensor vaginae femoris or membranous. Its tendinous aponeurosis covers (i) the vastus externus in the right side. mm, Patella. nn, Ligament or tendon from it to the tibia. oo, Rectus cruris. pp, Cruraces. qq, The tibia. rr, Part of the gemellus or gastrocnemius externus. ss, Part of the soleus or gastrocnemius internus. tt, Tibialis anticus. uu, Tibialis posticus. vv, Peronaei muscles. ww, Extensor longus digitorum pedis. xx, Extensor longus pollicis pedis. yy, Abductor pollicis pedis.

FIG. 2. The Muscles, Glands, &c. of the left Side of the Face and Neck, after the common Teguments and Platysma myoides have been taken off.

aa, The frontal muscle. bb, Temporalis and temporal artery. cc, Orbicularis palpebrarum. dd, Levator labii superioris alaeque nasi. ee, Levator anguli oris. ff, Zygomaticus. gg, Depressor labii inferioris. hh, Depressor anguli oris. ii, Buccinator. kk, Masseter. ll, Parotid gland. mm, Its duct. nn, Sterno-cleido-mastoideus. oo, Part of the trapezius. pp, Sterno-hyoides. qq, Sterno-thyroides. rr, Omo hyoides. ss, Levator scapulae. tt, Scaleni. uu, Part of the splenius.

FIG. 3. The Muscles of the Face and Neck in view after the exterior ones are taken away.

aa, Corrugator supercilii. bb, Temporalis. cc, Tendon of the levator palpebrae superioris. dd, Tendon of the orbicularis palpebrarum. ee, Masseter. ff, Buccinator. gg, Levator anguli oris. hh, Depressor labii superioris alaeque nasi. ii, Orbicularis oris. kk, Depressor anguli oris. ll, Muscles of the os hyoides. mm, Sterno-cleido masteideus.

(t) The interossei interni are three in number; their use is to draw the smaller toes towards the great toe. (u) The interossei externi are four in number; the first serves to move the fore toe towards the great toe; the rest move the toes outwards. All the interossei assist in extending the toes. Fig. 4. Some of the Muscles of the Os Hyoides and Submaxillary Gland.

a, Part of the masseter muscle. b, Posterior head of the digastric. c, Its anterior head. dd, Sternohyoides. e, Omo-hyoides. f, Stylo-hyoides. g, Submaxillary gland in situ.

Fig. 5. The Submaxillary Gland and Duct.

a, Musculus mylo-hyoides. b, Hyo-glossus. c, Submaxillary gland extra situm. d, Its duct.

Plate XXVI.

Fig. 1. The Muscles immediately under the common teguments on the posterior part of the body are represented in the right side; and on the left side the muscles are seen which come into view when the exterior ones are taken away.

Head.—AA, Occipito-frontalis. B, Attollens aurum. C, Part of the orbicularis palpebrarum. D, Masseter. E, Pterygoideus internus.

Trunk.—Right side. FFF, Trapezius seu cucullaris. GGGG, Latissimus dorsi. H, Part of the obliquus externus abdominis.

Trunk.—Left side. I, Splenius. K, Part of the complexus. L, Levator scapulae. M, Rhomboideus. NN, Scratus posticus inferior. O, Part of the longissimus dorsi. P, Part of the sacro-lumbalis. Q, Part of the semi-spinalis dorsi. R, Part of the serratus anterior major. S, Part of the obliquus internus abdominis.

Superior Extremity.—Right side. T, Deltoides. U, Triceps extensor cubiti. V, Supinator longus. WW, Extensors carpi radialis longior and brevior. XX, Extensor carpi ulnaris. YY, Extensor digitorum communis. Z, Abductor indicis. i 2 3, Extensors pollicis.

Superior Extremity.—Left side. a, Supra-spinatus. b, Infra-spinatus. c, Teres minor. d, Teres major. e, Triceps extensor cubiti. ff, Extensors carpi radiales. g, Supinator brevis. h, Indicato. i 2 3, Extensors pollicis. i, Abductor minimi digiti. k, Interossei.

Inferior Extremity.—Right side. l, Gluteus maximus. m, Part of the gluteus medius. n, Tensor vaginae femoris. o, Gracilis. pp, Adductor femoris magnus. q, Part of the vastus intermus. r, Semimembranosus. s, Semitendinosus. t, Long head of the biceps flexor cruris. uu, Gastrocnemius externus seu gemellus. v, Tendo Achillis. w, Solcus seu gastrocnemius internus. xx, Peronaeus longus and brevis. y, Tendons of the flexor longus digitorum pedis;—and under them * flexor brevis digitorum pedis. z, Abductor minimi digiti pedis.

Inferior Extremity.—Left side. m, n, o, p, p, q, r, s, t, v, w, x, y, z, Point the same parts as in the right side. a, Pyriformis. bb, Gemini. cc, Obturator internus. d, Quadratus femoris. e, Coccygeus. f, The short head of the biceps flexor cruris. gg, Plantaris. h, Popliteus. i, Flexor longus pollicis pedis.

Fig. 2. The Palm of the Left Hand after the common Teguments are removed, to show the Muscles of the Fingers.

a, Tendon of the flexor carpi radialis. b, Tendon of the flexor carpi ulnaris. c, Tendons of the flexor sublimis perforatus, profundus perforans, and lumbricales. d, Abductor pollicis. ee, Flexor pollicis longus. f, Flexor pollicis brevis. g, Palmaris brevis. h, Abductor minimi digiti. i, Ligamentum carpi annulare. k, A probe put under the tendons of the flexor digitorum sublimis; which are perforated by l, the flexor digitorum profundus. mmmm, Lumbricales. n, Adductor pollicis.

Fig. 3. A Fore view of the Foot and tendons of the Flexores Digitorum.

a, Cut extremity of the tendo Achillis. b, Upper part of the astragalus. c, Os calcis. d, Tendon of the tibialis anticus. e, Tendon of the extensor pollicis longus. f, Tendon of the peronaeus brevis. g, Tendons of the flexor digitorum longus, with the nonus Vesalii. hb, The whole of the flexor digitorum brevis.

Fig. 4. Muscles of the Anus.

aa, An outline of the buttocks, and upper part of the thighs. b, The testes contained in the scrotum. cc, Sphincter ani. d, Anus. e, Levator ani. ff, Erector penis. gg, Accelerator urinæ. h, Corpus cavernosum urethre.

Fig. 5. Muscles of the Penis.

aa, b, d, cc, ff, h, Point the same as in fig. 4. c, Sphincter ani. gg, Transversalis penis.

CHAP. III. OF THE ABDOMEN, OR LOWER BELLY.

The abdomen, or lower belly, extends from the lower extremity of the sternum, or the hollow usually called the pit of the stomach, and more properly scrobiculus cordis, to the lower part of the trunk.

It is distinguished into three divisions called regions; of these, the upper one, which is called the epigastric region, begins immediately under the sternum, and extends to within two fingers breadth of the navel, where the middle or umbilical region begins, and reaches to the same distance below the navel. The third, which is called the hypogastric, includes the rest of the abdomen, as far as the os pubis.

Each of these regions is subdivided into three others; two of which compose the sides, and the other the middle part of each region.

Vol. II. Part I. After having removed the skin, adipose membrane, and abdominal muscles, we discover the peritoneum or membrane that envelopes all the viscera of the lower belly. This being opened, the first part that presents itself is the omentum or cawl, floating on the surface of the intestines, which are likewise seen everywhere loose and moist, and making a great number of circumvolutions through the whole cavity of the abdomen. The stomach is placed in the epigastric region, and under the stomach is the pancreas. The liver fills the right hypochondrium, and the spleen is situated in the left. The kidneys are seen about the middle of the lumbar region, and the urinary bladder and parts of generation are seated in the lower division of the belly.

**Sect. I. Of the Peritoneum.**

The peritoneum is a strong simple membrane, by which all the viscera of the abdomen are surrounded, and in some measure supported. Many anatomical writers, particularly Winslow, have described it as being composed of two distinct membranous laminae; but their description seems to be erroneous: what perhaps appeared to be a second lamina, being found to be simply a cellular coat, which sends off productions to the blood vessels passing out of the abdominal cavity. The aorta and vena cava likewise derive a covering from the same membrane, which seems to be a part of the cellular membrane we have already described.

The peritoneum, by its productions and reduplications, envelopes the greatest part of the abdominal viscera. It is soft, and capable of considerable extension; and is kept smooth and moist by a vapour, which is constantly exhaling from its inner surface, and is returned again into the circulation by the absorbents.

This moisture not only contributes to the softness of the peritoneum, but prevents the attrition, and other ill effects, which would otherwise probably be occasioned by the motion of the viscera upon each other.

When this fluid is supplied in too great a quantity, or the absorbents become incapable of carrying it off, it accumulates, and constitutes an ascites or dropsy of the belly; and when by any means the exhalation is discontinued, the peritoneum thickens, becomes diseased, and the viscera are sometimes found adhering to each other.

The peritoneum is not a very vascular membrane. In a sound state it seems to be ended with little or no feeling, and the nerves that pass through it appear to belong to the abdominal muscles.

**Sect. II. Of the Omentum.**

The omentum, epiploon, or cawl, is a double membrane, produced from the peritoneum. It is interlarded with fat, and adheres to the stomach, spleen, duodenum, and colon; from thence hanging down loose and floating on the surface of the intestines. Its size is different in different subjects. In some it descends as low as the pelvis, and it is commonly longer at the left side than the right.

This part, the situation of which we have just now described, was the only one known to the ancients under the name of epiploon; but at present we distinguish three omenta, viz. omentum magnum colico-gastricum, omentum parvum hepatico-gastricum, and omentum colicum. They all agree in being formed of two very delicate laminae, separated by a thin layer of cellular membrane.

The omentum magnum colico-gastricum, of which we have already spoken, derives its arteries from the splenic and hepatic. Its veins terminate in the vena porta. Its nerves, which are very few, come from the splenic and hepatic plexus.

The omentum parvum hepatico-gastricum abounds less with fat than the great epiploon. It begins at the upper part of the duodenum, extends along the lesser curvature of the stomach as far as the oesophagus, and terminates about the neck of the gall-bladder, and behind the left ligament of the liver, so that it covers the lesser lobe; near the beginning of which we may observe a small opening, first described by Winslow, through which the whole pouch may easily be distended with air (x). The vessels of the omentum parvum are derived chiefly from the coronary stomachic arteries and veins.

The omentum colicum begins at the fore part of the cæcum and right side of the colon. It appears as a hollow conical appendage to these intestines, and usually terminates at the back of the omentum magnum. It seems to be nothing more than a membranous coat of the cæcum and colon, assuming a conical shape when distended with air.

The uses of the omentum are not yet satisfactorily determined. Perhaps by its softness and looseness it may serve to prevent those adhesions of the abdominal viscera, which have been found to take place when the fat of the omentum has been much wasted. Some authors have supposed, that it assists in the preparation of bile; but this is founded merely on conjecture.

**Sect. III. Of the Stomach.**

The stomach is a membranous and muscular bag, in shape not unlike a bagpipe, lying across the upper part of the abdomen, and inclining rather more to the left than the right side.

It has two orifices, one of which receives the end of the oesophagus, and is called the cardia, and sometimes the left and upper orifice of the stomach; though its situation is not much higher than the other, which is styled the right and inferior orifice, and more commonly the pylorus; both these openings are more elevated than the body of the stomach.

The aliment passes down the oesophagus into the stomach through the cardia, and after having undergone

(x) This membranous bag, though exceedingly thin and transparent, is found capable of supporting mercury, thrown into it by the same channel. gone the necessary digestion, passes out at the pylorus where the intestinal canal commences.

The stomach is composed of four tunics or coats, which are so intimately connected together that it requires no little dexterity in the anatomist to demonstrate them. The exterior one is membranous, being derived from the peritoneum. The second is a muscular tunic, composed of fleshy fibres, which are in the greatest number about the two orifices. The third is called the nervous coat, and within this is the villous or velvet-like coat which composes the inside of the stomach.

The two last coats being more extensive than the two first, form the folds, which are observed everywhere in the cavity of this viscus, and more particularly about the pylorus; where they seem to impede the too hasty exclusion of the aliment, making a considerable plait, called valvula pylori.

The inner coat is constantly moistened by a mucus, which approaches to the nature of the saliva, and is called the gastric juice: this liquor has been supposed to be secreted by certain minute glands (γ) seated in the nervous tunic, whose excretory ducts open on the surface of the villous coat.

The arteries of the stomach called the gastric arteries are principally derived from the celiac; some of its veins pass to the splenic, and others to the vena portae; and its nerves are chiefly from the eighth pair or par vagum.

The account given of the tunics of the stomach may be applied to the whole alimentary canal: for both the oesophagus and intestines are, like this viscus, composed of four coats.

Before we describe the course of the aliment, and the uses of the stomach, it will be necessary to speak of other parts which assist in the process of digestion.

Sect. IV. Of the Oesophagus.

The oesophagus or gullet is a membranous and muscular canal, extending from the bottom of the mouth to the upper orifice of the stomach. Its upper part, where the aliment is received, is shaped somewhat like a funnel, and is called the pharynx.

From hence it runs down close to the bodies of the vertebrae as far as the diaphragm, in which there is an opening through which it passes, and then terminates in the stomach about the eleventh or twelfth vertebra of the back.

The oesophagus is plentifully supplied with arteries from the external carotid, bronchial, and superior intercostal arteries; its veins empty themselves into the vena azygos, internal jugular, and mammary veins, &c.

Its nerves are derived chiefly from the eighth pair.

We likewise meet with a mucus in the oesophagus, which everywhere lubricates its inner surface, and tends to assist in deglutition. This mucus seems to be secreted by very minute glands, like the mucus in other parts of the alimentary canal.

Sect. V. Of the Intestines.

The intestines form a canal, which is usually six times longer than the body to which it belongs. This canal extends from the pylorus, or inferior orifice of the stomach, to the anus.

It will be easily understood, that a part of such great length must necessarily make many circumvolutions, to be confined with so many other viscera within the cavity of the lower belly.

Although the intestines are in fact, as we have observed, only one long and extensive canal, yet different parts have been distinguished by different names.

The intestines are first distinguished into two parts, one of which begins at the stomach, and is called the thin or small intestines, from the small size of the canal, when compared with the other part, which is called the large intestines, and includes the lower portion of the canal down to the anus.

Each of these parts has its subdivisions. The small intestines being distinguished into duodenum, jejunum, and ileum, and the larger portion into cecum, colon, and rectum.

The small intestines fill the middle and fore parts of the belly, while the large intestines fill the sides and both the upper and lower parts of the cavity.

The duodenum, which is the first of the small intestines, is so called, because it is about 12 inches long. It begins at the pylorus, and terminates in the jejunum, which is a part of the canal observed to be usually more empty than the other intestines. This appearance give it its name, and likewise serves to point out where it begins.

The next division is the ileum, which of itself exceeds the united length of the duodenum and jejunum, and has received its name from its numerous circumvolutions. The large circumvolution of the ileum covers the first of the large intestines called the cecum (z), which seems properly to belong to the colon, being a kind of pouch of about four fingers in width, and nearly of the same length, having exteriorly a little appendix, called appendix cæci.

The cecum is placed in the cavity of the os ilium on the right side, and terminates in the colon, which is the largest of all the intestines.

This intestine ascends by the right kidney to which it is attached, passes under the hollow part of the liver, and the bottom of the stomach, to the spleen, to which it is likewise secured, as it is also to the left kidney; and from thence passes down towards the os sacrum,

(y) Heister, speaking of these glands, very properly says, "in porcis facile, in homine raro observantur;" for although many anatomical writers have described their appearance and figure, yet they do not seem to have been hitherto satisfactorily demonstrated in the human stomach; and the gastric juice is now more generally believed to be derived from the exhalant arteries of the stomach.

(z) Anatomists have differed with respect to this division of the intestines.—The method here followed is now generally adopted; but there are authors who allow the name of cecum only to the little appendix, which has likewise been called the vermiform appendix, from its resemblance to a worm in size and length. where, from its straight course, the canal begins to take the name of rectum.

There are three ligamentous bands extending through the whole length of the colon, which by being shorter than its two inner coats, serve to increase the plaiting on the inner surface of this gut.

The anus, which terminates the intestinum rectum, is furnished with three muscles; one of these is composed of circular fibres, and from its use in shutting the passage of the anus is called sphincter ani.

The other two are the levatores ani, so called, because they elevate the anus after defecation. When these by palsy, or any other disease, lose the power of contracting, the anus prolapses; and when the sphincter is affected by similar causes, the faeces are voided involuntarily.

It has been already observed that the intestinal canal is composed of four tunics; but it remains to be remarked, that here, as in the stomach, the two inner tunics being more extensive than the other two, form the plaiting which are to be seen in the inner surface of the intestines, and are called valvulae conniventes.

Some authors have considered these plaitings as tending to retard the motion of the faeces, in order to afford more time for the separation of the chyle; but there are others who attribute to them a different use; they contend, that these valves, by being naturally inclined downwards, cannot impede the descent of the faeces, but that they are intended to prevent their return upwards.

They are probably destined for both these uses; for although these folds incline to their lower side, yet the inequalities they occasion in the canal are sufficient to retard in some measure the progressive motion of the faeces, and to afford a greater surface for the absorption of chyle; and their natural position seems to oppose itself to the return of the aliment.

Besides these valvulae conniventes, there is one more considerable than the rest, called the valve of the colon; which is found at that part of the canal where the intestinum ileum is joined to the colon. This valve permits the alimentary pulp to pass downwards, but serves to prevent its return upwards; and it is by this valve that clusters are prevented from passing into the small intestines (Y).

Of the little vermiform appendix of the cæcum, it will be sufficient to say, that its uses have never yet been ascertained. In birds we meet with two of these appendices.

The intestines are lubricated by a constant supply of mucus, which is probably secreted by very minute follicles (z). This mucus promotes the descent of the alimentary pulp, and in some measure defends the inner surface of the intestines from the irritation to which it would, perhaps, otherwise be continually exposed from the aliment; and which, when in a certain degree, excites a painful disorder called colic, a name given to the disease, because its most usual seat is in the intestinum colon.

The intestines are likewise frequently distended with air, and this distension sometimes occasions pain, and constitutes the flatulent colic.

The arteries of the intestines are continuations of the mesenteric arteries, which are derived in two considerable branches from the aorta.—The redundant blood is carried back into the vena portae.

In the rectum the veins are called hemorrhoidal, and are there distinguished into internal and external: the first are branches of the inferior mesenteric vein, but the latter pass into other veins. Sometimes these veins are distended with blood from obstructions, from weakness of their coats, or from other causes, and what we call the hemorrhoids takes place. In this disease they are sometimes ruptured; and the discharge of blood which consequently follows has probably occasioned them to be called hemorrhoidal veins.

The nerves of the intestines are derived from the eighth pair.

**Sect. VI. Of the Mesentery.**

The name of the mesentery implies its situation amidst the intestines. It is in fact a part of the peritoneum, being a reduplication (A) of that membrane from each side of the lumbar vertebrae, to which it is firmly attached, so that it is formed of two laminae connected to each other by cellular membrane.

The intestines, in their different circumvolutions, form a great number of arches, and the mesentery accompanies them through all these turns; but by being attached

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(y) This is not invariably the case; for the contents of a cluster have been found not only to reach the small intestines, but to be voided at the mouth. Such instances, however, are not common.

(z) Some writers have distinguished these glands into military, lenticular, &c. Brunner and Peyer were the first anatomists who described the glands of the intestines, and their descriptions were chiefly taken from animals, these glandular appearances not seeming to have been hitherto satisfactorily pointed out in the human subject. It is now pretty generally believed, that the mucus which everywhere lubricates the alimentary canal, is exhaled from the minute ends of arteries; and that these extremities first open into a hollow vesicle, from whence the deposited juice of several branches flows out through one common orifice.

(A) He who only reads of the reduplication of membranes, will perhaps not easily understand how the peritoneum and pleura are reflected over the viscera in their several cavities; for one of these serves the same purpose in the thorax that the other does in the abdomen. This disposition, for the discovery of which we are indebted to modern anatomists, constitutes a curious part of anatomical knowledge; but the student, unaided by experience, and assisted only by what the limits of this work would permit us to say on the occasion, would probably imbibe only confused ideas of the matter; and it will perfectly answer the present purpose, if he considers the mesentery as a membrane attached by one of its sides to the lumbar vertebrae, and by the other to the intestines. attached only to the hollow part of each arch, it is found to have only a third of the extent of the intestines.

That part of the membrane which accompanies the small intestines is the mesentery, properly so called; but those parts of it which are attached to the colon and rectum are distinguished by the names of meso-colon and meso-rectum.

There are many conglomerate glands dispersed through this double membrane, through which the lacteals and lymphatics pass in their way to the thoracic duct. The blood-vessels of the mesentery were described in speaking of the intestines.

This membrane, by its attachment to the vertebre, serves to keep the intestines in their natural situation. The idea usually formed of the colic called viscerere, is perfectly erroneous; it being impossible that the intestines can be twisted; as many suppose they are, in that disease, their attachment to the mesentery effectually preventing such an accident—but a disarrangement sometimes takes place in the intestinal canal itself, which is productive of disagreeable and sometimes fatal consequences. This is by an intussusception of the intestine, an idea of which may be easily formed, by taking the finger of a glove, and involving one part of it within the other.

If inflammation takes place, the stricture in this case is increased, and the peristaltic motion of the intestines (by which is meant the progressive motion of the faeces downwards) is inverted, and what is called the iliac passion takes place. The same effects may be occasioned by a descent of the intestine, or of the omentum either with it or by itself, and thus constituting what is called a hernia or rupture; a term by which in general is meant the falling down or protrusion of any part of the intestine or omentum, which ought naturally to be contained within the cavity of the belly.

To convey an idea of the manner in which such a descent takes place, it will be necessary to observe, that the lower edge of the tendon of the musculus obliquus externus, is stretched from the fore part of the os ilium or haunch bone to the os pubis, and constitutes what is called Poupart's or Follopius's ligament, forming an opening, through which pass the great crural artery and vein. Near the os pubis the same tendinous fibres are separated from each other, and form an opening on each side, called the abdominal ring, through which the spermatic vessels pass in men, and the ligamenta uteri in women. In consequence of violent efforts, or perhaps of natural causes, the intestines are found sometimes to pass through these openings; but the peritoneum which encloses them, when in their natural cavity, still continues to surround them even in their descent. This membrane does not become torn or lacerated by the violence, as might be easily imagined; but its dilatability enables it to pass out with the viscus, which it encloses as it were in a bag, and thus forms what is called the hernial sac.

If the hernia be under Poupart's ligament, it is called femoral; if in the groin inguinal (B); and scrotal, if in the scrotum. Different names are likewise given to the hernia as the contents of the sac differ, whether of omentum only, or intestine, or both—but these definitions more properly belong to the province of surgery.

Sect. VII. Of the Pancreas.

The pancreas is a conglomerate gland, placed behind the bottom of the stomach, towards the first vertebra of the loins; shaped like a dog's tongue, with its point stretched out towards the spleen, and its other end extending towards the duodenum. It is about eight fingers breadth in length, two or three in width, and one in thickness.

This viscus, which is of a yellowish colour, somewhat inclining to red, is covered with a membrane which it derives from the peritoneum. Its arteries, which are rather numerous than large, are derived chiefly from the splenic and hepatic, and its veins pass into the veins of the same name.—Its nerves are derived from the intercostal.

The many little glands of which it has been observed the pancreas is composed, all serve to secrete a liquor called the pancreatic juice, which in its colour, consistence, and other properties, does not seem to differ from the saliva. Each of these glands sends out a little excretory duct, which, uniting with others, help to form larger ducts; and all these at last terminate in one common excretory duct (first discovered by Virtsungus in 1642), which runs through the middle of the gland, and is now usually called ductus pancreaticus Virtsungii. This canal opens into the intestinum duodenum, sometimes by the same orifice with the biliary duct, and sometimes by a distinct opening. The liquor it discharges being of a mild and insipid nature, serves to dilute the alimentary pulp, and to incorporate it more easily with the bile.

Sect. VIII. Of the Liver.

The liver is a viscus of considerable size, and of a reddish colour; convex superiorly and anteriorly where it is placed under the ribs and diaphragm, and of an unequal form posteriorly. It is chiefly situated in the right hypochondrium, and under the false ribs; but it likewise extends into the epigastric region, where it borders upon the stomach. It is covered by a production of the peritoneum, which serves to attach it by three of its reduplications to the false ribs. These reduplications are called ligaments, though very different in their texture from what are called by the same name in other parts of the body. The umbilical cord, too, which in the fetus is pervious, gradually becomes a simple ligament after birth; and by passing to the liver, serves likewise to secure it in its situation.

At the posterior part of this organ, where the umbilical vessels enter, it is found divided into two lobes. Of these, the largest is placed in the right hypochondrium; the other, which covers part of the stomach, is called the little lobe. All the vessels which go to the liver pass in at the fissure we have mentioned; and the production of the peritoneum, which invests the liver, was described by Glisson, an English anatomist, as accompanying them in their passage, and surrounding

(b) The hernia congenita will be considered with the male organs of generation, with which it is intimately connected.

The surrounding them like a glove; hence this production has been commonly known by the name of capula of Glisson: but it appears to be chiefly a continuation of the cellular membrane which covers the vena portae ventralis.

The liver was considered by the ancients as an organ destined to prepare and perfect the blood; but later discoveries have proved, that this opinion was wrong, and that the liver is a glandular substance formed for the secretion of the bile.

The blood is conveyed to the liver by the hepatic artery and the vena portae. This is contrary to the mode of circulation in other parts, where veins only serve to carry off the redundant blood; but in this viscus the hepatic artery, which is derived from the celiac, is principally destined for its nourishment; and the vena portae, which is formed by the union of the veins from most of the abdominal viscera, furnishes the blood from which the bile is chiefly to be separated: so that these two series of vessels serve very distinct purposes. The vena portae, as it is ramified through the liver, performs the office both of a vein and an artery; for like the former it returns the blood from the extremities of arteries, while as the latter it prepares it for secretion.

The nerves of the liver are branches of the intercostal and par vagum. The bile, after being separated from the mass of blood, in a manner of which mention will be made in another place, is conveyed out of this organ by very minute excretory ducts, called porti biliaris; these uniting together like the excretory ducts in the pancreas, gradually form larger ones, which at length terminate in a considerable channel called ductus hepaticus.

Sect. IX. Of the Gall-Bladder.

The gall-bladder is a little membranous bag, shaped like a pear, and attached to the posterior and almost inferior part of the great lobe of the liver.

It has two tunics; of which the exterior one is a production of the peritoneum. The interior, or villous coat, is supplied with a mucus that defends it from the acrimony of the bile. These two coverings are intimately connected by means of cellular membrane, which from its firm glistening appearance has generally been spoken of as a muscular tunic.

The gall-bladder is supplied with blood-vessels from the hepatic arteries. These branches are called the cystic arteries, and the cystic veins carry back the blood.

Its nerves are derived from the same origin as those of the liver.

The neck of the gall-bladder is continued in the form of a canal called ductus cysticus, which soon unites with the ductus hepaticus we described as the excretory duct of the liver; and forming one common canal, takes the name of ductus choledochus communis, through which both the cystic and hepatic bile are discharged into the duodenum. This canal opens into the intestine in an oblique direction, first passing through the exterior tunic, and then piercing the other coats after running between each of them a very little way. This economy serves two useful purposes—to promote the discharge of bile, and to prevent its return.

The bile may be defined to be a natural liquid soap, of the bile, somewhat unctuous and bitter, and of a yellowish colour, which easily mixes with water, oil, and vinous spirits, and is capable of dissolving resinous substances. From some late experiments made by M. Cadet *, it * Mem. de l'Acad. des Sciences, appears to be formed of an animal oil, combined with the alkaline base of sea salt, a salt of the nature of milk, and a calcareous earth which is slightly ferruginous.

Its definition seems sufficiently to point out the uses for which it is intended (c). It blends the alimentary mass, by dividing and attenuating it; corrects the too great disposition to ascency, which the aliment acquires in the stomach; and, finally, by its acrimony, tends to excite the peristaltic motion of the intestines.

After what has been said, it will be conceived that there are two sorts of bile: one of which is derived immediately from the liver through the hepatic duct, and the other from the gall-bladder. These two biles, however, do not essentially differ from each other. The hepatic bile indeed is milder, and more liquid than the cystic, which is constantly thicker and yellower; and by being bitterer, seems to possess greater activity than the other.

Every body knows the source of the hepatic bile, that it is secreted from the mass of blood by the liver; but the origin of the cystic bile has occasioned no little controversy amongst anatomical writers. There are some who contend, that it is separated in the substance of the liver, from whence it passes into the gall-bladder through particular vessels. In deer, and in some other quadrupeds, as well as in several birds and fishes, there is an evident communication, by means of particular vessels, between the liver and the gall-bladder. Bianchi, Winslow, and others, have asserted the existence of such vessels in the human subject, and named them hepatico-cystic ducts; but it is certain that no such ducts exist.—In obstructions of the cystic duct, the gall-bladder has been found shrivelled and empty: so that we may consider the gall-bladder as a reservoir of hepatic bile; and that it is an established fact, that the whole of the bile contained in the gall-bladder is derived from the liver; that it passes from the hepatic or the cystic duct, and from that to the gall-bladder. The difference in the colour, consistence, and taste of the bile, is merely the consequence of stagnation and absorption. When the stomach is distended with aliment, this reservoir undergoes a certain degree of compression, and the bile passes out into the intestinal canal; and in the efforts to vomit, the gall-bladder seems to be constantly affected, and at such times discharges itself of its contents.

Sometimes

(c) The ancients, who were not acquainted with the real use of the liver, considered the bile as an excrementitious and useless fluid. Sometimes the bile concretes in the gall-bladder, so as to form what are called gall-stones (D). When these concretions pass into the cystic duct, they sometimes occasion exquisite pain, by distending the canal in their way to the duodenum; and by lodging in the ductus choledochus communis, and obstructing the course of the bile, this fluid will be absorbed, and by being carried back into the circulation occasion a temporary jaundice.

**Sect. X. Of the Spleen.**

The spleen is a soft and spongy viscus, of a bluish colour, and about five or six fingers breadth in length, and three in width, situated in the left hypochondrium, between the stomach and the false ribs. That side of it which is placed on the side of the ribs is convex; and the other, which is turned towards the stomach, is concave.

The splenic artery, which is a branch from the cæliac, supplies this viscus with blood, and a vein of the same name carries it back into the vena portæ.

Its nerves are derived from a particular plexus called the splenic, which is formed by branches of the intercostal nerve, and by the eighth pair, or par vagum.

The ancients, who supposed two sorts of bile, considered the spleen as the receptacle of what they called atra bilis. Havers, who wrote professedly on the bones, determined its use to be that of secreting the synovia; and the late Mr Hewson imagined, that it concurred with the thymus and lymphatic glands of the body in forming the red globules of the blood. All these opinions seem to be equally fanciful. The want of an excretory duct has occasioned the real use of this viscus to be still doubtful. Perhaps the blood undergoes some change in it, which may assist in the preparation of the bile. This is the opinion of the generality of modern physiologists; and the great quantity of blood with which it is supplied, together with the course of its veins into the vena portæ, seem to render this notion probable.

**Sect. XI. Of the Glandulae Renales, Kidneys, and Ureters.**

The glandulae renales, which were by the ancients supposed to secrete the atra bilis, and by them named capsulae atrabiliæ, are two flat bodies of an irregular figure, one on each side between the kidney and the aorta.

In the fetus they are as large as the kidneys; but they do not increase afterwards in proportion to those parts; and in adults and old people they are generally found shrivelled, and much wasted. They have their arteries and veins. Their arteries usually arise from the splenic or the emulgent, and sometimes from the aorta; and their veins go to the neighbouring veins, or to the vena cava. Their nerves are branches of the intercostal.

The use of these parts is not yet perfectly known. In the fetus the secretion of urine must be in a very small quantity, and a part of the blood may perhaps then pass through these channels, which in the adult is carried to the kidneys to supply the matter of urine.

The kidneys are two in number, situated one on the right and the other on the left side in the lumbar region, between the last false rib and the os ilium, by the sides of the vertebrae. Each kidney in its figure resembles a sort of bean, which from its shape is called kidney bean. The concave part of each kidney is turned towards the aorta and vena cava ascendens. They are surrounded by a good deal of fat, and receive a coat from the peritoneum; and when this is removed, a very fine membrane is found investing their substance and the vessels which ramify through them.

Each kidney has a considerable artery and vein, which are called the emulgent. The artery is a branch from the aorta, and the vein passes into the vena cava. Their nerves, which everywhere accompany the blood vessels, arise from a considerable plexus, which is derived from the intercostal.

In each kidney, which in the adult is of a pretty firm texture, there are three substances to be distinguished (E). The outer part is glandular or cortical, beyond this is the vascular or tubular substance, and the inner part is papillary or membranous.

It is in the cortical part of the kidney that the secretion is carried on; the urine being there received from the minute extremities of the capillary arteries, is conveyed out of this cortical substance by an infinite number of very small cylindrical canals or excretory vessels, which constitute the tubular part. These tubes, as they approach the inner substance of the kidney, gradually unite together; and thus forming larger canals, at length terminate in ten or twelve little protuberances called papillæ, the orifices of which may be seen without the assistance of glasses. These papillæ open into a small cavity or reservoir called the pelvis of the kidney, and formed by a distinct membranous bag which embraces the papillæ. From this pelvis the urine is conveyed through a membranous canal which passes out from the hollow side of the kidney, a little below the blood-vessels, and is called ureter.

The ureters are each about as large as a common writing pen. They are somewhat curved in their course from the kidneys, like the letter J, and at length terminate in the posterior and almost inferior part of the bladder, at some distance from each other. They pass into the bladder in the same manner as the ductus choledochus communis passes into the intestineum duodenum, not by a direct passage, but by an oblique course.

(D) These concretions sometimes remain in the gall-bladder without causing any uneasiness. Dr Heberden relates, that a gall-stone, weighing two drachms, was found in the gall-bladder of Lord Bath, though he had never complained of the jaundice, or of any disorder which he could attribute to that cause. Med. Trans. vol. ii.

(E) The kidneys in the fetus are distinctly lobulated; but in the adult they become perfectly firm, smooth, and regular. course between the two coats; so that the discharge of urine into the bladder is promoted, whilst its return is prevented. Nor does this mode of structure prevent the passage of fluids only from the bladder into the ureters, but likewise air—for air thrown into the bladder inflates it, and it continues to be distended if a ligature is passed round its neck; which seems to prove sufficiently that it cannot pass into the ureters.

**Sect. XII. Of the Urinary Bladder.**

The urinary bladder is a membranous and muscular bag of an oblong roundish shape, situated in the pelvis, between the os pubis and intestinum rectum in men, and between the os pubis and uterus in women. Its upper and widest part is usually called the bottom, its narrower part the neck of the bladder; the former is only covered by the peritoneum.

The bladder is formed of three coats, connected together by means of cellular membrane. The external or peritoneal, is only a partial one, covering the upper and back part of the bladder. The middle, or muscular coat, is composed of irritable, and of course muscular fibres, which are most collected around the neck of the bladder, but not so as to form a distinct muscle or sphincter, as the generality of anatomists have hitherto supposed.

The inner coat, though much smoother, has been said to resemble the villous tunic of the intestines, and like that is provided with a mucus, which defends it against the acrimony of the urine.

It will easily be conceived, from what has been said, that the kidneys are two glandular bodies, through which a saline and excrementitious fluid called urine is constantly filtering from the mass of blood.

While only a small quantity of urine is collected in the bladder, it excites no kind of uneasiness: but when a greater quantity is accumulated, so that the bladder is distended in a certain degree, it excites in us a certain sensation, which brings on it were a voluntary contraction of the bladder to promote its discharge.—But this contraction is not effected by the muscular fibres of the bladder alone: for all the abdominal muscles contract in obedience to our will, and press downwards all the viscera of the lower belly; and these powers being united, at length overcome the resistance of the fibres surrounding the neck of the bladder, which dilates and affords a passage to the urine through the urethra.

The frequency of this evacuation depends on the quantity of urine secreted; on the degree of acrimony it possesses; on the size of the bladder, and on its degree of sensibility.

The urine varies much in its colour and contents. These varieties depend on age, sex, climate, diet, and other circumstances. In infants it is generally a clear watery fluid, without smell or taste. As we advance in life, it acquires more colour and smell, and becomes more impregnated with salts. In old people it becomes still more acid and fetid.

In a healthy state it is nearly of a straw colour.—After being kept for some time, it deposits a tartarous matter, which is found to be composed chiefly of earth and salt, and soon incrusts the sides of the vessel in which it is contained. While this separation is taking place, appearances like minute fibres or threads of a whitish colour, may be seen in the middle of the urine, and an oily scum observed floating on its surface. So that the most common appearances of the urine are sufficient to ascertain that it is a watery substance, impregnated with earthy, saline, and oily particles.

The urine is not always voided of the same colour and consistence; for these are found to depend on the proportion of its watery part to that of its other constituent principles.—Its colour and degree of fluidity seem to depend on the quantity of saline and inflammable particles contained in it: so that an increased proportion of those parts will constantly give the urine a higher colour, and add to the quantity of sediment.

The variety in the appearances of the urine depends on the nature and quantity of solid and fluid aliment we take in; and it is likewise occasioned by the different state of the urinary vessels, by which we mean the channels through which it is separated from the blood, and conveyed through the pelvis into the ureters. The causes of calculous concretion in the urinary passages, are to be looked for in the natural constitution of the body, mode of life, &c.

It having been observed, that after drinking any light wine or Spa water, it very soon passed off by urine, it has been supposed by some, that the urine is not altogether conveyed to the bladder by the ordinary course of circulation, but that there must certainly exist some other shorter means of communication, perhaps by certain vessels between the stomach and the bladder, or by a retrograde motion in the lymphatics. But it is certain, that if we open the belly of a dog, press out the urine from the bladder, pass a ligature round the emulgent arteries, and then sew up the abdomen, and give him even the most diuretic liquor to drink, the stomach and other channels will be distended with it, but not a drop of urine will be found to have passed into the bladder; or the same thing happens when a ligature is thrown round the two ureters. This experiment then seems to be a sufficient proof, that all the urine we evacuate is conveyed to the kidneys through the emulgent arteries, in the manner we have described.—It is true, that wine and other liquors promote a speedy evacuation of urine; but the discharge seems to be merely the effect of the stimulus they occasion; by which the bladder and urinary parts are solicited to a more copious discharge of the urine, which was before in the body, and not immediately of that which was last drank; and this increased discharge, if the supply is kept up, will continue: nor will this appear wonderful, if we consider the great capacity of the vessels that go to the kidneys; the constant supply of fresh blood that is essential to health; and the rapidity with which it is incessantly circulated through the heart to all parts of the body.

**Sect. XIII. Of Digestion.**

We are now proceeding to speak of digestion, which seems to be introduced in this place with propriety, after a description of the abdominal viscera, the greater part of which contribute to this function. By digestion is to be understood, the changes the aliment undergoes The mouth, of which every body has a general knowledge, is the cavity between the two jaws, formed anteriorly and laterally by the lips, teeth, and cheeks, and terminating posteriorly in the throat.

The lips and cheeks are made up of fat and muscles, covered by the cuticle, which is continued over the whole inner surface of the mouth, like a fine and delicate membrane.—Besides this membrane, the inside of the mouth is furnished with a spongy and very vascular substance called the gums, by means of which the teeth are secured in their sockets. A similar substance covers the roof of the mouth, and forms what is called the velum pendulum palati, which is fixed to the extremity of the arch formed by the ossa maxillaria and ossa palati, and terminates in a soft, small, and conical body, named uvula; which appears, as it were, suspended from the middle of the arch over the basis of the tongue.

The velum pendulum palati performs the office of a valve between the cavity of the mouth and the pharynx, being moved by several muscles (F).

The tongue is composed of several muscles (G) which enable it to perform a variety of motions for the articulation of the voice; for the purposes of mastication; and for conveying the aliment into the pharynx. Its upper part is covered with papillae, which constitute the organ of taste, and are easily to be distinguished; it is covered by the same membrane that lines the inside of the mouth, and which makes at its inferior part towards its basis a reduplication called frenum.

Posteriorly, under the velum palati, and at the basis of the tongue, is the pharynx; which is the beginning of the cesophagus, stretched out every way, so as to resemble the top of a funnel, through which the aliment passes into the stomach.

The mouth has a communication with the nostrils at its posterior and upper part; with the ears, by the Eustachian tubes; with the lungs, by means of the larynx; and with the stomach, by means of the cesophagus.

The pharynx is constantly moistened by a fluid, secreted by two considerable glands called the tonsils, one on each side of the velum palati. These glands, from their supposed resemblance to almonds, have likewise been called amygdalus.

The mouth is moistened by a considerable quantity of saliva. This fluid is derived from the parotid glands; a name which by its etymology points out their situation to be near the ears. They are two in number, one on each side under the os malae; and they are of the conglomerate kind; being formed of many smaller glands, each of which sends out a very small excretory duct, which unites with the rest, to form one common channel, that runs over the cheek, and piercing the buccinator muscle, opens into the mouth on each side, by an orifice into which a bristle may be easily introduced.

Besides these, the maxillary glands, which are placed near the inner surface of the angle of the lower jaw on each side; the sublingual glands, which are situated at the root of the tongue; the glands of the palate, which are seated in the velum palati; and those of the cheeks, lips, &c. together with many other less considerable ones,—pour the saliva into the mouth through their several excretory ducts.

The saliva, like all the other humours of the body, is found to be different in different people; but in general, it is a limpid and insipid fluid, without smell in healthy subjects; and these properties would seem to prove, that it contains very few saline or inflammable particles.

The uses of the saliva seem to be to moisten and lubricate the mouth, and to assist in reducing the aliment into a soft pulp before it is conveyed into the stomach.

The variety of functions which are constantly performed by the living body, must necessarily occasion continual waste and dissipation of its several parts. A great quantity is every day thrown off by the insensible perspiration and other discharges; and were not these losses constantly recruited by a fresh supply of chyle, the body would soon effect its own dissolution. But nature has very wisely favoured us with organs fitted to produce such a supply; and has at the same time endowed us with the sensations of hunger and thirst, that our attention may not be diverted from the necessary business of nutrition. The sensation of hunger is universally known; but it would perhaps be difficult to describe it perfectly in words. It may, however, be defined to be a certain uneasy sensation in the stomach, which induces us to wish for solid food; and which likewise serves to point out the proper quantity, and time for taking it. In describing the stomach, mention was made of the gastric juice, as everywhere lubricating its inner coat. This humour mixes itself with the aliment in the stomach, and helps to prepare it for its passage into the intestines; but when the stomach is perfectly empty, this same fluid irritates the coats of the stomach itself, and produces the sensation of hunger.

A certain proportion of liquid aliment is required to assist in the process of digestion, and to afford that moisture to the body, of which there is such a constant dissipation. Thirst induces us to take this necessary supply of drink; and the seat of this sensation is in the tongue, fauces, and cesophagus, which from their great sensibility are required to be kept moist: for though the fauces are naturally moistened by the mucous and salival juices; yet the blood, when deprived of its watery part, or rendered acrimonious by any natural causes, never fails particularly to affect these parts, and the whole alimentary canal, and to occasion thirst.—This is the common effect of fevers and of hard labour, by both which too much of the watery part of the blood is dissipated.

It has been observed, that the aliment undergoes some

(f) These are the circumflexus palati, levator palati mollis, palato-pharyngeus, constrictor isthmi faucium, and azigos uvulae.

(g) These are, the genio-glossus, hyo-glossus, lingualis, and stylo-glossus. some preparation in the mouth before it passes into the stomach; and this preparation is the effect of mastication. In treating of the upper and lower jaws, mention was made of the number and arrangement of the teeth. The upper jaw was described as being immovable; but the lower jaw was spoken of as being capable of elevation and depression, and of a grinding motion. The aliment, when first carried into the mouth, is pressed between the teeth of the two jaws, by a very strong and frequent motion of the lower jaw; and the tongue and the cheeks assisting in this process, continue to replace the food between the teeth till it is perfectly divided, and reduced to the consistence of pulp. The incisores and canini divide it first into smaller pieces, but it is between the surfaces of the dentes molares by the grinding motion of the jaw that the mastication is completed.

During this process, the salival glands being gently compressed by the contraction of the muscles that move the lower jaw, pour out their saliva: this helps to divide and break down the food, which at length becomes a kind of pulp, and is then carried over the basis of the tongue into the fauces. But to effect this passage into the oesophagus, it is necessary that the other openings which were mentioned, as having a communication with the mouth as well as the pharynx, should be closed; that none of the aliment, whether solid or liquid, may pass into them, whilst the pharynx alone is dilated to receive it:—And such a disposition actually takes place in a manner we will endeavour to describe.

The trachea arteria, or windpipe, through which the air is conveyed to the lungs, is placed before the oesophagus: in the act of swallowing, therefore, if the larynx (for so the upper part of the trachea is called) is not closed, the aliment will pass into it in its way to the oesophagus. But this is prevented by a small and very elastic cartilage, called epiglottis, which is attached only to the fore part of the larynx; so that the food in its passage to the oesophagus presses down this cartilage, which then covers the glottis or opening of the larynx; and at the same time the velum palati being capable of some degree of motion, is drawn backwards by its muscles, and closes the openings into the nose and the Eustachian tubes.—This, however, is not all. The larynx, which being composed of cartilaginous rings cannot fail in its ordinary state to compress the membranous canal of the oesophagus, is in the act of deglutition carried forwards and upwards by muscles destined for that purpose; and consequently drawing the fore part of the pharynx with it; that opening is fully dilated. When the aliment has reached the pharynx, its descent is promoted by its own proper weight, and by the muscular fibres of the oesophagus, which continue to contract from above downwards, until the aliment has reached the stomach. That these fibres have no inconsiderable share in deglutition, any person may experience, by swallowing with his head downwards, when the descent of the aliment cannot possibly be effected by its weight.

It is necessary that the nostrils and the lungs should communicate with the mouth, for the purposes of speech and respiration; but if the most minute part of our food happens to be introduced into the trachea, it never fails to produce a violent cough, and sometimes the most alarming symptoms. This is liable to happen when we laugh or speak in the act of deglutition; the food is then said to have passed the wrong way. And indeed this is not improperly expressed: for death would soon follow, if the quantity of aliment introduced into the trachea should be sufficient to obstruct the respiration only during a very short time; or if the irritating particles of food should not soon be thrown up again by means of the cough, which in these cases very seasonably increases in proportion to the degree of irritation.

If the velum palati did not close the passage to the nostrils, deglutition would be performed with difficulty, and perhaps not at all; for the aliment would return through the nose, as is sometimes the case in drinking. Children, from a deficiency in this velum palati, have been seen to die a few hours after birth; and they who from disease or any other causes have not this part perfect, swallow with difficulty.

The aliment, after having been sufficiently divided by the action of the teeth, and attenuated by the saliva, is received into the stomach, where it is destined to undergo a more considerable change.

The properties of the aliment not being much altered at its first entrance into the stomach, and before it is thoroughly blended with the gastric juice, it is capable of irritating the inner coat of the stomach to a certain degree, and occasions a contraction of its two orifices.—In this membranous bag, surrounded by the abdominal viscera, and with a certain degree of natural heat, the aliment undergoes a constant agitation by means of the abdominal muscles and of the diaphragm, and likewise by a certain contraction or expansion of the muscular fibres of the stomach itself. By this motion, every part of the food is exposed to the action of the gastric juice, which gradually divides and attenuates it, and prepares it for its passage into the intestines.

Some observations lately published by Mr Hunter, in the Philosophical Transactions, tend to throw considerable light on the principles of digestion. There are few dead bodies in which the stomach, at its great end, is not found to be in some degree digested (ii). Animals, or parts of animals, possessed of the living principle,

(h) The Abbé Spallanzani, who has written upon digestion, found, from a variety of experiments made upon quadrupeds, birds, and fishes, that digestion goes on for some time after death, though far less considerable than in living animals; but heat is necessary in many animals, or at least promotes it in a much greater degree. He found also, that when the stomach was cut out of the body, it had somewhat of the power of digestion, though this was trifling when compared with that which took place when the stomach was left in the body. In not one of the animals was the great curvature of the stomach dissolved, or much eroded after death. There was often a little erosion, especially in different fishes; in which, when he had cleared the stomach of its contents, the internal coat was wanting. In other animals there was only a slight excoriation; and the jury principle, when taken into the stomach, are not in the least affected by the action of that viscus; but the moment they lose the living principle, they become subject to its digestive powers. This seems to be the case with the stomach, which is enabled to resist the action of its juices in the living body: but when deprived of the living principle, it is then no longer able to resist the powers of that menstruum, which it had itself formed for the digestion of its contents; the process of digestion appearing to be continued after death. This is confirmed by what happens in the stomachs of fishes: They frequently swallow, without mastication, fish which are larger than the digesting parts of their stomach can contain; and in such cases, that part which is taken into the stomach, is more or less dissolved, while that part which remains in the esophagus is perfectly sound; and here, as well as in the human body, the digesting part of the stomach is often reduced to the same state as the digested part of the food. These appearances tend to prove, that digestion is not effected by a mechanical power, by contractions of the stomach, or by heat; but by a fluid secreted in the coats of the stomach, which is poured into its cavity, and there animalizes the food, or assimilates it to the nature of blood.

From some late experiments by M. Sage*, it appears, that inflammable air has the property of destroying and dissolving the animal texture: And as we swallow with the substances which serve us for food a great quantity of atmospherical air, M. Sage thinks it possible, that deploghisticated, which is its principle, may be converted in the stomach into inflammable air, or may modify into inflammable air a portion of the oily substance which is the principle of aliments. In this case, would not the inflammable air (he asks), by dissolving our food, facilitate its conversion into chyle?

Be this as it may, the food, after having remained one, two, or three hours in the stomach, is converted into a grayish pulp, which is usually called chymus, a word of Greek etymology, signifying juice, and some few milky or chylous particles begin to appear.—But the term of its residence in this bag is proportioned to the nature of the aliment, and to the state of the stomach and its juices. The thinner and more perfectly digested parts of the food pass by a little at a time into the duodenum, through the pylorus, the fibres of which relax to afford it a passage; and the grosser and less digested particles remain in the stomach, till they acquire a sufficient fluidity to pass into the intestines, where the nature of the chymus is perfectly changed. The bile and pancreatic juice which flow into the duodenum, and the mucus, which is everywhere distilled from the surface of the intestines, mix themselves with the alimentary palp, which they still further attenuate and dissolve, and into which they seem to infuse new properties.

Two matters very different from each other in their nature and destination, are the result of this combination.—One of these, which is composed of the liquid parts of the aliment, and of some of its more solid particles, extremely divided and mixed with the juices we have described, constitutes a very mild, sweet, and whitish fluid resembling milk, and distinguished by the name of chyle. This fluid is absorbed by the lacteal veins, which convey it into the circulation, where, by being assimilated into the nature of blood, it affords the supply of nutrition, which the continual waste of that body is found to require.—The other is the remains of the alimentary mass deprived of all its nutritious particles, and containing only such parts as were rejected by the absorbing mouths of the lacteals. This grosser part, called the feces, passes on through the course of the intestines, to be voided at the anus, as will be explained hereafter; for this process in the economy cannot be well understood till the motion of respiration has been explained. But the structure of the intestines is a subject which may be properly described in this place, and deserves to be attended to.

It has been already observed, that the intestinal canal is five or six times as long as the body, and that it forms many circumvolutions in the cavity of the abdomen, which it traverses from the right to the left, and again from the left to the right; in one place descending, and in another extending itself upwards. It was noticed likewise, that the inner coat of the intestines, by being more capacious than their exterior tunics, formed a multitude of plaits placed at a certain distance from each other, and called valvula conniventes. Now this disposition will be found to afford a farther proof of that divine wisdom, which the anatomist and physiologist cannot fail to discover in all their pursuits.—For if the intestinal canal was much shorter than it naturally is; if instead of the present circumvolution, it passed in a direct course from the stomach; and if its inner surface was smooth and destitute of valves; the aliment would consequently pass with great rapidity to the anus, and sufficient time would be wanting to assimilate the chyle, and for the necessary absorption of it into the lacteals; so that the body would be deprived of the supply of nutrition, which is so essential to life and health; but the length and circumvolutions of the intestines, the inequality of their internal surface, and the course of the aliment through them, all concur to perfect the separation of the chyle from the feces, and to afford the necessary nourishment to the body.

Sect. XIV. Of the Course of the Chyle, and of the Lymphatic System.

An infinite number of very minute vessels, called the lacteal veins, arise like net-work from the inner surface of the intestines (but principally from the jejunum and ileum), which are destined to imbibe the nutritious fluid or chyle. These vessels, which were discovered by Asellius in 1622 (1), pass obliquely through the coats of

(1) We are informed by Galen, that the lacteals had been seen in kids by Erasistratus, who considered them Of the intestine, and running along the mesentery, unite as they advance, and form larger branches, all of which pass through the mesenteric or conglomerate glands, which are very numerous in the human subject.

As they run between the intestines and these glands, they are styled *venae lacteae primi generis*; but after leaving these glands they are found to be less numerous, and being increased in size, are then called *venae lacteae secundi generis*, which go to deposit their contents in the thoracic duct, through which the chyle is conveyed into the blood.

The thoracic duct begins about the lower part of the first vertebra lumbarum, from whence it passes up by the side of the aorta, between that and the vena azygos, close to the vertebrae, being covered by the pleura. Sometimes it is found divided into two branches; but they usually unite again into one canal, which opens into the left subclavian vein, after having run a little way in an oblique course between its coats. The subclavian vein communicates with the vena cava, which passes to the right auricle of the heart.

The lower part of this duct being usually larger than any other part of it, has been named *receptaculum chyli*, or Pecquet's *receptacle*, in honour of the anatomist who first discovered it in 1651. In some quadrupeds, Heuson's in turtle and in fish, this enlargement is more considerable, in proportion to the size of the duct, than it usually is in the human subject, where it is not commonly found large enough to merit the name of receptaculum.

Opportunities of observing the lacteals in the human subject do not often occur; but they may be easily demonstrated in a dog or any other quadruped that is killed two or three hours after feeding upon milk, for then they appear filled with white chyle.

But these lacteals, which we have described as passing from the intestines through the mesentery to the thoracic duct, compose only a part of a system of vessels which perform the office of absorption, and which constitute, with their common trunk, the thoracic duct, and the conglomerate glands that are dispersed through the body, what may be styled the lymphatic abdominal system. So that what is said of the structure of one of these series of vessels may very properly be applied to that of the other.

The lymphatic veins (K) are minute pellucid tubes, lymphatics which, like the lacteals, direct their course towards the centre of the body, where they pour a colourless fluid into the thoracic duct. The lymphatics from all the lower parts of the body gradually unite as they approach this duct, into which they enter by three or four very large trunks, that seem to form the lower extremity of this canal, or *receptaculum chyli*, which may be considered as the great trunk of the lymphatic system. The lacteals open into it near the same place; and the lymphatics, from a large share of the upper parts of the body, pour their lymph into different parts of this duct as it runs upwards, to terminate in the left subclavian vein. The lymphatics from the right side of the neck, thorax, and right arm, &c., terminate in the right subclavian vein.

As the lymphatics commonly lie close to the large blood vessels, a ligature passed round the crural artery in a living animal, by enclosing the lymphatics, will occasion a distension of these vessels below the ligature, so as to demonstrate them with ease; and a ligature, passed round the thoracic duct, instantly after killing an animal, will, by stopping the course of its contents into the subclavian vein, distend not only the lacteals, but also the lymphatics in the abdomen and lower extremities, with their natural fluids (L).

The coats of these vessels are too thin to be separated from each other; but the mercury they are capable of sustaining, proves them to be very strong; and their great power of contraction, after undergoing considerable distension, together with the irritability with which Baron Haller found them to be endowed, seems to render it probable, that, like the blood-vessels, they have a muscular coat.

The lymphatics are nourished after the same manner as arteries carrying a milky fluid; but from the remote time in which he lived, they do not seem to have been noticed till they were discovered in a living dog by Asellius, who denominated them lacteals, and considered them as serving to convey the chyle from the intestines to the liver; for before the discovery of the thoracic duct, the use of the liver was universally supposed to be that of converting the chyle into blood. But the discovery of the thoracic duct by Pecquet, not long after, corrected this error. Pecquet very candidly confesses, that his discovery accidentally arose from his observing a white fluid, mixed with the blood, flowing out of the vena cava, after he had cut off the heart of a living dog; which he suspected to be chyle, and afterwards traced to its source from the thoracic duct: This duct had been seen near a hundred years before in a horse by Enstachius, who speaks of it as a vein of a particular structure, but without knowing anything of its termination or use.

(K) The arteries in their course through the body becoming gradually too minute to admit the red globules of the blood, have then been styled capillary or lymphatic arteries. The vessels which are here described as constituting the lymphatic system, were at first supposed to be continued from those arteries, and to convey back the lymph, either into the red veins or the thoracic duct; the office of absorption having been attributed to the red veins. But we know that the lymphatic veins are not continuations of the lymphatic arteries, but that they constitute the absorbent system. There are still, however, some very respectable names among the anatomists of the present age, who contend, that the red veins act likewise as absorbers; but it seems to have been clearly proved, that the red veins do absorb nowhere but in the cavernous cells of the penis, the erection of which is occasioned by a distension of these cells with arterial blood.

(L) In the dead body they may be easily demonstrated by opening the artery ramifying through any viscus, as in the spleen, for instance, and then throwing in air; by which the lymphatics will be distended. One of them may then be punctured, and mercury introduced into it through a blowpipe. as all the other parts of the body. For even the most minute of these vessels are probably supplied with still more minute arteries and veins. This seems to be proved by the inflammation of which they are susceptible; and the painful swellings which sometimes take place in lymphatic vessels prove that they have nerves as well as blood-vessels.

Both the lacteals, lymphatics, and thoracic duct, are furnished with valves, which are much more common in these vessels than in the red veins. These valves are usually in pairs, and serve to promote the course of the chyle and lymph towards the thoracic duct, and to prevent its return. Mention has been made of the glands, through which the lacteals pass in their course through the mesentery; and it is to be observed, that the lymphatics pass through similar glands in their way to the thoracic duct. These glands are all of the conglobate kind, but the changes which the chyle and lymph undergo in their passage through them, have not yet been ascertained.

The lymphatic vessels begin from surfaces and cavities in all parts of the body as absorbents. This is a fact now universally allowed; but how the fluids as they absorb are poured into these cavities, is a subject of controversy. The contents of the abdomen, for instance, were described as being constantly moistened by a very thin watery fluid. The same thing takes place in the pericardium, pleura, and all the other cavities of the body, and this watery fluid is the lymph. But whether it is exhaled into those cavities through the minute ends of arteries, or transuded through their coats, are the points in dispute. We cannot here be permitted to relate the many ingenious arguments that have been advanced in favour of each of these opinions; nor is it perhaps of consequence to our present purpose to enter into the dispute. It will be sufficient if the reader can form an idea of what the lymph is, and of the manner in which it is absorbed.

The lymph, from its transparency and want of colour, would seem to be nothing but water; and hence the first discoverers of these vessels styled them ductus aquosi: but experiments prove, that the lymph of a healthy animal coagulates by being exposed to the air or a certain degree of heat, and likewise by being suffered to rest: seeming to agree in this property with that part of the blood called the coagulable lymph.—This property of the lymph leads to determine its use, in moistening and lubricating the several cavities of the body in which it is found; and for which, by its gelatinous principle, it seems to be much better calculated than a pure and watery fluid would be, for such it has been supposed to be by some anatomists.

The mouths of the lymphatics and lacteals, by acting as capillary tubes, seem to absorb the lymph and chyle somewhat in the same manner as a capillary tube of glass, when put into a basin of water, is enabled to attract the water into it to a certain height: but it is probable that they likewise possess a living power, which assists in performing this office. In the human body the lymph, or the chyle, is probably conveyed upon this principle as far as the first pair of valves, which seem to be placed not far from the orifice of the absorbing vessel, whether lymphatic or lacteal; and the fluid will then be propelled forwards, by a continuation of the absorption at the orifice. But this does not seem to be the only inducement to its progress towards the thoracic duct; these vessels have probably a muscular coat, which may serve to press the fluid forwards from one pair of valves to another; and as the large lymphatic vessels and the thoracic duct are placed close to the large arteries, which have a considerable pulsation, it is reasonable to suppose, that they derive some advantages from this situation.

Sect. XV. Of the Generative Organs; of Conception, &c.

§ 1. The Male Organs.

The male organs of generation have been usually divided into the parts which serve to prepare the semen from the blood, and those which are destined to convey it into the womb. But it seems to be more proper to distinguish them into the preparing, the containing, and the expelling parts, which are the different offices of the testes, the vesiculae seminales, and the penis; and this is the order in which we propose to describe them.

The testes are two glandular bodies, serving to secrete the semen from the blood. They are originally formed and lodged within the cavity of the abdomen; and it is not till after the child is born, or very near that time, that they begin to pass into the groin, and from thence into the scrotum (m). By this disposition they are very wisely protected from the injuries to which they would be liable to be exposed, from the different positions of the child at the time of parturition.

The testicles in this state are loosely attached to the psoas muscles, by means of the peritoneum by which they are covered; and they are at this time of life connected in a very particular manner to the parietes of the abdomen, and likewise to the scrotum, by means of a substance which Mr Hunter calls the ligament or gubernaculum testis, because it connects the testis with the scrotum.

(m) It sometimes happens in dissecting ruptures, that the intestine is found in the same sac, and in contact with the testis. This appearance was at first attributed to a supposed laceration of the peritoneum; but later observations, by pointing out the situation of the testicles in the fetus, have led to prove, that the testis, as it descends into the scrotum, carries with it a portion or elongation of the peritoneum, which becomes its tunica vaginalis, or a kind of sac, in which the testicle is lodged, as will be explained in the course of this section. The communication between this sac and the cavity of the abdomen is usually soon cut off; but in some subjects it continues open during life; and when a hernia or descent of the intestine takes place in such a subject, it does not push down a portion of the peritoneum before it, as it must otherwise necessarily do, but passes at once through this opening, and comes in contact with the naked testicle, constituting that particular species of rupture called hernia congenita. scrotum, and directs its course in its descent. This gubernaculum is of a pyramidal form, with its bulbous head fixed to the lower end of the testes and epidydimis, and loses its lower and slender extremity in the cellular membrane of the scrotum. It is difficult to ascertain what the structure and composition of this gubernaculum is, but it is certainly vascular and fibrous; and from certain circumstances, it would seem to be in part composed of the cremaster muscle, running upwards to join the lower end of the testis.

We are not to suppose that the testicle, when descended into the scrotum, is to be seen loose as a piece of gut or omentum would be in a common hernial sac. We have already observed, that during its residence in the cavity of the abdomen it is attached to the peritoneum, which descends with it; so that when the sac is completed in the scrotum, the testicle is at first attached only to the posterior part of it, while the fore part of it lies loose, and for some time affords a communication with the abdomen. The spermatic chord, which is made up of the spermatic artery and vein, and of the vas deferens or excretory duct of the testis, is closely attached behind to the posterior part of this elongation of the peritoneum. But the fore part of the peritoneal sac, which is at first loose and not attached to the testicle, closes after a certain time, and becomes united to the posterior part, and thus perfectly surrounds the testicle as it were in a purse.

The testicles of the fetus differ only in their size and situation from those of the adult. In their passage from the abdomen they descend through the abdominal rings into the scrotum, where they are supported and defended by various integuments.

What the immediate cause of this descent is, has not yet been satisfactorily determined. It has been ascribed to the effects of respiration, but the testicles have sometimes been found in the scrotum before the child has breathed; and it does not seem to be occasioned by the action of the cremaster muscle, because the same effect would be liable to happen in the hedgehog and some other quadrupeds, whose testicles remain in the abdomen during life.

The scrotum, which is the external or common covering of both testicles, is a kind of sac formed by the common integuments, and externally divided into two equal parts by a prominent line called raphe.

In the inner part of the scrotum we meet with a cellular coat called dartos (n), which by its duplicature divides the scrotum into two equal parts, and forms what is called septum scroti, which corresponds with the raphe. The collapse which is so often observed to take place in the scrotum of the healthy subject, when excited by cold or by the stimulus of venery, seems to be very properly attributed to the contractile motion of the skin, and not to any muscular fibres, as is the case in dogs and some other quadrupeds.

The scrotum, then, by means of its septum, is found to make two distinct bags, in which the testicles, invested by their proper tunics, are securely lodged and separated from each other. These coats are the cremaster, the tunica vaginalis, and the tunica albuginea. The first of these is composed of muscular fibres, and is to be considered only as a partial covering of the testis; for it surrounds only the spermatic chord, and terminates upon the upper and external parts of the tunica vaginalis testis, serving to draw up and suspend the testicle (o). The tunica vaginalis testis has already been described as being a thin production of the peritoneum loosely adhering everywhere to the testicle, which it includes as it were in a bag. The tunica albuginea is a firm, white, and very compact membrane of a glistening appearance, which immediately invests the body of the testis and the epididymis; serving in some measure to connect them to each other, but without extending itself at all to the spermatic chord. This tunica albuginea serves to confine the growth of the testis and epididymis within certain limits, and by giving them a due degree of firmness, enables them to perform their proper functions.

Having removed this last tunic, we discover the substance of the testicle itself, which appears to be made up of an infinite number of very elastic filaments, which may be best distinguished after macerating the testicle in water. Each testicle is made up of the spermatic artery and vein, and the excretory vessels or tubuli seminiferi. There are likewise a great number of absorbent vessels, and some branches of nerves to be met with in the testicles.

The spermatic arteries arise one on each side from the aorta, generally about an inch below the emulgents. The right spermatic vein commonly passes into the vena cava; but the left spermatic vein usually empties itself into the emulgent on that side; and it is supposed to take this course into the emulgent, that it may avoid passing over the aorta, which it would be obliged to do in its way to the vena cava.

The blood is circulated very slowly through the spermatic artery, which makes an infinite number of convolutions in the substance of the testicle, where it deposits the semen, which passes through the tubuli seminiferi. These tubuli seminiferi are seen running in short waves from the tunica albuginea to the axis of the testicle; and are divided into distinct portions by certain thin membranous productions, which originate from the tunica albuginea. They at length unite, and by an infinite number of convolutions form a sort of appendix to the testis called epididymis (p), which is

(n) The dartos has usually been considered as a muscle, and is described as such both by Douglas and Winslow. But there being no part of the scrotum of the human subject which can be said to consist of muscular fibres, Albinius and Haller have very properly omitted to describe the dartos as a muscle, and consider it merely as a cellular coat.

(o) The cremaster muscle is composed of a few fibres from the obliquus internus abdominis, which uniting with a few from the transversalis, descend upon the spermatic chord, and are insensibly lost upon the tunica vaginalis of the testicle. It serves to suspend and draw up the testicle.

(p) The testicles were named didymi by the ancients; and the name of this part was given to it on account of its situation upon the testicle. A vascular body of an oblong shape, situated upon the superior part of each testicle. These tubuli of the epididymis at length form an excretory duct called vas deferens, which ascends towards the abdominal rings, with the other parts that make up the spermatic chord, and then a separation takes place; the nerves and blood-vessels passing on to their several terminations, and the vas deferens going to deposit its semen in the vesiculae seminales, which are two soft bodies of a white and convoluted appearance externally, situated obliquely between the rectum and the lower part of the bladder, and uniting together at the lower extremity. From these reservoirs (a), which are plentifully supplied with blood-vessels and nerves, the semen is occasionally discharged through two short passages, which open into the urethra close to a little eminence called verumontanum.

Near this eminence we meet with the prostate, which is situated at the neck of the bladder, and is described as being of a glandular structure. It is shaped somewhat like a heart with its small end foremost, and invests the origin of the urethra. Internally it appears to be of a firm substance, and composed of several follicles, secreting a whitish viscid fluid, that is discharged by ten or twelve excretory ducts into the abdomen, urethra, on each side of the openings of the vesiculae seminales, at the same time, and from the same causes, that the semen is expelled. As this latter fluid is found to be exceedingly limpid in the vesiculae seminales of the dead subject, it probably owes its whiteness and viscosity to this liquor of the prostate.

The penis, which is to be considered as the vehicle or active organ of procreation, is composed of two columns, the corpora cavernosa, and corpus spongiosum. The corpora cavernosa, which constitute the greatest part of the penis, may be described as two cylindrical ligamentous tubes, each of which is composed of an infinite number of minute cells of a spongy texture, which communicate with each other. These two bodies are of a very pliant texture, and capable of considerable distension; and being united laterally to each other, occasion by this union a space above and another below. The uppermost of these spaces is filled by the blood-vessels, and the lower one, which is larger than the other, by the urethra and its corpus spongiosum. These two cavernous bodies are at first only separated.

(a) That the bags called vesiculae seminales, are reservoirs of semen, is a circumstance which has been by anatomists universally believed. Mr J. Hunter, however, from several circumstances, has been induced to think this opinion erroneous.

He has examined these vesiculae in people who have died suddenly, and he found their contents to be different in their properties from the semen. In those who had lost one of the testicles, or the use of one of them, by disease, both the vesiculae were full, and their contents similar. And in a luxus naturae, where there was no communication between the vasa deferentia and vesiculae, nor between the vesiculae and penis, the same thing took place.

From these observations, he thinks we have a presumptive proof, That the semen can be absorbed in the body of the testicle and the epididymis, and that the vesicula secrete a mucus which they are capable of absorbing when it cannot be made use of; that the semen is not retained in reservoirs after it is secreted, and kept there till it is used; but that it is secreted at the time in consequence of certain affections of the mind stimulating the testicles to this action.

He corroborates his observations by the appearance on dissection in other animals; and here he finds, That the shape and contents of the vesicula vary much in different animals, while the semen in most of them he has examined is nearly the same: That the vasa deferentia in many animals do not communicate with the vesiculae; That the contents of the vesiculae of castrated and perfect animals are similar, and nearly equal in quantity, in no way resembling the semen as emitted from the animal in coitu, or what is found in the vas deferens after death. He observes likewise, that the bulb of the urethra of perfect males is considerably larger than in castrated animals.

From the whole, he thinks the following inferences may be fairly drawn: That the bags called vesiculae seminales are not seminal reservoirs, but glands secreting a peculiar mucus: and that the bulb of the urethra is properly speaking the receptacle of the semen, in which it is accumulated previous to ejection.

But although he has endeavoured to prove that the vesiculae do not contain the semen, he has not been able to ascertain their particular use. He thinks, however, we may be allowed upon the whole to conclude, that they are, together with other parts, subservient to the purposes of generation.

Although the author has treated this subject very ably, and made many ingenious observations, some things may be objected to what he has advanced; of which the following are a few: That those animals who have bags called vesiculae seminales perform copulation quickly; whereas others that want them, as the dog kind, are tedious in copulation: That in the human body, at least, there is a free communication between the vasa deferentia and vesiculae; and in animals where the author has observed no communication between the vasa deferentia and vesiculae, there may be a communication by vessels not yet discovered, and which may be compared to the hepato-cystic ducts in fowls and fishes: That the fluid in the end of the vasa deferentia and the vesiculae seminales are similar, according to the author's own observation: That the vesiculae in some animals increase and decrease with the testicle at particular seasons: That in birds and certain fishes, there is a dilatation of the ends of the vasa deferentia, which the author himself allows to be a reservoir for the semen.

With respect to the circumstance of the bulb of the urethra answering the purpose of a reservoir, the author has mentioned no facts which tend to establish this opinion. See Observations on certain Parts of the Animal Economy. The arteries of the penis are chiefly derived from the internal iliacs. Some of them are supposed to terminate by pubic orifices within the corpora cavernosa and corpus spongiosum; and others terminate in veins, which at last make up the vena magna dorsi penis, and other smaller veins, which are in general distributed in like order with the arteries.

Its nerves are large and numerous. They arise from the great sciatic nerve, and accompany the arteries in their course through the penis.

We have now described the anatomy of this organ; and there only remains to be explained, how it is enabled to attain that degree of firmness and distension which is essential to the great work of generation.

The greatest part of the penis has been spoken of as being of a spongy and cellular texture, plentifully supplied with blood vessels and nerves, and as having muscles to move it in different directions. Now, the blood is constantly passing into its cells through the small branches of the arteries which open into them, and is from thence as constantly returned by the veins, so long as the corpora cavernosa and corpus spongiosum continue to be in a relaxed and pliant state. But when, from any nervous influence, or other means which it is not necessary here to define or explain, the erectores penis, ejaculatores seminis, levatores ani, &c., are induced to contract, the veins undergo a certain degree of compression, and the passage of the blood through them is so much impeded, that it collects in them in a greater proportion than they are enabled to carry off, so that the penis gradually enlarges, and being more and more forcibly drawn up against the os pubis, the vena magna itself is at length compressed, and the penis becomes fully distended. But as the causes which first occasioned this distension subside, the penis gradually returns to its state of relaxation.

§ 2. Female Organs of Generation.

Anatomical writers usually divide the female organs of generation into external and internal. In the first division they include the mons veneris, labia pudendi, perineum, clitoris, nymphæ, and carunculae myrtiformes; and in the latter, the vagina, with the uterus and its appendages.

The mons veneris, which is placed on the upper part of the symphysis pubis, is internally composed of adipose membranes, which makes it soft and prominent; it divides into two parts called labia pudendi, which descending towards the rectum, from which they are divided by the perineum, form what is called the fourchette. The perineum is that fleshy space which extends about an inch and a half from the fourchette to the anus, and from thence about two inches to the coccyx.

The labia pudendi being separated, we observe a sulcus called fossa magna; in the upper part of which is placed the clitoris, a small round spongy body, in some measure resembling the male penis, but impervious, composed of two corpora cavernosa, arising from the tuberosities of the ossa ischii; furnished with two pair

(R.) Both Heister and Morgagni observe, that they have sometimes not been able to find these glands; so that they do not seem to exist in all subjects. of muscles, the erectores clitoridis, and the sphincter or constrictor ostii vaginae; and terminating in the glans, which is covered with its prepuce. From the lower part, on each side of the fossa, pass the nymphae, two membranous and spongy folds, which seem destined for useful purposes in parturition, by tending to enlarge the volume of the vagina as the child's head passes through it. Between these, about the middle of the fossa magna, we perceive the orifice of the vagina or os externum, closed by folds and wrinkles; and about half an inch above this, and about an inch below the clitoris, appears the meatus urinarius or orifice of the urethra, much shorter, though somewhat larger, than in men, with a little prominence at its lower edge, which facilitates the introduction of the catheter.

The os externum is surrounded internally by several membranous folds called carunculae myrtiformes, which are partly the remains of a thin membrane called hymen, that covers the vagina in children. In general the hymen is sufficiently open to admit the passage of the menses, if it exists at the time of their appearance; sometimes, however, it has been found perfectly closed.

The vagina, situated between the urethra and the rectum, is a membranous cavity, surrounded, especially at its external extremity, with a spongy and vascular substance, which is covered by the sphincter ostii vaginae. It terminates in the uterus, about half an inch above the os tineum, and is wider and shorter in women who have had children than in virgins.

All these parts are plentifully supplied with blood vessels and nerves. Around the nymphae there are sebaceous follicles, which pour out a fluid to lubricate the inner surface of the vagina; and the meatus urinarius, like the urethra in the male subject, is constantly moistened by a mucus, which defends it against the acrimony of the urine.

The uterus is a hollow viscus, situated in the hypogastric region, between the rectum and bladder. It is destined to receive the first rudiments of the fetus, and to assist in the development of all its parts, till it arrives at a state of perfection, and is fitted to enter into the world, at the time appointed by the wise Author of nature.

The uterus, in its unimpregnated state, resembles a pear in shape, somewhat flattened, with its fundus or bottom part turned towards the abdomen, and its cervix or neck surrounded by the vagina. The entrance into its cavity forms a little protuberance, which has been compared to the mouth of a tench, and is therefore called os tineum.

The substance of the uterus, which is of a considerable thickness, appears to be composed of muscular and small ligamentous fibres, small branches of nerves, some lymphatics, and with arteries and veins innumerable. Its nerves are chiefly derived from the intercostal, and its arteries and veins from the hypogastric and spermatic. The membrane which lines its cervix is a continuation of the inner membrane of the vagina; but the outer surface of the body of the uterus is covered with the peritoneum, which is reflected over it, and descends from thence to the intestinum rectum. This duplicature of the peritoneum, by passing off from the sides of the uterus to the sides of the pelvis, is there firmly connected, and forms what are called ligamenta uteri lata; which not only serve to support the uterus, but to convey nerves and blood vessels to it.

The ligamenta uteri rotunda arise from the sides of the fundus uteri, and passing along within the fore part of the ligamenta lata, descend through the abdominal rings, and terminate in the substance of the mons veneris. The substance of these ligaments is vascular; and although both they and the ligamenta lata admit the uterus, in the virgin state, to move only about an inch up and down, yet in the course of pregnancy they admit of considerable distension, and after parturition return nearly to their original state with surprising quickness.

On each side of the inner surface of the uterus, in the angle near the fundus, a small orifice is to be discovered, which is the beginning of one of the tubae Fallopianae. Each of these tubes, which are two in number, passing through the substance of the uterus, is extended along the broad ligaments, till it reaches the edge of the pelvis, from whence it reflects back; and turning over behind the ligaments, about an inch of its extremity is seen hanging loose in the pelvis, near the ovarium. These extremities, having a jagged appearance, are called fimbriae, or morusa diaboli. Each tuba Fallopiana is usually about three or four inches long. Their cavities are at first very small, but become gradually larger, like a trumpet, as they approach the fimbriae.

Near the fimbriae of each tuba Fallopiana, about an inch from the uterus, is situated an oval body called ovarium, of about half the size of the male testicle. Each of these ovaria is covered by a production of the peritoneum, and hangs loose in the pelvis. They are of a flat and angular form, and appear to be composed of a white and cellular substance, in which we are able to discover several minute vesicles filled with a coagulable lymph, of an uncertain number, commonly exceeding 12 in each ovary. In the female of riper years, these vesicles become exceedingly turgid, and a kind of yellow coagulum is gradually formed within one of them, which increases for a certain time. In conception, one of these mature ova is supposed to be impregnated with the male semen, and to be squeezed out of its nidus into the Fallopian tube; after which the ruptured part forms a substance which in some animals is of a yellow colour, and is therefore called corpus luteum; and it is observable, that the number of these scars or fissures in the ovarium, constantly corresponds with the number of fetuses excluded by the mother.

§ 3. Of Conception.

Man, being ever curious and inquisitive, has naturally been led to inquire after the origin of his existence; and the subject of generation has employed the philosophical world in all ages: but in following nature up to her minute recesses, the philosopher soon finds himself bewildered; and his imagination often supplies that which he so eagerly wishes to discover, but which is destined perhaps never to be revealed to him. Of the many theories which have been formed on this subject, that of the ancient philosophers seems to have been the most simple; they considered the male semen as alone capable of forming the fetus, and believed believed that the female only afforded it a lodging in the womb, and supplied it with nourishment after it was perfectly formed. This opinion, however, soon gave place to another, in which the female was allowed a more considerable share in conception.

This second system considered the fetus as being formed by the mixture of the seminal liquor of both sexes, by a certain arrangement of its several particles in the uterus. But in the 16th century, vesicles or eggs were discovered in the ovaria or female testicles; the fetus had been found sometimes in the abdomen, and sometimes in the Fallopian tubes; and the two former opinions were exploded in favour of a new doctrine. The ovaria were compared to a bunch of grapes, being supposed to consist of vesicles, each of which had a stalk; so that it might be disengaged without hurting the rest, or spilling the liquor it contained. Each vesicle was said to include a little animal, almost complete in all its parts; and the vapour of the male semen being conveyed to the ovarium, was supposed to produce a fermentation in the vesicle which approached the nearest to maturity; and thus inducing it to disengage itself from the ovarium, it passed into the tuba Fallopiana, through which it was conveyed to the uterus. Here it was supposed to take root like a vegetable seed, and to form with the vessels originating from the uterus, what is called the placenta; by means of which the circulation is carried on between the mother and the fetus.

This opinion, with all its absurdities, continued to be almost universally adopted till the close of the same century, when Leeuwenhoek, by means of his glasses, discovered certain opaque particles, which he described as so many animalcula, floating in the seminal fluid of the male.

This discovery introduced a new schism among the philosophers of that time, and gave rise to a system which is not yet entirely exploded. According to this theory, the male semen passing into the tuba Fallopiana, one of the animalcula penetrates into the substance of the ovarium, and enters into one of its vesicles or ova. This impregnated ovum is then squeezed from its husk, through the coats of the ovarium, and being seized by the fimbria, is conducted through the tube to the uterus, where it is nourished till it arrives at a state of perfection. In this system there is much ingenuity; but there are certain circumstances supposed to take place, which have been hitherto inexplicable. A celebrated modern writer, M. Buffon, endeavours to restore, in some measure, the most ancient opinion, by allowing the female semen a share in this office; asserting, that the animalcula or organic particles are to be discovered in the seminal liquor of both sexes; he derives the female semen from the ovaria, and he contends that no ovum exists in those parts. But in this idea he is evidently mistaken; and the opinion now most generally adopted is, that an impregnation of the ovum, by the influence of the male semen, is essential to conception. That the ovum is to be impregnated, there can be no doubt; but as the manner in which such an impregnation is supposed to take place, and the means by which the ovum afterwards gets into the Fallopian tube, and from thence into the uterus, are still founded chiefly on hypothesis, we will not attempt to extend farther the investigation of a subject concerning which so little can be advanced with certainty.

§ 4. Of the Fetus in Utero.

Opportunities of dissecting the human gravid uterus occurring but seldom, the state of the embryo (s) immediately after conception cannot be perfectly known.

When the ovum descends into the uterus, it is supposed to be very minute; and it is not till a considerable time after conception that the rudiments of the embryo begin to be ascertained.

About the third or fourth week the eye may discover the first lineaments of the fetus; but these lineaments are as yet very imperfect, it being only about the size of a house fly. Two little vesicles appear in an almost transparent jelly; the largest of which is destined to become the head of the fetus, and the other smaller one is reserved for the trunk. But at this period no extremities are to be seen; the umbilical cord appears only as a very minute thread, and the placenta does not as yet absorb the red particles of the blood. At six weeks, not only the head, but the features of the face, begin to be developed. The nose appears like a small prominent line, and we are able to discover another line under it, which is destined for the separation of the lips. Two black points appear in the place of eyes, and two minute holes mark the ears. At the sides of the trunk, both above and below, we see four minute protuberances, which are the rudiments of the arms and legs. At the end of eight weeks the body of the fetus is upwards of an inch in length, and both the hands and feet are to be distinguished. The upper extremities are found to increase faster than the lower ones, and the separation of the fingers is accomplished sooner than that of the toes.

At this period the human form may be decisively ascertained: all the parts of the face may be distinguished, the shape of the body is clearly marked out, the haunches and the abdomen are elevated, the fingers and toes are separated from each other, and the intestines appear like minute threads.

At the end of the third month, the fetus measures about three inches; at the end of the fourth month, five inches; in the fifth month, six or seven inches; in the sixth month, eight or nine inches; in the seventh month, eleven or twelve inches; in the eighth month, fourteen or fifteen inches; and at the end of the ninth month, or full time, from eighteen to twenty-two inches. But as we have not an opportunity of examining the same fetus at different periods of pregnancy, and as their size and length may be influenced by the constitution and mode of life of the mother, calculations of this kind must be very uncertain.

The fetus during all this time assumes an oval figure,

(s) The rudiments of the child are usually distinguished by this name till the human figure can be distinctly ascertained, and then it has the appellation of fetus. The capacity of the uterus increases in proportion to the growth of the fetus, but without becoming thinner in its substance, as might naturally be expected. The nourishment of the fetus, during all this time, seems to be derived from the placenta, which appears to be originally formed by that part of the ovum which is next the fundus uteri. The remaining part of the ovum is covered by a membrane called spongy chorion (τ); within which is another called true chorion, which includes a third termed amnios (υ): this contains a watery fluid, which is the liquor amnii (ν), in which the fetus floats till the time of its birth. On the side next the fetus, the placenta is covered by the amnios and true chorion; on the side next the mother it has a production continued from the spongy chorion. The amnios and chorion are remarkably thin and transparent, having no blood vessels entering into their composition. The spongy chorion is opaque and vascular.

In the first months of pregnancy, the involucre bear a large proportion to their contents; but this proportion is afterwards reversed, as the fetus increases in bulk.

The placenta, which is the medium through which the blood is conveyed from the mother to the fetus, and the manner in which this conveyance takes place, deserve next to be considered.

The placenta is a broad, fat, and spongy substance, like a cake, closely adhering to the inner surface of the womb, usually near the fundus, and appearing to be chiefly made up of the ramifications of the umbilical arteries and vein, and partly of the extremities of the uterine vessels. The arteries of the uterus discharge their contents into the substance of this cake; and the veins of the placenta, receiving the blood either by a direct communication of vessels, or by absorption, at length form the umbilical vein, which passes on to the sinus of the vena portae, and from thence to the vena cava, by means of the canalis venosus, a communication that is closed in the adult. But the circulation of the blood through the heart is not conducted in the fetus as in the adult; in the latter, the blood is carried from the right auricle of the heart through the pulmonary artery, and is returned to the left auricle by the pulmonary vein; but a dilatation of the lungs is essential to the passage of the blood through the pulmonary vessels, and this dilatation cannot take place till after the child is born and has respired. This deficiency, however, is supplied in the fetus by an immediate communication between the right and left auricle, through an oval opening, in the septum which divides the two auricles, called foramen ovale. The blood is likewise transmitted from the pulmonary artery to the aorta, by means of a duct called canalis arteriosus, which, like the canalis venosus, and foramen ovale, gradually closes after birth.

The blood is returned again from the fetus through two arteries, called the umbilical arteries, which arise from the iliacs. Those two vessels taking a winding course with the vein, form with that, and the membranes by which they are surrounded, what is called the umbilical chord. These arteries, after ramifying through the substance of the placenta, discharge their blood into the veins of the uterus; in the same manner as the uterine arteries discharged their blood into the branches of the umbilical vein. So that the blood is constantly passing in at one side of the placenta and out at the other; but in what particular manner it gets through the placenta is a point not yet determined.

EXPLANATION

(τ) Dr Hunter has described this as a lamella from the inner surface of the uterus. In the latter months of pregnancy it becomes gradually thinner and more connected with the chorion: he has named it membrana caducua, or decidua, as it is cast off with the placenta. Signior Scarpa, with more probability, considers it as being composed of an inspissated coagulable lymph.

(υ) In some quadrupeds, the urine appears to be conveyed from the bladder through a canal called urachus to the allantois, which is a reservoir, resembling a long and blind gut, situated between the chorion and amnios. The human fetus seems to have no such reservoir, though some writers have supposed that it does exist. From the top of the bladder a few longitudinal fibres are extended to the umbilical chord; and these fibres have been considered as the urachus, though without having been ever found pervious.

(ν) The liquor amnii coagulates like the lymph. It has been supposed to pass into the oesophagus, and to afford nourishment to the fetus; but this does not seem probable. Children have come into the world without an oesophagus, or any communication between the stomach and the mouth; but there has been no well attested instance of a child's having been born without a placenta; and it does not seem likely, that any of the fluid can be absorbed through the pores of the skin, the skin in the fetus being everywhere covered with a great quantity of mucus. EXPLANATION OF PLATES XXVII. XXVIII. AND XXIX.

PLATE XXVII.

Fig. 1. Shows the Contents of the Thorax and Abdomen in situ.

1. Top of the trachea or windpipe. 2. The internal jugular veins. 3. The subclavian veins. 4. The vena cava descendens. 5. The right auricle of the heart. 6. The right ventricle. 7. Part of the left ventricle. 8. The aorta descendens. 9. The pulmonary artery. 10. The right lung, part of which is cut off to show the great blood-vessels. 11. The left lung entire. 12. The anterior edge of the diaphragm. 13. The two great lobes of the liver. 14. The ligamentum rotundum. 15. The gall-bladder. 16. The stomach. 17. The jejunum and ilium. 18. The spleen.

Fig. 2. Shows the Organs subservient to the Chylopoietic Viscera,—with those of Urine and Generation.

1. The under side of the two great lobes of the liver. 2. Lobulus Spigellii. 3. The ligamentum rotundum. 4. The gall-bladder. 5. The pancreas. 6. The spleen. 7. The kidneys. 8. The aorta descendens. 9. Vena cava ascendens. 10. The renal veins covering the arteries. 11. A probe under the spermatic vessels and a bit of the inferior mesenteric artery, and over the ureters. 12. The ureters. 13. The iliac arteries and veins. 14. The rectum intestinum. 15. The bladder of urine.

Fig. 3. Shows the Chylopoietic Viscera, and Organs subservient to them, taken out of the Body entire.

A. The under side of the two great lobes of the liver. B. Ligamentum rotundum. C. The gall-bladder. D. Ductus cysticus. E. Ductus hepaticus. F. Ductus communis choledochus. G. Vena portarum. H. Arteria hepatica. I. The stomach. KK. Vena et arteriae gastro-epiploicae, dextra et sinistra. LL. Vena et arteriae coronariae ventriculi. M. The spleen. NN. Mesocolon, with its vessels. OOO. Intestinum colon. P. One of the ligaments of the colon, which is a bundle of longitudinal muscular fibres. QQQQ. Jejunum and ilium. RR. Sigmoid flexure of the colon with the ligament continued, and over S, the rectum intestinum. TT. Levatores ani. U. Sphincter ani. V. The place to which the prostate gland is connected. W. The anus.

Fig. 4. Shows the heart of a Fetus at the full time, with the Right Auricle cut open to show the Foramen Ovale, or passage between both Auricles.

a. The right ventricle. b. The left ventricle. cc. The outer side of the right auricle stretched out. dd. The posterior side, which forms the anterior side of the septum. e. The foramen ovale, with the membrane or valve which covers the left side. f. Vena cava inferior passing through g, a portion of the diaphragm.

Fig. 5. Shows the Heart and Large Vessels of a Fetus at the full time.

a. The left ventricle. b. The right ventricle. c. A part of the right auricle. d. Left auricle. ee. The right branch of the pulmonary artery. f. Arteria pulmonalis. gg. The left branch of the pulmonary artery, with a number of its largest branches dissected from the lungs. h. The canalis arteriosus. i. The arch of the aorta. kk. The aorta descendens. l. The left subclavian artery. m. The left carotid artery. n. The right carotid artery. o. The right subclavian artery. p. The origin of the right carotid and right subclavian arteries in one common trunk. q. The vena cava superior or descendens. r. The right common subclavian vein. s. The left common subclavian vein.

N. B.—All the parts described in this figure are to be found in the adult, except the canalis arteriosus.

PLATE XXVIII.

Fig. 1. Exhibits the more superficial Lymphatic Vessels of the Lower Extremity.

A. The spine of the os ilium. B. The os pubis. C. The iliac artery. D. The knee. EEEF. Branches of the crural artery. G. The musculus gastrocnemius. H. The tibia. I. The tendon of the musculus tibialis anticus. On the outlines, a, A lymphatic vessel belonging to the top of the foot. B, Its first division into branches. c, c, c, Other divisions of the same lymphatic vessel. d, A small lymphatic gland. e, The lymphatic vessels which lie between the skin and the muscles of the thigh. ff, Two lymphatic glands at the upper part of the thigh below the groin. gg, Other glands. h, A lymphatic vessel which passes by the side of those glands without communicating with them; and, bending towards the inside of the groin at (i), opens into the lymphatic gland (k). ll, Lymphatic glands in the groin, which are common to the lymphatic vessels of the genitals and those of the lower extremity. m, n, A plexus of lymphatic vessels passing on the inside of the iliac artery.

Fig. 2. Exhibits a Back View of the Lower Extremity, dissected so as to show the deeper-seated Lymphatic Vessels which accompany the Arteries.

A. The os pubis. B. The tuberosity of the ischium. C. That part of the os ilium which was articulated with the os sacrum. D. The extremity of the iliac artery appearing above the groin. E. The knee. F, F. The two cut surfaces of the triceps muscle, which was divided to show the lymphatic vessels that pass through its perforation along with the crural artery. G. The edge of the musculus gracilis. H. The gastrocnemius and soleus, much shrunk by being dried, and by the soleus being separated from the tibia to expose the vessels. I. The heel. K. The sole of the foot. L. The superficial lymphatic vessels passing over the knee, to get to the thigh. On the outlines; Plate XXIX.

Fig. 1. Represents the Under and Posterior Side of the Bladder of Urine, &c.

a, The bladder. bb, The insertion of the ureters. cc, The vasa deferentia, which convey the semen from the testicles to dd, The vesiculae seminales—and pass through e, The prostate gland, to discharge themselves into f, The beginning of the urethra.

Fig. 2. A transverse Section of the Penis.

gg, Corpora cavernosa penis. h, Corpus cavernosum urethrae. i, Urethra. k, Septum penis. ll, The septum between the corpus cavernosum urethrae and that of the penis.

Fig. 3. A longitudinal Section of the Penis.

mm, The corpora cavernosa penis divided by o, The septum penis. n, The corpus cavernosum glan-dis, which is the continuation of that of the urethra.

Fig. 4. Represents the Female Organs of Generation.

a, That side of the uterus which is next the os sacrum. 1, Its fundus. 2, Its cervix. bb, The Fallopian or uterine tubes, which open into the cavity of the uterus—but the other end is open within the pelvis, and surrounded by cc, The fimbriae. dd, The ovaria. e, The os internum uteri, or mouth of the womb. ff, The ligamenta rotunda, which passes without the belly, and is fixed to the labia pudendi. gg, The cut edges of the ligamenta lata, which connects the uterus to the pelvis. h, The inside of the vagina. i, The orifice of the urethra. k, The clitoris surrounded by (l), The preputium. mm, The labia pudendi. nn, The nymphae.

Fig. 5. Shows the Spermatic ducts of the Testicle filled with Mercury.

A, The vas deferens. B, Its beginning, which forms the posterior part of the epididymis. C, The middle of the epididymis, composed of serpentine ducts. D, The head, or anterior part of the epididymis unravelled. eee, The whole ducts which compose the head of the epididymis unravelled. ff, The vasa deferentia. gg, Rete testis. hh, Some rectilineal ducts which send off the vasa deferentia. ii, The substance of the testicle.

Fig. 6. The Right Testicle entire, and the Epididymis filled with Mercury.

A, The beginning of the vas deferens. B, The vas deferens ascending towards the abdomen. C, The posterior part of the epididymis, named globus minor. D, The spermatic vessels inclosed in cellular substance. E, The body of the epididymis. F, Its head, named globus major. G, Its beginning from the testicle. H, The body of the testicle enclosed in the tunica albuginea. CHAP. IV. OF THE THORAX.

THE thorax, or chest, is that cavity of the trunk which extends from the clavicles, or the lower part of the neck, to the diaphragm; and includes the vital organs, which are the heart and lungs, and likewise the trachea and oesophagus.—This cavity is formed by the ribs and vertebre of the back covered by a great number of muscles, and by the common integuments, and anteriorly by two glandular bodies called the breasts. The spaces between the ribs are filled up by muscular fibres, which from their situation are called intercostal muscles.

SECT. I. Of the Breasts.

The breasts may be defined to be two large conglomerate glands, mixed with a good deal of adipose membrane. The glandular part is composed of an infinite number of minute arteries, veins, and nerves.

The arteries are derived from two different trunks; one of which is called the internal, and the other the external, mammary artery. The first of these arises from the subclavian, and the latter from the axillary.

The veins everywhere accompany the arteries, and are distinguished by the same name. The nerves are chiefly from the vertebral pairs. Like all other conglomerate glands, the breasts are made of a great many small distinct glands, in which the milk is secreted from the ultimate branches of arteries. The excretory ducts of these several glands, gradually uniting as they approach the nipple, form the tubuli lactiferi, which are usually more than a dozen in number, and open at its apex, but have little or no communication, as has been supposed, at the root of the nipple. These ducts, in their course from the glands, are surrounded by a ligamentary elastic substance, which terminates with them in the nipple. Both this substance, and the ducts which it contains, are capable of considerable extension and contraction; but in their natural state are moderately corrugated, so as to prevent an involuntary flow of milk, unless the distending force be very great from the accumulation of too great a quantity.

The whole substance of the nipple is very spongy and elastic; its external surface is uneven, and full of small tubercles. The nipple is surrounded with a disk or circle of a different colour, called the areola; and on the inside of the skin, under the areola, are many sebaceous glands, which pour out a mucous to defend the areola and nipple; for the skin upon these parts is very thin; and the nervous papillae lying very bare, are much exposed to irritation.

The breasts are formed for the secretion of milk, which is destined for the nourishment of the child for some time after its birth. This secretion begins to take place soon after delivery, and continues to flow for many months in very large quantities, if the woman suckles her child.

The operation of suction depends on the principles of the air-pump, and the flow of milk through the lactiferous tubes is facilitated by their being stretched out.

The milk, examined chemically, appears to be composed of oil, mucilage, and water, and of a considerable quantity of sugar. The generality of physiologists have supposed that, like the chyle, it frequently retains the properties of the aliment and medicines taken into the stomach; but it has been proved by experiment that this supposition is ill founded.

SECT. II. Of the Pleura.

The cavity of the thorax is everywhere lined by a membrane of a firm texture called pleura. It is composed of two distinct portions or bags, which, by being applied to each other laterally, form a septum called mediastinum; which divides the cavity into two parts, and is attached posteriorly to the vertebre of the back, and anteriorly to the sternum. But the two laminae of which this septum is formed, do not everywhere adhere to each other; for at the lower part of the thorax they are separated to afford a lodgment to the heart; and at the upper part of the cavity, they receive between them the thymus.

The pleura is plentifully supplied with arteries and veins from the internal mammary and the intercostals. Its nerves, which are very inconsiderable, are derived chiefly from the dorsal and intercostal nerves.

The surface of the pleura, like that of the peritoneum and other membranes lining cavities, is constantly bedewed with a serous moisture (wv), which prevents adhesions of the viscera.

The mediastinum, by dividing the breast into two cavities, obviates many inconveniences, to which we should otherwise be liable. It prevents the two lobes of the lungs from compressing each other when we lie on one side; and consequently contributes to the freedom of respiration, which is disturbed by the least pressure on the lungs. If the point of a sword penetrates between the ribs into the cavity of the thorax, the lungs on that side cease to perform their office; because the air being admitted through the wound, prevents the dilatation of that lobe; while the other lobe, which is separated from it by the mediastinum, remains unhurt, and continues to perform its function as usual.

SECT. III. Of the Thymus.

The thymus is a glandular substance, the use of which is not perfectly ascertained, its excretory duct not

(w) When this fluid is exhaled in too great a quantity, or is not properly carried off, it accumulates and constitutes the hydrops pectoris. not having yet been discovered. It is of an oblong figure, and is larger in the fetus and in young children than in adults, being sometimes nearly effaced in very old subjects. It is placed in the upper part of the thorax, between the two laminae of the mediastinum; but at first is not altogether contained within the cavity of the chest, being found to border upon the upper extremity of the sternum.

Sect. IV. Of the Diaphragm.

The cavity of the thorax is separated from that of the abdomen by a fleshy and membranous septum called the diaphragm or midriff. The greatest part of it is composed of muscular fibres; and on this account systematic writers usually place it very properly among the muscles. Its middle part is tendinous, and it is covered by the pleura above, and by the peritoneum below. It seems to have been improperly named septum transversum, as it does not make a plane transverse division of the two cavities, but forms a kind of vault, the fore part of which is attached to the sternum. Laterally it is fixed to the last of the true ribs, and to all the false ribs; and its lower and posterior part is attached to the vertebrae lumborum, where it may be said to be divided into two portions or crura (x).

The principal arteries of the diaphragm are derived from the aorta, and its veins pass into the vena cava. Its nerves are chiefly derived from the cervical pairs. It affords a passage to the vena cava through its tendinous part, and to the oesophagus through its fleshy portion. The aorta passes down behind it between its crura.

The diaphragm not only serves to divide the thorax from the abdomen, but by its muscular structure is rendered one of the chief agents in respiration. When its fibres contract, its convex side, which is turned towards the thorax, becomes gradually flat, and by increasing the cavity of the breast, affords room for a complete dilatation of the lungs, by means of the air which is then drawn into them by the act of inspiration. The fibres of the diaphragm then relax; and as it resumes its former state, the cavity of the thorax becomes gradually diminished, and the air is driven out again from the lungs by a motion contrary to the former one, called expiration.

It is, in some measure, by means of the diaphragm, that we void the faeces at the anus, and empty the urinary bladder. Besides these offices, the acts of coughing, sneezing, speaking, laughing, gaping, and sighing, could not take place without its assistance; and the gentle pressure which all the abdominal viscera receive from its constant and regular motion, cannot fail to assist in the performance of the several functions which were ascribed to those viscera.

Sect. V. Of the Trachea.

The trachea, or wind-pipe, is a cartilaginous and membranous canal, through which the air passes into the lungs. Its upper part, which is called the larynx, is composed of five cartilages. The uppermost of these cartilages is placed over the glottis or mouth of the larynx, and is called epiglottis, which has been before spoken of, as closing the passage to the lungs in the act of swallowing. At the side of the glottis are placed the two arytenoid cartilages, which are of a very complex figure, not easily to be described. The anterior and larger part of the larynx is made up of two cartilages; one of which is called thyroides or scutiformis, from its being shaped like a buckler; and the other cricoides or annularis, from its resembling a ring. Both these cartilages may be felt immediately under the skin; at the fore part of the throat, and the thyroides, by its convexity, forms an eminence called pomum adami, which is usually more considerable in the male than in the female subject.

All these cartilages are united to each other by means of very elastic ligamentous fibres; and are enabled, by the assistance of their several muscles, to dilate or contract the passage of the larynx, and to perform that variety of motion which seems to point out the larynx as the principal organ of the voice; for when the air passes out through a wound in the trachea, it produces no sound.

These cartilages are moistened by a mucus, which seems to be separated by minute glands situated near them. The upper part of the trachea is covered anteriorly and laterally by a considerable body, which is supposed to be of a glandular structure, and from its situation near the thyroid cartilage is called the thyroid gland; though its excretory duct has not yet been discovered, or its real use ascertained.

The glottis is interiorly covered by a very fine membrane, which is moistened by a constant supply of a watery fluid. From the larynx, the canal begins to take the name of trachea or asperia arteria, and extends from thence as far down as the third or fourth vertebra of the back, where it divides into two branches, which are the right and left bronchial tube. Each of these bronchi (y) ramifies through the substance of that lobe of the lungs, to which it is distributed by an infinite number of branches, which are formed of cartilages, separated from each other like those of the trachea, by an intervening membranous and ligamentary substance. Each of these cartilages is of an angular figure; and as they become gradually less and less

(x) Anatomical writers have usually described the diaphragm as being made up of two muscles united by a middle tendon; and these two portions or crura form what they speak of as the inferior muscle, arising from the sides and fore part of the vertebrae.

(y) The right bronchial tube is usually found to be somewhat shorter and thicker than the left; and M. Portal, who has published a memoir on the action of the lungs on the aorta in respiration, observes, that the left bronchial tube is closely contracted by the aorta; and from some experiments he is induced to conclude, that in the first respirations, the air only enters into the right lobe of the lungs. Memoires de l'Academie Royale des Sciences, 1769. in their diameter, the lower ones are in some measure received into those above them, when the lungs, after being inflated, gradually collapse by the air being pushed out from them in expiration. As the branches of the bronchi become more minute, their cartilages become more and more angular and membranous, till at length they are found to be perfectly membranous, and at last become invisible.

The trachea is furnished with fleshy or muscular fibres; some of which pass through its whole extent longitudinally, while the others are carried round it in a circular direction; so that by the contraction or relaxation of these fibres, it is enabled to shorten or lengthen itself, and likewise to dilate or contract the diameter of its passage.

The trachea and its branches, in all their ramifications, are furnished with a great number of small glands which are lodged in their cellular substance, and discharge a mucous fluid on the inner surface of these tubes.

The cartilages of the trachea, by keeping it constantly open, afford a free passage to the air, which we are obliged to be incessantly respiring; and its membranous part, by being capable of contraction and dilatation, enables us to receive and expel the air in a greater or less quantity, and with more or less velocity, as may be required in singing or in declamation. This membranous structure of the trachea posteriorly seems likewise to assist in the descent of the food, by preventing that impediment to its passage down the oesophagus, which might be expected if the cartilages were complete rings.

The trachea receives its arteries from the carotid and subclavian arteries, and its veins pass into the jugulars. Its nerves arise from the recurrent branch of the eighth pair, and from the cervical plexus.

Sect. VI. Of the Lungs.

The lungs fill the greater part of the cavity of the breast. They are of a soft and spongy texture, and are divided into two lobes, which are separated from each other by the mediastinum, and are externally covered by a production of the pleura. Each of these is divided into two or three lesser lobes; and we commonly find three in the right side of the cavity, and two in the left.

To discover the structure of the lungs, it is required to follow the ramifications of the bronchi, which were described in the last section. These becoming gradually more and more minute, at length terminate in the cellular spaces or vesicles, which make up the greatest part of the substance of the lungs, and readily communicate with each other.

The lungs seem to possess but little sensibility. Their nerves, which are small, and few in number, are derived from the intercostal and eighth pair. This last pair having reached the thorax, sends off a branch on each side of the trachea, called the recurrent, which reascends at the back of the trachea, to which it furnishes branches in its ascent, as well as to the oesophagus, but it is chiefly distributed to the larynx and its muscles. By dividing the recurrent and superior laryngeal nerves at their origin, an animal is deprived of its voice.

There are two series of arteries which carry blood to the lungs: these are the arteriae bronchiales, and the pulmonary artery.

The arteriae bronchiales begin usually by two branches; one of which commonly arises from the right intercostal, and the other from the trunk of the aorta; but sometimes there are three of these arteries, and in some subjects only one. The use of these arteries is to serve for the nourishment of the lungs; and their ramifications are seen creeping everywhere on the branches of the bronchi. The blood is brought back from them by the bronchial veins into the vena azygos.

The pulmonary artery and vein are not intended for the nourishment of the lungs; but the blood in its passage through them is destined to undergo some changes, or to acquire certain essential properties (from the action of the air), which it has lost in its circulation through the other parts of the body. The pulmonary artery receives the blood from the right ventricle of the heart; and dividing into two branches, accompanies the bronchi everywhere, by its ramifications through the lungs; and the blood is afterwards conveyed back by the pulmonary vein, which gradually forming a considerable trunk, goes to empty itself into the left ventricle of the heart; so that the quantity of blood which enters into the lungs, is perhaps greater than that which is sent in the same proportion of time through all the other parts of the body.

Sect. VII. Of Respiration.

Respiration constitutes one of those functions which are properly termed vital, as being essential to life; for to live and to breathe are in fact synonymous terms. It consists in an alternate contraction and dilatation of the thorax, by first inspiring air into the lungs, and then expelling it from them in expiration.

It will perhaps be easy to distinguish and point out the several phenomena of respiration; but to explain their physical cause will be attended with difficulty: for it will naturally be inquired, how the lungs, when emptied of the air, and contracted by expiration, become again inflated, they themselves being perfectly passive? How the ribs are elevated in opposition to their own natural situation? and why the diaphragm is contracted downwards towards the abdomen? Were we to assert that the air, by forcing its way into the cavity of the lungs, dilated them, and consequently elevated the ribs and pressed down the diaphragm, we should speak erroneously. What induces the first inspiration, it is not easy to ascertain; but after an animal has once respired, it would seem likely that the blood, after expiration, finding its passage through the lungs obstructed, becomes a stimulus, which induces the intercostal muscles and the diaphragm to contract, and enlarge the cavity of the thorax, in consequence perhaps of a certain nervous influence, which we will not here attempt to explain. The air then rushes into the lungs; every branch of the bronchial tubes, and all the cellular spaces into which they open, become fully dilated; and the pulmonary vessels being equally distended, the blood flows through them with ease. But as the stimulus which first occasioned this dilatation ceases to operate, the muscles gradually contract; the diaphragm rises upwards again, and diminishes the cavity of the chest; the ribs return to their former state; and as the air passes out in expiration, the lungs gradually collapse, and a resistance of the passage to the blood again takes place. But the heart continuing to receive and expel the blood, the pulmonary artery begins again to be distended, the stimulus is renewed, and the same process is repeated, and continues to be repeated, in a regular succession, during life: for though the muscles of respiration, having a mixed motion, are (unlike the heart) in some measure dependent on the will, yet no human being, after having once respired, can live many moments without it. In an attempt to hold one's breath, the blood soon begins to distend the veins, which are unable to empty their contents into the heart; and we are able only, during a very little time, to resist the stimulus to inspiration. In drowning, the circulation seems to be stopped upon this principle; and in hanging, the pressure made on the jugular veins, may cooperate with the stoppage of respiration in bringing on death.

Till within these few years physiologists were entirely ignorant of the use of respiration. It was at length discovered in part by the illustrious Dr Priestley. He found that the air expired by animals was phlogisticated; and that the air was fitter for respiration, or for supporting animal life, in proportion as it was freer from the phlogistic principle. It had long been observed that the blood in passing through the lungs acquired a more florid colour. He therefore suspected, that it was owing to its having imparted phlogiston to the air; and he satisfied himself of the truth of this idea by experiments, which showed, that the crassamentum of extravasated blood phlogisticated air in proportion as it lost its dark colour. He farther found, that blood thus reddened had a strong attraction for phlogiston; insomuch that it was capable of taking it from phlogisticated air, thereby becoming of a darker colour. From hence it appeared that the blood, in its circulation through the arterial system, imbibes a considerable quantity of phlogiston, which is discharged from it to the air in the lungs.

This discovery has since been prosecuted by two very ingenious physiologists, Dr Crawford and Mr Elliot. It has been shown by Professors Black and Irvine, that different bodies have different capacities for containing fire. For example, that oil and water, when equally hot to the sense and the thermometer, contain different proportions of that principle; and that unequal quantities of it are required, in order to raise those substances to like temperatures. The inquiries of Dr Crawford and Mr Elliot tend to prove, that the capacities of bodies for containing fire are diminished by the addition of phlogiston, and increased by its separation: the capacity of calx of antimony, for example, being greater than that of the antimony itself. Common air contains a great quantity of fire; combustible bodies very little. In combustion, a double elective attraction takes place; the phlogiston of the body being transferred to the air, the fire contained in the air to the combustible body. But as the capacity of the latter is not increased so much as that of the former is diminished, only part of the extricated fire will be absorbed by the body. The remainder therefore will raise the temperature of the compound; and hence we may account for the heat attending combustion. As the use of respiration is to deplogisticate the blood, it seems probable, that a like double elective attraction takes place in this process: the phlogiston of the blood being transferred to the air, and the fire contained in the air to the blood; but with this difference, that the capacities being equal, the whole of the extricated fire is absorbed by the latter. The blood in this state circulating through the body, imbibes phlogiston, and of course gives out its fire; part only of which is absorbed by the parts furnishing the phlogiston, the remainder, as in combustion, becoming sensible; and is therefore the cause of the heat of the body, or what is called animal heat.

In confirmation of this doctrine it may be observed, that the venous blood contains less fire than the arterial; combustible bodies less than incombustible ones; and that air contains less of this principle, according as it is rendered, by combination with phlogiston, less fit for respiration.

In ascending very high mountains, respiration is found to become short and frequent, and sometimes to be attended with a spitting of blood. These symptoms seem to be occasioned by the air being too rare and thin to dilate the lungs sufficiently; and the blood gradually accumulating in the pulmonary vessels, sometimes bursts through their coats and is brought up by coughing. This has likewise been accounted for in a different way, by supposing that the air contained in the blood, not receiving an equal pressure from that of the atmosphere, expands, and at length ruptures the very minute branches of the pulmonary vessels; upon the same principle that fruits and animals put under the receiver of an air-pump, are seen to swell as the outer air becomes exhausted. But the late Dr Darwin published some experiments, in which he attempted to prove, that no air or elastic vapour does exist in the blood-vessels, as has been generally supposed; and he is induced to impute the spitting of blood which has sometimes taken place in ascending high mountains, to accident, or to violent exertions; as it never happens to animals that are put into the exhausted receiver of an air-pump, where the diminution of pressure is many times greater than on the summit of the highest mountains.

Sect. VIII. Of the Voice.

Respiration has already been described as affording us many advantages; and next to that of life, its most important use seems to be that of forming the voice and speech. The ancients, and almost all the moderns, have considered the organ of speech as a kind of musical instrument, which may be compared to a flute, to an hautboy, to an organ, &c. and they argue after the following manner:

The trachea, which begins at the root of the tongue, and goes to terminate in the lungs, may be compared to

(z) See Crawford's Experiments and Observations on Animal Heat, and Elliot's Philosophical Observations. Vol. II, Part I. to the pipe of an organ; the lungs dilating like bellows during the time of inspiration; and as the air is driven out from them in inspiration, it finds its passage strengthened by the cartilages of the larynx, against which it strikes. As these cartilages are more or less elastic, they occasion in their turn more or less vibration in the air, and thus produce the sound of the voice; the variation in the sound and tone of which depends on the state of the glottis, which, when strained, produces an acute tone, and a grave one when dilated.

M. Fercin communicated to the French Academy of Sciences a very ingenious theory on the formation of the voice. He considered the organ of the voice as a string as well as a wind instrument; so that what art has hitherto been unable to construct, and what both the fathers Mersenne and Kircher so much wished to see, M. Fercin imagined he had at length discovered in the human body. He observes, that there are at the edges of the glottis certain tendinous chords, placed horizontally across it, which are capable of considerable vibration, so as to produce sound, in the same manner as it is produced by the strings of a violin or a harpsichord; and he supposes that the air, as it passes out from the lungs, acts as a bow on these strings, while the efforts of the breast and lungs regulate its motion, and produce the variety of tones. So that, according to this system, the variation in the voice is not occasioned by the dilatation or contraction of the glottis, but by the distension or relaxation of these strings, the sound being more or less acute in proportion as they are more or less stretched out. Another writer on this subject supposes, that the organ of voice is a double instrument, which produces in unison two sounds of a different nature; one by means of the air, and the other by means of the chords of the glottis. Neither of these systems, however, is universally adopted. They are both liable to insuperable difficulties; so that the manner in which the voice is formed has never yet been satisfactorily ascertained: we may observe, however, that the sound produced by the glottis is not articulated. To effect this, it is required to pass through the mouth, where it is differently modified by the action of the tongue, which is either pushed against the teeth, or upwards towards the palate; detaining it in its passage, or permitting it to flow freely, by contracting or dilating the mouth.

**Sect. IX. Of Dejection.**

By dejection we mean the act of voiding the faeces at the anus; and an account of the manner in which this is conducted was reserved for this part of the work, because it seemed to require a knowledge of respiration to be perfectly understood.

The intestines were described as having a peristaltic motion, by which the faeces were gradually advancing towards the anus. Now, whenever the faeces are accumulated in the intestine rectum in a sufficient quantity to become troublesome, either by their weight or acrimony, they excite a certain uneasiness which induces us to go to stool.—To effect this, we begin by making a considerable inspiration; in consequence of which the diaphragm is carried downwards towards the lower belly; the abdominal muscles are at the same time contracted in obedience to the will: and the intestines being compressed on all sides, the resistance of the sphincter is overcome, and the faeces pass out at the anus; which is afterwards drawn up by its longitudinal fibres, which are called levatores ani; and then by means of its sphincter is again contracted: but it sometimes happens, as in dysenteries for instance, that the faeces are very liquid, and have considerable acrimony; and then the irritation they occasion is more frequent, so as to promote their discharge without any pressure from the diaphragm or abdominal muscles; and sometimes involuntarily, as is the case when the sphincter becomes paralytic.

**Sect. X. Of the Pericardium, and of the Heart and its Auricles.**

The two membranous bags of the pleura, which were described as forming the mediastinum, recede one from the other, so as to afford a lodgment to a firm membranous sac, in which the heart is securely lodged; this sac, which is the pericardium, appears to be composed of two tunics, united to each other by cellular membrane.—The outer coat, which is thick, and in some places of a tendinous complexion, is a production of the mediastinum; the inner coat, which is extremely thin, is reflected over the auricles and ventricles of the heart, in the same manner as the tunica conjunctiva, after lining the eyelids, is reflected over the eye.

This bag adheres to the tendinous part of the diaphragm, and contains a coagulable lymph, the liquor pericardii, which serves to lubricate the heart and facilitate its motion; and seems to be secreted and absorbed in the same manner as it is in the other cavities of the body.

The arteries of the pericardium are derived from the phrenic, and its veins pass into veins of the same name; its nerves are likewise branches of the phrenic.

The size of the pericardium is adapted to that of the heart, being usually large enough to contain it loosely. As its cavity does not extend to the sternum, the lungs cover it in inspiration; and as it everywhere invests the heart, it effectually secures it from being injured by lymph, pus, or any other fluid, extravasated into the cavities of the thorax.

The heart is a hollow muscle of a conical shape, situated transversely between the two laminae of the mediastinum, at the lower part of the thorax; having its basis turned towards the right side, and its point or apex towards the left.—Its lower surface is somewhat flattened towards the diaphragm. Its basis, from which the great vessels originate, is covered with fat; and it has two hollow and fleshy appendages, called auricles.—Round these several openings, the heart seems to be of a firm ligamentous texture, from which all its fibres seem to originate; and as they advance from thence towards the apex, the substance of the heart seems to become thinner.

The heart includes two cavities or ventricles, which are separated from each other by a fleshy septum; one of these is called the right, and the other the left, ventricle; though perhaps, with respect to their situation, it would be more proper to distinguish them into the anterior and posterior ventricles. The heart is exteriorly covered by a very fine membrane; and its structure is perfectly muscular or fleshy, being composed of fibres which are described as passing in different directions; some as being extended longitudinally from the basis to the apex; others, as taking an oblique or spiral course; and a third sort as being placed in a transverse direction (A).—Within the two ventricles we observe several furrows; and there are likewise tendinous strings, which arise from fleaky columns in the two cavities, and are attached to the valves of the auricles: That the use of these and the other valves of the heart may be understood, it must be observed, that four large vessels pass out from the basis of the heart, viz. two arteries and two veins; and that each of these vessels is furnished with a thin membranous production, which is attached all round to the borders of their several orifices, from whence hanging loosely down they appear to be divided into two or three distinct portions. But as their uses in the arteries and veins are different, so are they differently disposed. Those of the arteries are intended to give way to the passage of the blood into them from the ventricles, but to oppose its return: and, on the contrary, the valves of the veins are constructed so as to allow the blood only to pass into the heart. In consequence of these different uses, we find the valves of the pulmonary artery and of the aorta attached to the orifices of those vessels, so as to have their concave surfaces turned towards the artery; and their convex surfaces, which mutually meet together, being placed towards the ventricle, only permit the blood to pass one way, which is into the arteries. There are usually three of these valves belonging to the pulmonary artery, and as many to the aorta; and from their figure they are called valvulae semilunares. The communication between the two great veins and the ventricles is by means of the two appendages or auricles into which the blood is discharged; so that the other valves which may be said to belong to the veins, are placed in each ventricle, where the auricle opens into it. The valves in the right ventricle are usually three in number, and are named valvulae tricuspidales; but in the left ventricle we commonly observe only two, and these are the valvulae mitrales. The membranes which form these valves in each cavity are attached so as to project somewhat forward; and both the tricuspidales and the mitrales are connected with the tendinous strings, which were described as arising from the fleaky columns. By the contraction of either ventricle the blood is driven into the artery which communicates with that ventricle; and these tendinous strings being gradually relaxed as the sides of the cavity are brought nearer to each other, the valves naturally close the opening into the auricle, and the blood necessarily directs its course into the then only open passage, which is into the artery; but after this contraction the heart becomes relaxed, the tendinous strings are again stretched out, and, drawing the valves of the auricle downwards, the blood is poured by the veins into the ventricle, from whence, by another contraction, it is again thrown into the artery, as will be described hereafter. The right ventricle is not quite so long, though somewhat larger than the left; but the latter has more substance than the other; and this seems to be, because it is intended to transmit the blood to the most distant parts of the body, whereas the right ventricle distributes it only to the lungs.

The heart receives its nerves from the par vagum and the intercostals. The arteries which serve for its nourishment are two in number, and arise from the aorta. They surround in some measure the basis of the heart, and from this course are called the coronary arteries. From these arteries the blood is returned by veins of the same name into the auricles, and even into the ventricles.

The muscular bags called the auricles are situated at the basis of the heart, at the sides of each other; and, corresponding with the two ventricles, are like those two cavities distinguished into right and left. These sacs, which are anteriorly unequal, have externally a jagged appendix; which, from its having been compared to the extremity of an ear, has given them their name of auricles.

Sect. XI. Angiology, or a Description of the Blood Vessels.

The heart has been described as contracting itself, and throwing the blood from its two ventricles into the pulmonary artery and the aorta, and then as relaxing itself and receiving a fresh supply from two large veins, which are the pulmonary vein and the vena cava. We will now point out the principal distributions of these vessels.

The pulmonary artery arises from the right ventricle by a large trunk, which soon divides into two considerable branches, which pass to the right and left lobes of the lungs: each of these branches is afterwards divided and subdivided into an infinite number of branches and ramifications, which extend through the whole substance of the lungs; and from these branches the blood is returned by the veins, which, contrary to the course of the arteries, begin by very minute canals, and gradually become larger, forming at length four large trunks called pulmonary veins, which terminate in the left auricle by one common opening, from whence the blood passes into the left ventricle. From this same ventricle arises the aorta or great artery, which at its beginning is nearly an inch in diameter: it soon sends off two branches, the coronaries, which go to be distributed to the heart and its auricles. After this, at or about the third or fourth vertebra of the back, it makes a considerable curvature; from this curvature (B) arise three arteries; one

(A) Authors differ about the course and distinctions of these fibres; and it seems right to observe, that the structure of the heart being more compact than that of other muscles, its fibres are not easily separated.

(B) Anatomists usually call the upper part of this curvature aorta ascendens; and the other part of the artery to its division at the iliacs, aorta descendens; but they differ about the place where this distinction is to be introduced; and it seems sufficiently to answer every purpose, to speak only of the aorta and its curvature. of which soon divides into two branches. The first two are the left subclavian and the left carotid, and the third is a common trunk to the right subclavian and right carotid; though sometimes both the carotids arise distinctly from the aorta.

The two carotids ascend with the subclavians, along the sides of the trachea; and when they have reached the larynx, divide into two principal branches, the internal and external carotid. The first of these runs a little way backwards in a bending direction; and having reached the under part of the ear, passes through the canal in the os petrosum, and entering into the cavity of the cranium, is distributed to the brain and the membranes which envelop it, and likewise to the eye. The external carotid divides into several branches, which are distributed to the larynx, pharynx, and other parts of the neck; and to the jaws, lips, tongue, eyes, temples, and all the external parts of the head.

Each subclavian is likewise divided into a great number of branches. It sends off the vertebral artery, which passes through the openings we see at the bottom of the transverse processes of the vertebrae of the neck, and in its course sends off many ramifications to the neighbouring parts. Some of its branches are distributed to the spinal marrow, and after a considerable inflection it enters into the cranium, and is distributed to the brain. The subclavian likewise sends off branches to the muscles of the neck and scapula; and the mediastinum, thymus, pericardium, diaphragm, the breast and the muscles of the thorax, and even of the abdomen, derive branches from the subclavian, which are distinguished by different names, alluding to the parts to which they are distributed; as the mammary, the phrenic, the intercostal, &c. But notwithstanding the great number of branches which have been described as arising from the subclavian, it is still a considerable artery when it reaches the axilla, where it drops its former name, which alludes to its passage under the clavicle, and is called the axillary artery; from which a variety of branches are distributed to the muscles of the breast, scapula, and arm.—But its main trunk taking the name of brachialis, runs along on the inside of the arm near the os humeri, till it reaches the joint of the fore arm, and then it divides into two branches. This division, however, is different in different subjects; for in some it takes place higher up, and in others lower down. When it happens to divide above the joint, it may be considered as a happy disposition in case of an accident by bleeding; for supposing the artery to be unfortunately punctured by the lancet, and that the haemorrhage could only be stopped by making a ligature on the vessel, one branch would remain unhurt, through which the blood would pass uninterrupted to the fore arm and hand. One of the two branches of the brachialis plunges down under the flexor muscles, and runs along the edge of the ulna; while the other is carried along the outer surface of the radius, and is easily felt at the wrist, where it is only covered by the common integuments. Both these branches commonly unite in the palm of the hand, and form an arterial arch, from whence branches are detached to the fingers.

The aorta, after having given off at its curvature the carotids and subclavians which convey blood to all the upper parts of the body, descends upon the bodies of the vertebrae a little to the left, as far as the os sacrum, where it drops the name of aorta, and divides into two considerable branches. In this course, from its curvature to its bifurcation, it sends off several arteries in the following order: 1. One or two little arteries, first demonstrated by Ruysch as going to the bronchi, and called arteriae bronchiales Ruyschii. 2. The arteriae cesophagei. These are commonly three or four in number. They arise from the fore part of the aorta, and are distributed chiefly to the cesophagus. 3. The inferior intercostal arteries, which are distributed between the ribs in the same manner as the arteries of the three or four superior ribs are, which are derived from the subclavian. These arteries send off branches to the medulla spinalis. 4. The diaphragmatic or inferior phrenic arteries, which go to the diaphragm, stomach, omentum, duodenum, pancreas, spleen, liver, and gall-bladder. 5. The celiac, which sends off the coronary stomachic, the splenic, and the hepatic artery. 6. The superior mesenteric artery, which is distributed to the mesentery and small intestines. 7. The emulsives, which go to the kidneys. 8. The arteries which are distributed to the glandulae renales. 9. The spermatic. 10. The inferior mesenteric artery, which ramifies through the lower portion of the mesentery and the large intestines. A branch of this artery which goes to the rectum is called the internal hemorrhoidal. 11. The lumbar arteries, and a very small branch called the sacra, which are distributed to the muscles of the loins and abdomen, and to the os sacrum and medulla spinalis.

The trunk of the aorta, when it has reached the last vertebra lumborum, or the os sacrum, drops the name of aorta, and separates into two forked branches called the iliacs. Each of these soon divides into two branches; one of which is called the internal iliac, or hypogastric artery, and is distributed upon the contents of the pelvis and upon the muscles on its outer side. One branch, called pudenda communis, sends small ramifications to the end of the rectum under the name of hemorrhoidales externae, and is afterwards distributed upon the penis. The other branch, the external iliac, after having given off the circumflex artery of the os ilium and the epigastric, which is distributed to the recti muscles, passes out of the abdomen under Poupart's ligament, and takes the name of crural artery. It descends on the inner part of the thigh close to the os femoris, sending off branches to the muscles, and then sinking deeper in the hind part of the thigh, reaches the ham, where it takes the name of popliteal: after this it separates into two considerable branches; one of which is called the anterior tibial artery; the other divides into two branches, and these arteries all go to be distributed to the leg and foot.

The blood, which is thus distributed by the aorta to all parts of the body, is brought back by the veins, which are supposed to be continued from the ultimate branches of arteries; and uniting together as they approach the heart, at length form the large trunks, the vena cava ascendens, and vena cava descendens.

All the veins which bring back the blood from the upper extremities, and from the head and breast, pass into the vena cava descendens; and those which return it from the lower parts of the body terminate in the of the vena cava ascendens; and these two cavas uniting together, as they approach the heart, open by one common orifice into the left auricle.

It does not here seem to be necessary to follow the different divisions of the veins as we did those of the arteries; and it will be sufficient to remark, that in general every artery is accompanied by its vein, and that both are distinguished by the same name. But, like many other general rules, this too has its exceptions (c). The veins, for instance, which accompany the external and internal carotid, are not called the carotid veins, but the external and internal jugular. In the thorax there is a vein distinguished by a proper name, and this is the azygos, or vena sine pari. This vein, which is a pretty considerable one, runs along by the right side of the vertebrae of the back, and is chiefly destined to receive the blood from the intercostals on that side, and from the lower half of those on the left side, and to convey it into the vena cava descendens. In the abdomen we meet with a vein, which is a still more remarkable one, and this is the vena portae, which performs the office both of an artery and a vein. It is formed by a reunion of all the veins which come from the stomach, intestines, omentum, pancreas, and spleen, so as to compose one great trunk, which goes to ramify through the liver; and after having deposited the bile, its ramifications unite, and bring back into the vena cava, not only the blood which the vena portae had carried into the liver, but likewise the blood from the hepatic artery. Every artery has a vein which corresponds with it; but the trunks and branches of the veins are more numerous than those of the arteries. The reasons for this disposition are perhaps not difficult to be explained; the blood in its course through the veins is much farther removed from the source and cause of its motion, which are in the heart, than it was when in the arteries; so that its course is consequently less rapid, and enough of it could not possibly be brought back to the heart in the moment of its dilatation, to equal the quantity which is driven into the arteries from the two ventricles at the time they contract; and the equilibrium, which is so essential to the continuance of life and health, would consequently be destroyed, if the capacity of the veins did not exceed that of the arteries, in the same proportion that the rapidity of the blood's motion through the arteries exceeds that of its return through the veins.

A large artery ramifying through the body, and continued to the minute branches of veins, which gradually unite together to form a large trunk, may be compared to two trees united to each other at their tops; or rather as having their ramifications so disposed that the two trunks terminate in one common point; and if we farther suppose, that both these trunks and their branches are hollow, and that a fluid is incessantly circulated through them, by entering into one of the trunks and returning through the other, we shall be enabled to conceive how the blood is circulated through the vessels of the human body.

Every trunk of an artery, before it divides, is nearly cylindrical, or of equal diameter through its whole length, and so are all its branches when examined separately. But every trunk seems to contain less blood than the many branches do into which that trunk separates; and each of these branches probably contains less blood than the ramifications do into which it is subdivided; and it is the same with the veins; the volume of their several ramifications, when considered together, being found to exceed that of the great trunk which they form by their union.

The return of the blood through the veins to the heart, is promoted by the action of the muscles, and the pulsation of the arteries. And this return is likewise greatly assisted by the valves which are to be met with in the veins, and which constitute one of the great distinctions between them and the arteries. These valves, which are supposed to be formed by the inner coat of the veins, permit the blood to flow from the extremities towards the heart, but oppose its return. They are most frequent in the smaller veins. As the column of blood increases, they seem to become less necessary; and therefore in the vena cava ascendens, we meet with only one valve, which is near its origin.

The arteries are composed of several tunics. Some writers enumerate five of these tunics; but perhaps we may more properly reckon only three, viz. the nervous, muscular, and cuticular coats. The veins are by some anatomists described as having the same number of coats as the arteries; and as they do not seem to be irritable, we cannot with propriety suppose them to have a muscular tunic. We are aware of Dr Verschuir's experiments to prove that the jugular and some other veins possess a certain degree of irritability; but it is certain, that his experiments, repeated by others, have produced a different result; and even he himself allows, that sometimes he was unable to distinguish any such property in the veins. Both these series of vessels are nourished by still more minute arteries and veins, which are seen creeping over their coats and ramifying through their whole substance, and are called vasa vasorum; they have likewise many minute branches of nerves.

The arteries are much stronger than the veins; and they seem to require this force, to be enabled to resist the impetus with which the blood circulates through them, and to impel it on towards the veins.

When the heart contracts, it impels the blood into the arteries, and sensibly distends them; and these vessels again contract, as the heart becomes relaxed to receive more blood from the auricles; so that the cause of the contraction and dilatation of the arteries seems to be easy to be understood, being owing in part to their own contractile power, and in part to the action of the heart; but in the veins, the effects of this impulse not being so sensibly felt, and the vessels themselves having little or no contractile power, the blood seems to flow in a constant and equal stream; and this, together with its passing gradually from a small channel into a larger one, seems to be the reason why the veins

(c) In the extremities, some of the deep-seated veins, and all the superficial ones, take a course different from that of the arteries. veins have no pulsatory motion, except the large ones near the heart; and in these it seems to be occasioned by the motion of the diaphragm, and by the regurgitation of the blood in the cavas.

Sect. XII. Of the Action of the Heart, Auriclet, and Arteries.

The heart, at the time it contracts, drives the blood from the ventricles into the arteries; and the arteries being thus filled and distended, are naturally inclined to contract the moment the heart begins to dilate, and ceases to supply them with blood. These alternate motions of contraction and dilatation of the heart and arteries, are distinguished by the name of systole and diastole. When the heart is in a state of contraction or systole, the arteries are at that instant distended with blood, and in their diastole; and it is in this state we feel their pulsatory motion, which we call the pulse. When the heart dilates, and the arteries contract, the blood is impelled onwards into the veins, through which it is returned back to the heart. While the heart, however, is in its systole, the blood cannot pass from the veins into the ventricles, but is detained in the auricles, which are two reservoirs formed for this use, till the diastole, or dilatation of the heart, takes place; and then the distended auricles contract, and drive the blood into the ventricles; so that the auricles have an alternate systole and diastole as well as the heart.

Although both the ventricles of the heart contract at the same time, yet the blood passes from one to the other. In the same moment, for instance, that the left ventricle drives the blood into the aorta, the right ventricle impels it into the pulmonary artery, which is distributed through all the substance of the lungs. The blood is afterwards brought back into the left ventricle by the pulmonary vein at the same time that the blood is returned by the cavas, into the right ventricle, from all the other parts of the body.

This seems to be the mode of action of the heart and its vessels: but the cause of this action has, like all other intricate and interesting subjects, been differently explained. It seems to depend on the stimulus made on the different parts of the heart by the blood itself, which, by its quantity and heat, or other properties (D), is perhaps capable of first exciting that motion, which is afterwards continued through life, independent of the will, by a regular return of blood to the auricles, in a quantity proportioned to that which is thrown into the arteries.

The heart possesses the vis insita, or principle of irritability, in a much greater degree than any other muscle of the body. The pulse is quicker in young than in old subjects, because the former are cat. par. more irritable than the latter. Upon the same principle we may explain, why the pulse is constantly quicker in weak than in robust persons.

(D) Dr Harvey long ago suggested, that the blood is possessed of a living principle; and the late Mr J. Hunter has endeavoured to revive this doctrine; in support of which he has adduced many ingenious arguments. The subject is a curious one, and deserves to be prosecuted as an inquiry which cannot but be interesting to physiologists.

(E) The blood, as it flows through the arteries, is observed to be more florid than it is in the veins; and this redness is acquired in its passage through the lungs. Vid. Sect. VII.

Sect. XIII. Of the Circulation.

After what has been observed of the structure and action of the heart and its auricles, and likewise of the arteries and veins, there seem to be but very few arguments required to demonstrate the circulation of the blood, which has long since been established as a medical truth. This circulation may be defined to be a perpetual motion of the blood, in consequence of the action of the heart and arteries, which impel it through all the parts of the body, from whence it is brought back by the veins to the heart.

A very satisfactory proof of this circulation, and a proof easy to be understood, may be deduced from the different effects of pressure on an artery and a vein. If a ligature, for instance, is passed round an artery, the vessel swells considerably between the ligature and the heart; whereas if we tie up a vein, it only becomes filled between the extremity and the ligature, and this is what we every day observe in bleeding. The ligature we pass round the arm on these occasions, compresses the superficial veins; and the return of the blood through them being impeded, they become distended. When the ligature is too loose, the veins are not sufficiently compressed, and the blood continues its progress towards the heart; and, on the contrary, when it is made too tight, the arteries themselves become compressed; and the flow of the blood through them being impeded, the veins cannot be distended.

Another phenomenon, which effectually proves the circulation, is the loss of blood that every living animal sustains by opening only a single artery of a moderate size; for it continues to flow from the wounded vessel till the equilibrium is destroyed which is essential to life. This truth was not unknown to the ancients; and it seems strange that it did not lead them to a knowledge of the circulation, as it sufficiently proves, that all the other vessels must communicate with that which is opened. Galen who lived more than 1500 years ago, drew this conclusion from it; and if we further observe, that he describes (after Erasistratus, who flourished about 450 years before him) the several valves of the heart, and determines their disposition and uses, it will appear wonderful, that a period of near 2000 years should afterwards elapse before the true course of the blood was ascertained. This discovery, for which we are indebted to the immortal Harvey, has thrown new lights on physiology and the doctrine of diseases, and constitutes one of the most important periods of anatomical history.

Sect XIV. Of the Nature of the Blood.

Blood, recently drawn from a vein into a basin, would seem to be an homogeneous fluid of a red colour (E); but when suffered to rest, it soon coagulates, and divides into two parts, which are distinguished by the names of crassamentum and serum. The crassamentum is the red coagulum, and the serum is the water in which it floats. Each of these may be again separated into two others; for the crassamentum, by being repeatedly washed in warm water, gives out all its red globules, and what remains appears to be composed of the coagulable lymph (γ), which is a gelatinous substance, capable of being hardened by fire till it becomes perfectly horny: and if we expose the serum to a certain degree of heat, part of it will be found to coagulate like the white of an egg, and there will remain a clear and limpid water, resembling urine both in its appearance and smell.

The serum and crassamentum differ in their proportion in different constitutions; in a strong person, the crassamentum is in a greater proportion to the serum than in a weak one *; and the same difference is found to take place in diseases (c).

Sect. XV. Of Nutrition.

The variety of functions which we have described as being incessantly performed by the living body, and the continual circulation of the blood through it, must necessarily occasion a constant dissipation of the several parts which enter into its composition. In speaking of the insensible perspiration, we observed how much was incessantly passing off from the lungs and the surface of the skin. The discharge by urine is likewise every day considerable; and great part of the bile, saliva, &c., are excluded by stool. But the solid, as well as the fluid parts of the body, require a constant renewal of nutritious particles. They are exposed to the attrition of the fluids which are circulated through them; and the contraction and relaxation they repeat so many thousand times in every day, would necessarily occasion a dissolution of the machine, if the renewal was not proportioned to the waste.

It is easy to conceive how the chyle formed from the aliment is assimilated into the nature of blood, and repairs the loss of the fluid parts of our body; but how the solids are renewed, has never yet been satisfactorily explained. The nutritious parts of the blood are probably deposited by the arteries by exudation through their pores into the tela cellulosa; and as the solid parts of the body are in the embryo only a kind of jelly, which gradually acquires the degree of consistence they are found to have when the body arrives at a more advanced age; and these same parts which consist of bones, cartilages, ligaments, muscles, &c., are sometimes reduced again by disease to a gelatinous state; we may, with some degree of probability, consider the coagulable lymph as the source of nutrition.

If the supply of nourishment exceeds the degree of waste, the body increases; and this happens in infancy and in youth: for at those periods, but more particularly the former one, the fluids bear a large proportion to the solids; and the fibres being soft and yielding, are proportionably more capable of extension and increase. But when the supply of nutrition only equals the waste, we neither increase nor decrease; and we find this to be the case when the body has attained its full growth or acme: for the solids having then acquired a certain degree of firmness and rigidity, do not permit a farther increase of the body. But as we approach to old age, rigidity begins to be in excess, and the fluids (ii) bear a much less proportion to the solids than before. The dissipation of the body is greater than the supply of nourishment: many of the smaller vessels become gradually impervious (i); and the fibres losing their moisture and their elasticity, appear flaccid and wrinkled. The lilies and the roses disappear, because the fluids by which they were produced can no longer reach the extremities of the capillary vessels of the skin. As these changes take place, the nervous power being proportionably weakened, the irritability and sensibility of the body, which were formerly so remarkable, are greatly diminished; and in advanced life, the hearing, the eye-sight, and all the other senses, become gradually impaired.

Sect. XVI. Of the Glands and Secretions.

The glands are commonly understood to be small, roundish, or oval bodies, formed by the convoluted of a great number of vessels, and destined to separate particular humours from the mass of blood.

They are usually divided into two classes; but it seems more

(f) It may not be improper to observe, that till of late the coagulable lymph has been confounded with the serum of the blood, which contains a substance that is likewise coagulable, though only when exposed to heat, or combined with certain chemical substances; whereas the other coagulates spontaneously when exposed to the air or to rest.

(g) When the blood separates into serum and crassamentum, if the latter be covered with a crust of a whitish or buff colour, it has been usually considered as a certain proof of the blood's being in a state of too great viscosity. This appearance commonly taking place in inflammatory diseases, has long served to confirm the theory which ascribes the cause of inflammation to lentor and obstructions. But from the late Mr Hewson's experiments it appears, that when the action of the arteries is increased, the blood, instead of being more viscoid, is, on the contrary, more fluid than in the ordinary state previous to inflammation; and that in consequence of this, the coagulable lymph suffers the red globules, which are the heaviest part of the blood, to fall down to the bottom before it coagulates: so that the crassamentum is divided into two parts; one of which is found to consist of the coagulable lymph alone (in this case termed the buff); and the other, partly of this and partly of the red globules.

(h) As the fluids become less in proportion to the solids, their acrimony is found to increase; and this may perhaps compensate for the want of fluidity in the blood, by diminishing its cohesion.

(i) In infancy, the arteries are numerous and large in respect to the veins, and the lymphatic glands are larger than at any other time of life; whereas, in old age, the capacity of the venous system exceeds that of the arteries, and the lymphatic system almost disappears. more proper to distinguish three kinds of glands, viz. the mucous, conglomerate, and conglomerate.

The mucous glands, or follicles as they are most commonly called, are small cylindrical tubes continued from the ends of arteries. In some parts of the body, as in the tonsils, for example, several of these follicles may be seen folded together in one common covering, and opening into one common sinus. These follicles are the vessels that secrete and pour out mucus in the mouth, esophagus, stomach, intestines, and other parts of the body.

The conglomerate glands are peculiar to the lymphatic system. Every lymphatic vein passes through a gland of this kind in its way to the thoracic duct. They are met with in different parts of the body, particularly in the axilla, groin, and mesentery, and are either solitary or in distinct clusters.

The conglomerate glands are of much greater bulk than the conglomerate, and seem to be an assemblage of many smaller glands. Of this kind are the liver, kidneys, &c. Some of them, as the pancreas, parotids, &c., have a granulated appearance. All these conglomerate glands are plentifully supplied with blood vessels; but their nerves are in general very minute, and few in number. Each little granulated portion furnishes a small tube, which unites with other similar ducts, to form the common excretory duct of the gland.

The principal glands, and the humours they secrete, have been already described in different parts of this work; and there only remains for us to examine the general structure of the glands, and to explain the mechanism of secretion. On the first of these subjects two different systems have been formed; each of which has had, and still continues to have, its adherents. One of these systems was advanced by Malpighi, who supposed that an artery entering into a gland ramifies very minutely through its whole substance; and that its branches ultimately terminate in a vesicular cavity or follicle, from whence the secreted fluid passes out through the excretory duct. This doctrine at first met with few opponents; but the celebrated Ruysch, who first attempted minute injections with wax, afterwards disputed the existence of these follicles, and asserted, that every gland appears to be a continued series of vessels, which, after being repeatedly convoluted in their course through its substance, at length terminate in the excretory duct. Anatomists are still divided between these two systems: that of Malpighi, however, seems to be the best founded.

The mode of secretion has been explained in a variety of ways, and they are all perfectly hypothetical. In such an inquiry, it is natural to ask, how one gland constantly separates a particular humour, while another gland secretes one of a very different nature from the blood? The bile, for instance, is separated by the liver, and the urine by the kidneys. Are these secretions to be imputed to any particular dispositions in the fluids? or is their cause to be looked for in the solids?

It has been supposed, that every gland contains within itself a fermenting principle, by which it is enabled to change the nature of the blood it receives, and to endue it with a particular property. Thus, according to this system, the blood, as it circulates through the kidneys, becomes mixed with the fermenting principle of those glands, and a part of it is converted into urine; and again in the liver, in the salivary and other glands, the bile, the saliva, and other juices, are generated from a similar cause. But it seems to be impossible for any liquor to be confined in a place exposed to the circulation, without being carried away by the torrent of blood, every part of which would be equally affected; and this system of fermentation has long been rejected as vague and chimerical. But as the cause of secretion continued to be looked for in the fluids, the former system was succeeded by another, in which recourse was had to the analogy of the humours. It was observed, that if paper be moistened with water, and oil and water be afterwards poured upon it, the water only will be permitted to pass through it; but that, on the other hand, if the paper has been previously soaked in oil instead of water, the oil only, and not the water, will be filtered through it. These observations led to a supposition, that every secretory organ is originally furnished with a humour analogous to that which it is afterwards destined to separate from the blood; and that in consequence of this disposition, the secretory vessels of the liver for instance, will only admit the bilious particles of the blood, while all the other humours will be excluded. This system is an ingenious one, but the difficulties with which it abounds are unanswerable: for oil and water are immiscible; whereas the blood, as it is circulated through the body, appears to be a homogeneous fluid. Every oil will pass through a paper moistened only with one kind of oil; and wine, or spirits mixed with water, will easily be filtered through a paper previously soaked in water. Upon the same principle, all our humours, though differing in their other properties, yet agreeing in that of being perfectly miscible with each other, will all easily pass through the same filter.—But these are not all the objections to this system. The humours which are supposed to be placed in the secretory vessels for the determination of similar particles from the blood, must be originally separated without any analogous fluid; and that which happens once, may as easily happen always. Again, it sometimes happens, from a vicious disposition, that humours are filtered through glands which are naturally not intended to afford them a passage; and when this once has happened, it ought, according to this system, to be expected always to do so; whereas this is not the case; and we are, after all, naturally led to seek for the cause of secretion in the solids. It does not seem right to ascribe it to any particular figure of the secretory vessels; because the soft texture of those parts does not permit them to preserve any constant shape, and our fluids seem to be capable of accommodating themselves to every kind of figure. Some have imputed it to the difference of diameter in the oriaces of the different secretory vessels. To this doctrine objections have likewise been raised; and it has been argued, that the vessels of the liver, for instance, would upon this principle, afford a passage not only to the bile, but to all the other humours of less consistence with it. In reply to this objection, it has been supposed, that secondary vessels exist, which originate from the first, and permit all the humours thinner than the bile to pass through them.

Each of these hypotheses is probably very remote from the truth.

EXPLANATION EXPLANATION OF PLATE XXX.

This Plate represents the Heart in situ, all the large Arteries and Veins, with some of the Muscles, &c.

Muscles, &c.—Superior Extremity.—a, Masseter. b, Complexus. c, Digastricus. d, Os hyoides. e, Thyroid gland. f, Levator scapulae. g, Cucullaris. h, The clavicles cut. i, The deltoid muscle. k, Biceps flexor cubiti cut. l, Coracobrachialis. m, Triceps extensor cubiti. n, The heads of the pronator teres, flexor carpi radialis, and flexor digitorum sublimis, cut. o, The flexor carpi ulnaris cut at its extremity. p, Flexor digitorum profundus. q, Supinator radii longus, cut at its extremity. r, Ligamentum carpi transversale. s, Extensors carpi radiales. t, Latissimus dorsi. u, Anterior edge of the serratus anterior major. vv, The inferior part of the diaphragm. ww, Its interior edge cut. xx, The kidneys. y, Transversus abdominis. z, Os ilium.

Inferior Extremity.—a, Psoas magnus. b, Iliacus internus. c, The fleshy origin of the tensor vaginis femoris. dd, The ossa pubis cut from each other. e, Musculus pectineus cut from its origin. f, Short head of the triceps adductor femoris cut. g, The great head of the triceps. h, The long head cut. i, Vastus internus. k, Vastus externus. l, Cruraceus. m, Gemellus. n, Soleus. o, Tibia. p, Peroneus longus. q, Peroneus brevis. r, Fibula.

Heart and Blood Vessels.—A, The heart, with the coronary arteries and veins. B, The right auricle of the heart. C, The aorta ascendens. D, The left subclavian artery. E, The left carotid artery. F, The common trunk which sends off the right subclavian and right carotid arteries. G, The carotis externa. H, Arteria facialis, which sends off the coronary arteries of the lips. I, Arteria temporalis profunda. K, Aorta descendens. LL, The iliac arteries,—which send off MM, The femoral or crural arteries. N.B. The other arteries in this figure have the same distribution as the veins of the same name:—And generally, in the anatomical plates, the description to be found on the one side points out the same parts in the other.

1, The frontal vein. 2, The facial vein. 3, Vena temporalis profunda. 4, Vena occipitalis. 5, Vena jugularis externa. 6, Vena jugularis interna, covering the arteria carotis communis. 7, The vascular arch on the palm of the hand, which is formed by 8, the radial artery and vein, and, 9, the ulnar artery and vein. 10 10, Cephalic vein. 11, Basilic vein, that on the right side, cut. 12, Median vein. 13, The humeral vein, which, with the median, covers the humeral artery. 14 14, The external thoracic or mammary arteries and veins. 15, The axillary vein, covering the artery. 16 16, The subclavian veins, which, with (66) the jugulars, form. 17, The vena cava superior. 18, The cutaneous arch of veins on the fore part of the foot. 19, The vena tibialis antica, covering the artery. 20, The vena profunda femoris, covering the artery. 21, The upper part of the vena saphena major. 22, The femoral vein. 23 23, The iliac veins. 24 24, Vena cava inferior. 25 25, The renal veins covering the arteries. 26 26, The diaphragmatic veins.

CHAP. V. OF THE BRAIN AND NERVES.

Sect. I. Of the Brain and its Integuments.

The bones of the cranium were described in the osteological part of this work, as enclosing the brain and defending it from external injury; but they are not its only protection; for when we make a horizontal section through these bones, we find this mass everywhere surrounded by two membranes (E), the dura and pia mater.—The first of these lines the interior surface of the cranium, to which it everywhere adheres strongly (r.), but more particularly at the sutures, and at the many foramina through which vessels pass between it and the pericranium. The dura mater (M) is perfectly smooth and inelastic, and its inner surface is constantly bedewed with a fine pellucid fluid, which everywhere separates it from the pia mater. The dura mater sends off

(k) The Greeks called these membranes meninges; but the Arabians, supposing them to be the source of all the other membranes of the body, afterwards gave them the name of dura and pia mater; by which they are now usually distinguished.

(l) In young subjects this adhesion is greater than in adults; but even then, in the healthy subject, it is nowhere easily separable, without breaking through some of the minute vessels by means of which it is attached to the bone.

(m) This membrane is commonly described as consisting of two laminae; of which the external one is supposed to perform the office of periosteum internum to the cranium, while the internal one forms the folds and processes of the dura mater. In the natural state, however, no such separation is apparent; like other membranes, we may indeed divide it, not into two only, but many laminae; but this division is artificial, and depends on the dexterity of the anatomist. off several considerable processes, which divide the brain into several portions, and prevent them from compressing each other. Of these processes there is one superior and longitudinal, called the falx or falceform process, from its resemblance to a scythe. It arises from the spine of the os frontis, near the crista galli, and extending along in the direction of the sagittal suture, to beyond the lambdoidal suture, divides the brain into two hemispheres. A little below the lambdoidal suture, it divides into two broad wings or expansions called the transverse or lateral processes, which prevent the lobes of the cerebrum from pressing on the cerebellum. Besides these there is a fourth, which is situated under the transverse processes, and being continued to the spine of the occiput, divides the cerebellum into two lobes.

The blood, after being distributed through the cavity of the cranium by means of the arteries, is returned, as in the other parts of the body, by veins which all pass on to certain channels situated between these several processes.

These canals or sinuses communicate with each other, and empty themselves into the internal jugular veins, which convey the blood into the vena cava. They are in fact triangular veins, running through the substance of the dura mater, and, like all the processes, are distinguished into longitudinal and lateral; and where these three meet, and where the fourth process passes off, we observe a fourth sinus, which is called torcular; Herophilus, who first described it, having supposed that the blood, at the union of these two veins, is, as it were, in a press.

Besides these four canals, which were known to the ancients, modern anatomists enumerate many others, by giving the appellation of sinuses to other veins of the dura mater, which for the most part empty themselves into some of those we have just now described. There are the inferior longitudinal sinus, the superior and inferior petrous sinuses, the cavernous sinuses, the circular sinus, and the anterior and posterior occipital sinuses.

These sinuses or veins, by being conveyed through a thick dense membrane, firmly suspended, as the dura mater is, within the cranium, are less liable to rupture; at the same time they are well supported, and by running everywhere along the inner surface of the bones, they are prevented from pressing on the substance of the brain. To prevent too great a dilatation of them, we find filaments (called chordee Willisii, from their having been first noticed by Willis) stretched across their cavities; and the oblique manner in which the veins from the brain run through the substance of the brain into these channels, serves the purpose of a valve, which prevents the blood from turning back into the smaller and weaker vessels of the brain.

The pia mater is a much softer and finer membrane than the dura mater: being exceedingly delicate, transparent, and vascular. It invests every part of the brain, and sends off an infinite number of elongations, which insinuate themselves between the convolutions, and even into the substance of the brain. This membrane is composed of two laminae; of which the exterior one is named tunica arachnoidea, from its thinness, which is equal to that of a spider's web. These two laminae are intimately adherent to each other, at the upper part of the brain, but are easily separable at the basis of the brain, and through the whole length of the medulla spinalis. The external layer, or tunica arachnoidea, appears to be spread uniformly over the surface of the brain, but without entering into the furrows as the inner layer does; the latter being found to insinuate itself between the convolutions, and even into the interior cavities of the brain. The blood-vessels of the brain are distributed through it in their way to that organ, and are therefore divided into very minute ramifications, before they penetrate the substance of the brain.

There are several parts included under the general denomination of brain. One of these, which is of the softest consistence, and fills the greatest part of the cavity of the cranium, is the cerebrum or brain properly so called. Another portion, which is seated in the inferior and posterior part of the head, is the cerebellum; and a third, which derives its origin from both these, is the medulla oblongata.

The cerebrum is a medullary mass of a moderate consistence, filling up exactly all the upper part of the cavity of the cranium, and divided into two hemispheres by the falx of the dura mater. Each of these hemispheres is usually distinguished into an anterior, a middle, and a posterior lobe. The first of these is lodged on the orbital processes of the os frontis; the middle lobes lie in the middle fossae of the basis of the cranium, and the posterior lobes are placed on the transverse septum of the os occipitis, immediately over the cerebellum, from which they are separated by the lateral processes of the dura mater. These two portions afford no distinguishing mark of separation; and on this account Haller, and many other modern anatomists, omit the distinction of the middle lobe, and speak only of the anterior and posterior lobes of the brain.

The cerebrum appears to be composed of two distinct substances. Of these the exterior one, which is of a grayish or ash colour, is called the cortex, and is somewhat softer than the other, which is very white, and is called medulla, or substantia alba.

After having removed the falx, and separated the two hemispheres from each other, we perceive a white convex body, the corpus callosum, which is a portion of the medullary substance, uniting the two hemispheres to each other, and not invested by the cortex. By making a horizontal incision into the brain, on a level with this corpus callosum, we discover two oblong cavities, named the anterior or lateral ventricles, one in each hemisphere. These two ventricles, which, communicate with each other by a hole immediately under the plexus choroides, are separated laterally by a very fine medullary partition, called septum lucidum, from its thinness and transparency. The lower edge of this septum is fixed to the fornix, which is a kind of medullary arch (as its name implies) situated under the corpus callosum, and nearly of a triangular shape. Anteriorly the fornix sends off two medullary chords, called its anterior crura; which seem to be united to each other by a portion of medullary substance, named commissura anterior cerebri. These crura diverging from one another, are lost at the outer side of the lower and fore part of the third ventricle. Posteriorly the fornix is formed into two other crura, which unite with two medullary protuberances, called pedes hippocampi, and sometimes cornua ammonis, that extend along the back part of the lateral ventricles. The concave edge of the pedes hippocampi is covered by a medullary lamina, called corpus fimbriatum.

Neither the edges of the fornix, nor its posterior crura, can be well distinguished, till we have removed the plexus choroides. This is a production of the pia mater, which is spread over the lateral ventricles. Its loose edges are collected, so as to appear like a vascular band on each side.

When we have removed this plexus, we discover several other protuberances included in the lateral ventricles. These are the corpora striata, the thalami nervorum opticorum, the tubercula quadrigemina, and the pineal gland.

The corpora striata are two curved oblong eminences, that extend along the anterior part of the lateral ventricles. They derive their name from their striated appearance, which is owing to an intermixture of the cortical and medullary substances of the brain. The thalami nervorum opticorum are so called, because the optic nerves arise chiefly from them, and they are likewise composed both of the cortex and medulla. They are separated from the corpora striata only by a kind of medullary chord, the geminum centrum semicircularis. The thalami are nearly of an oval shape, and are situated at the bottom of the upper cavity of the lateral ventricles. They are closely united, and at their convex part seem to become one body.

Anteriorly, in the space between the thalami, we observe an orifice by which the lateral ventricles communicate, and another leads down from this, under the different appellations of foramen commune anterius, vulva iter ad infundibulum, but more properly inter ad tertium ventriculum; and the separation of the thalami from each other posteriorly, forms another opening or interstice called anus. This has been supposed to communicate with the third ventricle; but it does not, the bottom of it being shut up by the pia mater. The back part of the anus is formed by a kind of medullary band, which connects the thalami to each other, and is called commissura posterior cerebri.

Behind the thalami and commissura posterior, we observe a small, soft, grayish, and oval body, about the size of a pea. This is the glandula pinealis; it is described by Galen under the name of conarium, and has been rendered famous by Descartes, who supposed it to be the seat of the soul. Galen seems formerly to have entertained the same opinion. Some modern writers have, with as little reason, imagined that the soul is placed in the corpus callosum.

The pineal gland rests upon four remarkable eminences, disposed in pairs, and seated immediately below it. These tubercles, which by the ancients were called testes and nates, have, since the time of Winslow, been more commonly named tubercula quadrigemina.

Under the thalami we observe another cavity, the third ventricle, which terminates anteriorly in a small medullary canal, the infundibulum, that leads to the glandula pituitaria. It has been doubted, whether the infundibulum is really hollow; but some late experiments on this part of the brain by Professor Murray of Upsal, clearly prove it to be a medullary canal, surrounded by both laminae of the pia mater. After freezing the brain, this channel was found filled with ice; Cerebri, and De Haen tells us, he found it dilated, and filled with a calcareous matter (N).

The soft spongy body in which the infundibulum terminates, was by the ancients supposed to be of a glandular structure, and destined to filter the serosity of the brain. Spigelius pretended to have discovered its excretory duct, but it seems certain that no such duct exists. It is of an oblong shape, composed, as it were, of two lobes. In ruminant animals it is much larger than in man.

From the posterior part of the third ventricle, we see a small groove or channel, descending obliquely backwards. This channel, which is called the aqueduct of Sylvius, though it was known to the ancients, opens into another cavity of the brain, placed between the cerebellum and medulla oblongata, and called the fourth ventricle.

The cerebellum, which is divided into two lobes, is commonly supposed to be of a firmer texture than the cerebrum; but the truth is, that in the greater number of subjects, there appears to be no sensible difference in the consistence of these two parts. It has more of the cortical than of the medullary substance in its composition.

The furrow that divides the two lobes of the cerebellum leads anteriorly to a process, composed of medullary and cortical substances, covered by the pia mater; and which, from its being divided into numerous furrows, resembling the rings of the earth-worm, is named processus vermiciformis. This process forms a kind of ring in its course between the lobes.

The surface of the cerebellum does not afford those circumvolutions which appear in the cerebrum; but instead of these, we observe a great number of minute furrows, running parallel to each other, and nearly in a transverse direction. The pia mater insinuates itself into these furrows.

When we cut into the substance of the cerebellum, from above downwards, we find the medullary part running in a kind of ramifying course, and exhibiting an appearance that has gotten the name of arbor vitae. These ramifications unite to form a medullary trunk; the middle, anterior, and most considerable part of which forms two processes, the crura cerebri, which unite with the crura cerebri, to form the medulla oblongata. The rest furnishes two other processes, which lose themselves, under the names, and thus unite the lobes of the cerebellum to the posterior part of the cerebrum. Under the names we observe a transverse medullary line, or linea alba, running from one of these processes to the other; and between them we find a very thin medullary lamina, covered with the pia mater, which the generality of anatomists have (though seemingly without reason) considered as a valve formed for closing the communication between the fourth ventricle.

(N) The under part of it, however, appears to be impervious; at least no injection that can be depended on has been made to pass from it into the glandula pituitaria without laceration of parts. The medulla oblongata is situated in the middle, lower, and posterior part of the cranium, and may be considered as a production or continuation of the whole medullary substance of the cerebrum and cerebellum, being formed by the union of two considerable medullary processes of the cerebrum, called crura cerebri, with two other smaller ones from the cerebellum, which were just now spoken of under the name of crura cerebelli.

The crura cerebri arise from the middle and lower part of each hemisphere. They are separated from each other at their origin, but are united below, where they terminate in a middle protuberance, the pons Varolii, so called because Varolius compared it to a bridge. This name, however, can convey no idea of its real appearance. It is, in fact, nothing more than a medullary protuberance, nearly of a hemispherical shape, which unites the crura cerebri to those of the cerebellum.

Between the crura cerebri, and near the anterior edge of the pons Varolii, are two tubercles, composed externally of medullary, and internally of ehirinoid substance, to which Eustachius first gave the name of eminentia mamillares.

Along the middle of the posterior surface of the medulla oblongata, where it forms the anterior part of the fourth ventricle, we observe a kind of furrow which runs downwards and terminates in a point. About an inch above the lower extremity of this fissure, several medullary filaments are to be seen running towards it on each side in an oblique direction, so as to give it the appearance of a writing pen; hence it is called calamus scriptorius.

From the posterior part of the pons Varolii, the medulla oblongata descends obliquely backwards; at its fore part, immediately behind the pons Varolii, we observe two pair of eminences, which were described by Eustachius, but received no particular appellation till the time of Vieussens, who gave them the names of corpora olivaria and corpora pyramidalia. The former are the outermost, being placed one on each side. They are nearly of an oval shape, and are composed of medulla, with streaks of cortical substance. Between these are the corpora pyramidalia, each of which terminates in a point. In the human subject these four eminences are sometimes not easily distinguished.

The medulla spinalis, or spinal marrow, which is the name given to the medullary chord that is extended down the vertebral canal, from the great foramen of the occipital bone to the bottom of the last lumbar vertebra, is a continuation of the medulla oblongata. Like the other parts of the brain, it is invested by the dura and pia mater. The first of these, in its passage out of the cranium, adheres to the foramen of the os occipitis. Its connection with the ligamentary substance that lines the cavity of the spine, is only by means of cellular membrane; but between the several vertebrae, where the nerves pass out of the spine, it sends off prolongations, which adhere strongly to the vertebral ligaments. Here, as in the cranium, the dura mater has its sinuses or large veins. These are two in number, and are seen running on each side of the medullary column, from the foramen magnum of the os occipitis to the lower part of the os sacrum. They communicate together by ramifying branches at each vertebra, and terminate in the vertebral, intercostal, and sacral veins.

The pia mater is connected with the dura mater by means of a thin transparent substance, which from its indentations between the spinal nerves has obtained the name of ligamentum denticulatum. It is somewhat firmer than the tunica arachnoidea, but in other respects resembles that membrane. Its use is to support the spinal marrow, that it may not affect the medulla oblongata by its weight.

The spinal marrow itself is externally of a white colour; but, upon cutting into it, we find its middle part composed of a darker-coloured mass, resembling the cortex of the brain. When the marrow has reached the first lumbar vertebra, it becomes extremely narrow, and at length terminates in an oblong protuberance; from the extremity of which the pia mater sends off a prolongation or ligament, resembling a nerve, that perforates the dura mater, and is fixed to the os coccygis.

The medulla spinalis gives rise to 30 or 31 pair of nerves, but they are not all of the same size, nor do they all run in the same direction. The upper ones are thinner than the rest, and are placed almost transversely: as we descend, we find them running more and more obliquely downwards, till at length their course is almost perpendicular, so that the lowermost nerves exhibit an appearance that is called cauda equina, from its resemblance to a horse's tail.

The arteries that ramify through the different parts of the brain are derived from the internal carotid and from the vertebral arteries. The medulla spinalis is supplied by the anterior and posterior spinal arteries, and likewise receives branches from the cervical, the inferior and superior intercostal, the lumbar, and the sacral arteries.

Sect. II. Of the Nerves.

The nerves are medullary chords, differing from each other in size, colour, and consistence, and deriving their origin from the medulla oblongata and medulla spinalis. There are 39, and sometimes 40, pair of the nerves; nine (o) of which originate from the medulla oblongata, and 30 or 31 from the medulla spinalis. They appear to be perfectly inelastic, and likewise to possess no irritability. If we irritate muscular fibres, they immediately contract; but nothing of this sort happens if we irritate a nerve. They carry with them a covering from the pia mater; but derive no tunic from the dura mater, as hath been generally, though erroneously, supposed, ever since the time of Galen.

(o) It has been usual to describe ten pair of nerves as arising from the medulla oblongata; but as the tenth pair arise in the same manner as the other spinal nerves, Santerini, Heister, Haller, and others, seem very properly to have classed them among the nerves of the spine. Galen (p), the outer covering of the nerves being in fact nothing more than cellular membrane. This covering is very thick where the nerve is exposed to the action of the muscles; but where it runs through a bony canal, or is secure from pressure, the cellular tunic is extremely thin, or altogether wanting. We have instances of this in the portio mollis of the auditory nerve, and in the nerves of the heart.

By elevating, carefully and gently, the brain from the basis of the cranium, we find the first nine pair arising in the following order: 1. The nervi olfactorii, distributed through the pituitary membrane, which constitutes the organ of smell. 2. The optici, which go to the eyes, where they receive the impressions of visible objects. 3. The oculorum motores, so called because they are distributed to the muscles of the eye. 4. The pathetici, distributed to the superior oblique muscles of the eyes, the motion of which is expressive of certain passions of the soul. 5. The nerves of this pair soon divide into three principal branches, and each of these has a different name. Its upper division is the ophthalmicus, which is distributed to various parts of the eyes, eyelids, forehead, nose, and integuments of the face. The second is called the maxillaris superior, and the third maxillaris inferior; both which names allude to their distribution. 6. The abductores; each of these nerves is distributed to the abductor muscle of the eye, so called, because it helps to draw the globe of the eye from the nose. 7. The auditorii (a), which are distributed through the organs of hearing. 8. The par vagum, which derives its name from the great number of parts to which it gives branches, both in the thorax and abdomen. 9. The linguales, or hypoglossi, which are distributed to the tongue, and appear to contribute both to the organ of taste and to the motions of the tongue (n).

It has already been observed, that the spinal marrow sends off 30 or 31 pair of nerves; these are chiefly distributed to the exterior parts of the trunk and to the extremities. They are commonly distinguished into the cervical, dorsal, lumbar, and sacral nerves. The cervical, which pass out from between the several vertebrae of the neck, are eight (s) in number; the dorsal, twelve; the lumbar, five; and the sacral, five or six; the number of the latter depending on the number of holes in the os sacrum. Each spinal nerve at its origin is composed of two fasciculi of medullary fibres. One of these fasciculi arises from the anterior, and the other from the posterior, surface of the medulla. These fasciculi are separated by the ligamentum denticulatum; after which we find them contiguous to one another. They then perforate the dura mater, and unite to form a considerable knot or ganglion. Each of these ganglions sends off two branches; one anterior, and the other posterior. The anterior branches communicate with each other at their coming out of the spine, and likewise send off one, and sometimes more branches, to assist in the formation of the intercostal nerve.

The knots or ganglions of the nerves just now spoken of, are not only to be met with at their exit from the spine, but likewise in various parts of the body. They occur in the nerves of the medulla oblongata, as well as in those of the spine. They are not the effects of disease, but are to be met with in the same parts of the same nerves, both in the fetus and adult. They are commonly of an oblong shape, and of a grayish colour somewhat inclined to red, which is perhaps owing to their being extremely vascular. Internally we are able to distinguish something like an intermixture of the nervous filaments.

Some writers have considered them as so many little brains; Lancisi fancied he had discovered muscular fibres in them, but they are certainly not of an irritable nature. A late writer, Dr Johnstone*, imagines they are intended to deprive us of the power of the will over certain parts, as the heart, for instance: but if this hypothesis were well founded, we should meet with them only in nerves leading to involuntary muscles; whereas it is certain, that the voluntary muscles receive their nerves through ganglions. Dr Monro, from observing the accurate intermixture of the minute nerves which compose them, considers them as new sources of nervous energy†.

(f) Baron Haller and Professor Zinn seem to have been the first who demonstrated, that the dura mater is reflected upon and adheres to the periosteum at the edges of the foramina that afford a passage to the nerves out of the cranium and vertebral canal, or is soon lost in the cellular substance.

(g) This pair, soon after its entrance into the meatus auditorius internus, separates into two branches. One of these is of a very soft and pulpy consistence, is called the portio mollis of the seventh pair, and is spread over the inner part of the ear. The other passes out through the aqueduct of Fallopian in a firm chord, which is distinguished as the portio dura, and is distributed to the external ear and other parts of the neck and face.

(h) Heister has summed up the uses of these nine pair of nerves in the two following Latin verses:

"Olfuciens, cornens, oculoque movens, patiensque, "Gustans, abducens, audiensque, vagansque, loquensque."

(i) Besides these, there is another pair called accessorii, which arises from the medulla spinalis at its beginning; and ascending through the great foramen of the os occipitis into the cranium, passes out again close to the eighth pair, with which, however, it does not unite; and it is afterwards distributed chiefly to the muscles of the neck, back, and scapula. In this course it sends off filaments to different parts, and likewise communicates with several other nerves. Physiologists are at a loss how to account for the singular origin and course of these nervi accessorii. The ancients considered them as branches of the eighth pair, distributed to muscles of the scapula: Willis likewise considered them as appendages to that pair, and on that account named them accessorii. They are sometimes called the spinal pair; but as this latter name is applicable to all the nerves of the spine indiscriminately, it seems better to adopt that given by Willis. The nerves, like the blood vessels, in their course through the body, communicate with each other; and each of these communications constitutes what is called a plexus, from whence branches are again detached to different parts of the body. Some of these are constant and considerable enough to be distinguished by particular names, as the semilunar plexus, the pulmonary plexus, the hepatic, the cardiac, &c.

It would be foreign to the purpose of this work to follow the nerves through all their distributions; but it may be remembered, that in describing the different viscera, mention was made of the nerves distributed to them. There is one pair, however, called the intercostal, or great sympathetic nerve, which seems to require particular notice, because it has an almost universal connexion and correspondence with all the other nerves of the body. Authors are not perfectly agreed about the origin of the intercostal; but it may perhaps not improperly be described, as beginning from filaments of the fifth and sixth pair; it then passes out of the cranium, through the bony canal of the carotid, from whence it descends laterally close to the bodies of the vertebrae, and receives branches from almost all the vertebral nerves: forming almost as many ganglions in its course through the thorax and abdomen. It sends off an infinite number of branches to the viscera in those cavities, and forms several plexus with the branches of the eighth pair or par vagum.

That the nerves are destined to convey the principles of motion and sensibility to the brain from all parts of the system, there can be no doubt; but how these effects are produced, no one has ever yet been able to determine. The inquiry has been a constant source of hypothesis in all ages, and has produced some ingenious ideas, and many erroneous positions, but without having hitherto afforded much satisfactory information.

Some physiologists have considered a trunk of nerves as a solid chord, capable of being divided into an infinite number of filaments, by means of which the impressions of feeling are conveyed to the sensorium commune. Others have supposed it to be a canal, which afterwards separates into more minute channels; or, perhaps, as being an assemblage of many very small and distinct tubes, connected to each other, and thus forming a cylindrical chord. They who contend for their being solid bodies are of opinion, that feeling is occasioned by vibration; so that, for instance, according to this system, by pricking the finger, a vibration would be occasioned in the nerve distributed though its substance; and the effects of this vibration, when extended to the sensorium, would be an excitant of pain. But the inelasticity, the softness, the connexion, and the situation of the nerves, are so many proofs that vibration has no share in the cause of feeling.

Others have supposed, that in the brain and spinal marrow a very subtle fluid is secreted, and from thence conveyed through the imperceptible tubes, which they consider as existing in the nerves. They have further supposed, that this very subtle fluid, to which they have given the name of animal spirits, is secreted in the cortical substance of the brain and spinal marrow, from whence it passes through the medullary substance. This, like the other system, is founded altogether on hypothesis; but it seems to be a hypothesis derived from much more probable principles, and there are many ingenious arguments to be brought in its support.

EXPLANATION OF PLATE XXXI.

Fig. 1. Represents the Inferior part of the Brain; —the Anterior part of the whole spine, including the Medulla Spinalis;—with the origin and large portions of all the Nerves.

AA, The anterior lobes of the cerebrum. BB, The lateral lobes of the cerebrum. CC, The two lobes of the cerebellum. DD, Tuber annulare. EE, The passage from the third ventricle to the infundibulum. FF, The medulla oblongata, which sends off the medulla spinalis through the spine. GG, That part of the os occipitis which is placed above (HH) the transverse processes of the first cervical vertebra. II, &c. The seven cervical vertebrae, with their intermediate cartilages. KK, &c. The twelve dorsal vertebrae, with their intermediate cartilages. LL, &c. The five lumbar vertebrae, with their intermediate cartilages. MM, The os sacrum. NN, The os coccygis.

Nerves.—1, The first pair of nerves, named olfactory, which goes to the nose. 2, The second pair, named optic, which goes to form the tunic retina of the eye. 3, The third pair, named motor oculi; it supplies most of the muscles of the eyeballs. 4, The fourth pair, named pathetic,—which is wholly spent upon the musculus trochlearis of the eye. 5, The fifth pair divides into three branches.—The first, named ophthalmic, goes to the orbit, supplies the lachrymal gland, and sends branches out to the forehead and nose.—The second, named superior maxillary, supplies the teeth of the upper jaw, and some of the muscles of the lips.—The third, named inferior maxillary, is spent upon the muscles and teeth of the lower jaw, tongue, and muscles of the lips. 6, The sixth pair, which, after sending off the beginning of the intercostal or great sympathetic, is spent upon the abductor oculi. 7, The seventh pair, named auditory, divides into two branches.—The largest, named portio mollis, is spent upon the internal ear.—The smallest, portio dura, joins to the fifth pair within the internal ear by a reflected branch from the second of the fifth; and within the tympanum, by a branch from the third of the fifth, named chorda tympani.—Vid. fig. 3. near B. 8, The eighth pair, named par vagum,—which accompanies the intercostal, and is spent upon the tongue, larynx, pharynx, lungs, and abdominal viscera. 9, The ninth pair, which are spent upon the tongue. 10, The intercostal, or great sympathetic, which is seen from the sixth pair to the bottom of the pelvis on each side of the spine, and joining with all the nerves of the spine; in its progress supplying the heart, and, with the par vagum, the contents of the abdomen and pelvis. 11, The accessorius, which is spent upon the sternocleido-mastoides and trapezius muscles. muscles. 12 12, The first cervical nerves; 13 13, The second cervical nerves; both spent upon the muscles that lie on the neck, and teguments of the neck and head. 14 14, The third cervical nerves, which, after sending off (15 15, &c.) the phrenic nerves to the diaphragm, supply the muscles and tegments that lie on the side of the neck, and top of the shoulder. 16 16, The brachial plexus, formed by the fourth, fifth, sixth, seventh cervicals, and first dorsal nerves,—which supply the muscles, and tegments of the superior extremity. 17 17, The twelve dorsal, or proper intercostal nerves, which are spent upon the intercostal muscles and some of the large muscles which lie upon the thorax. 18 18, The five lumbar pairs of nerves which supply the lumbar and abdominal muscles, and some of the tegments and muscles of the inferior extremity. 19 19, The sacro-sciatic, or posterior crural nerve, formed by the two inferior lumbar, and three superior of the os sacrum. This large nerve supplies the greatest part of the muscles and tegments of the inferior extremity. 20, The stomachic plexus, formed by the eighth pair. 21 21, Branches of the solar or celiac plexus, formed by the eighth pair and intercostals, which supply the stomach and chylopoietic viscera. 22 22, Branches of the superior and inferior mesenteric plexuses, formed by the eighth pair and intercostals, which supply the chylopoietic viscera, with part of the organs of urine and generation. 23 23, Nerves which accompany the spermatic chord. 24 24, The hypogastric plexus, which supplies the organs of urine and generation within the pelvis.

Fig. 2, 3, 4, 5. Show different views of the Inferior part of the Brain, cut perpendicularly through the Middle—with the Origin and large portions of all the Nerves which pass out through the Bones of the Cranium,—and the three first Cervicals.

A, The anterior lobe. B, The lateral lobe of the cerebrum. C, One of the lobes of the cerebellum. D, Tuber annulare. E, Corpus pyramidale, in the middle of the medulla oblongata. F, The corpus olivare, in the side of the medulla oblongata. G, The medulla oblongata. H, The medulla spinalis.

Nerves.—1 2 3 4 5 6 7 8 and 9, Pairs of nerves. 10 10, Nervus accessorius, which comes from—11, 12, and 13, the three cervical nerves.

CHAP. VI. OF THE SENSES, AND THEIR ORGANS.

In treating of the senses, we mean to confine ourselves to the external ones of touch, taste, smelling, hearing, and vision. The word sense, when applied to these five, seems to imply not only the sensation excited in the mind by certain impressions made on the body, but likewise the organs destined to receive and transmit these impressions to the sensorium. Each of these organs being of a peculiar structure, is susceptible only of particular impressions, which will be pointed out as we proceed to describe each of them separately.

SECT. I. Of Touch.

The sense of touch may be defined to be the faculty of distinguishing certain properties of bodies by the feel. In a general acceptation, this definition might perhaps not improperly be extended to every part of the body possessed of sensibility (x); but it is commonly confined to the nervous papillae of the cutis, or true skin, which, with its appendages, and their several uses, have been already described.

The exterior properties of bodies, such as their solidity, moisture, inequality, smoothness, dryness or fluidity, and likewise their degree of heat, seem all to be capable of making different impressions on the papillae, and consequently of exciting different ideas in the sensorium commune. But the organ of touch, like all the other senses, is not equally delicate in every part of the body, or in every subject; being in some much more exquisite than it is in others.

SECT. II. Of Taste.

The sense of taste is seated chiefly in the tongue; the situation and figure of which are sufficiently known.

On the upper surface of this organ we may observe a great number of papillae, which, on account of their difference in size and shape, are commonly divided into three classes. The largest are situated towards the basis of the tongue. Their number commonly varies from seven to nine, and they seem to be mucous follicles. Those of the second class are somewhat smaller, and of a cylindrical shape. They are most numerous about the middle of the tongue. Those of the third class are very minute, and of a conical shape. They are

(x) In the course of this article, mention has often been made of the sensibility or insensibility of different parts of the body; it will therefore, perhaps, not be amiss to observe in this place, that many parts which were formerly supposed to possess the most exquisite sense, are now known to have but little or no feeling, at least in a sound state; for in an inflamed state, even the bones, the most insensible parts of any, become susceptible of the most painful sensations. This curious discovery is due to the late Baron Haller. His experiments prove, that the bones, cartilages, ligaments, tendons, epidermis, and membranes (as the pleura, pericardium, dura and pia mater, periosteum, &c.) may in a healthy state be considered as insensible. As sensibility depends on the brain and nerves, of course different parts will possess a greater or less degree of feeling, in proportion as they are supplied with a greater or smaller number of nerves. Upon this principle it is, that the skin, muscles, stomach, intestines, urinary bladder, ureters, uterus, vagina, penis, tongue, and retina, are extremely sensible, while the lungs and glands have only an obscure degree of feeling. are very numerous on the apex and edges of the tongue, and have been supposed to be formed by the extremities of its nerves.

We observe a line, the linea linguae mediana, running along the middle of the tongue, and dividing it as it were into two portions. Towards the basis of the tongue, we meet with a little cavity, named by Morgagni foramen cæcum, which seems to be nothing more than a common termination of some of the excretory ducts of mucous glands situated within the substance of the tongue.

We have already observed, that this organ is everywhere covered by the cuticle, which, by forming a reduplication, called the frenum, at its under part, serves to prevent the too great motion of the tongue, and to fix it in its situation. But, besides this attachment, the tongue is connected, by means of its muscles and membranous ligaments, to the lower jaw, the os hyoides, and the styloid processes.

The principal arteries of the tongue are the linguales, which arise from the external carotid. Its veins empty themselves into the external jugulars. Its nerves arise from the fifth, eighth, and ninth pair.

The variety of tastes seems to be occasioned by the different impressions made on the papillae by the food. The different state of the papillae with respect to their moisture, their figure, or their covering, seems to produce a considerable difference in the taste, not only in different people, but in the same subject, in sickness and in health. The great use of the taste seems to be to enable us to distinguish wholesome and salutary food from that which is unhealthy; and we observe that many quadrupeds, by having their papillae (u) very large and long, have the faculty of distinguishing flavours with infinite accuracy.

Sect. III. Of Smelling.

The sense of smelling, like the sense of taste, seems intended to direct us to a proper choice of aliment, and is chiefly seated in the nose, which is distinguished into its external and internal parts. The situation and figure of the former of these do not seem to require a definition. It is composed of bones and cartilages, covered by muscular fibres and by the common integuments. The bones make up the upper portion, and the cartilages the lower one. The septum narium, like the nose, is likewise in part bony, and in part cartilaginous. These bones and their connexions were described in the osteology.

The internal part of the nose, besides the osa spongiosa, has six cavities or sinuses, the maxillary, the frontal, and the sphenoid, which were all described with the bones of the head. They all open into the nostrils; and the nose likewise communicates with the mouth, larynx, and pharynx, posteriorly behind the velum palati.

All these several parts, which are included in the internal division of the nose, viz. the inner surface of the nostrils, the lamellae of the osa spongiosa and the sinus-

(u) Malpighi's description of the papillae, which has been copied by many anatomical writers, seems to have been taken chiefly from the tongues of sheep.

Sect. IV. Of Hearing.

Before we undertake to explain the manner in which we are enabled to receive the impressions of sound, it will be necessary to describe the ear, which is the organ of hearing. It is commonly distinguished into external and internal. The former of these divisions includes all that we are able to discover without dissection, and the meatus auditorius, as far as the tympanum; and the latter, all the other parts of the ear.

The external ear is a cartilaginous funnel, covered by the common integuments, and attached, by means of its ligaments and muscles, to the temporal bone. Although... Although capable only of a very obscure motion, it is found to have several muscles. Different parts of it are distinguished by different names; all its cartilaginous part is called ala or wing, to distinguish it from the soft and pendant part below, called the lobe. Its outer circle or border is called helix, and the semicircle within this, antihelix. The moveable cartilage placed immediately before the meatus auditorius, which it may be made to close exactly, is named tragus; and an eminence opposite to this, at the extremity of the antihelix, is called antitragus. The concha is a considerable cavity formed by the extremities of the helix and antihelix. The meatus auditorius, which at its opening is cartilaginous, is lined with a very thin membrane, which is a continuation of the cuticle from the surface of the ear.

In this canal we find a yellow wax, which is secreted by a number of minute glands or follicles, each of which has an excretory duct. The secretion, which is at first of an oily consistence, defends the membrane of the tympanum from the injuries of the air; and, by its bitterness, prevents minute insects from entering into the ear. But when from neglect or disease it accumulates in too great a quantity, it sometimes occasions deafness. The inner extremity of the meatus is closed by a very thin transparent membrane, the membrana tympani, which is set in a bony circle like the head of a drum. In the last century Rivinus, professor at Leipzig, fancied he had discovered a hole in this membrane, surrounded by a sphincter, and affording a passage to the air, between the external and internal ear. Cowper, Heister, and some other anatomists, have admitted this supposed foramen, which certainly does not exist. Whenever there is any opening in the membrana tympani, it may be considered as accidental. Under the membrana tympani runs a branch of the fifth pair of nerves, called chorda tympani; and beyond this membrane is the cavity of the tympanum, which is about seven or eight lines wide, and half so many in depth; it is semispherical, and everywhere lined by a very fine membrane. There are four openings to be observed in this cavity. It communicates with the mouth by means of the Eustachian tube. This canal, which is in part bony and in part cartilaginous, begins by a very narrow opening at the anterior and almost superior part of the tympanum, increasing in size as it advances towards the palate of the mouth, where it terminates by an oval opening. This tube is everywhere lined by the same membrane that covers the inside of the mouth. The real use of this canal does not seem to have been hitherto satisfactorily ascertained; but sound would seem to be conveyed through it to the membrana tympani, deaf persons being often observed to listen attentively with their mouths open. Opposite to this is a minute passage, which leads to the sinuosities of the mastoid process; and the other two openings, which are in the internal process of the os petrosum, are the fenestra ovalis, and fenestra rotunda, both of which are covered by a very fine membrane.

There are three distinct bones in the cavity of the tympanum; and these are the malleus, incus, and stapes. Besides these there is a fourth, which is the os orbiculare, considered by some anatomists as a process of the stapes, which is necessarily broken off by the violence we are obliged to use in getting at these bones; but when accurately considered, it seems to be a distinct bone.

The malleus is supposed to resemble a hammer, being larger at one extremity, which is its head, than it is at the other, which is its handle. The latter is attached to the membrana tympani, and the head of the bone is articulated with the incus.

The incus, as it is called from its shape, though it seems to have less resemblance to an anvil than to one of the dentes molares with its roots widely separated from each other, is distinguished into its body and its legs. One of its legs is placed at the entry of the canal which leads to the mastoid process; and the other, which is somewhat longer, is articulated with the stapes, or rather with the os orbiculare, which is placed between them.

The third bone is very properly named stapes, being perfectly shaped like a stirrup. Its basis is fixed into the fenestra ovalis, and its upper part is articulated with the os orbiculare. What is called the fenestra rotunda, though perhaps improperly, as it is more oval than round, is observed a little above the other, in an eminence formed by the os petrosum, and is closed by a continuation of the membrane that lines the inner surface of the tympanum. The stapes and malleus are each of them furnished with a little muscle, the stapedius and tensor tympani. The first of these, which is the smallest in the body, arises from a little cavern in the posterior and upper part of the cavity of the tympanum; and its tendon, after passing through a hole in the same cavern, is inserted at the back part of the head of the stapes. This muscle, by drawing the stapes obliquely upwards, assists in stretching the membrana tympani.

The tensor tympani (x), or internus mallei as it is called by some writers, arises from the cartilaginous extremity of the Eustachian tube, and is inserted into the back part of the handle of the malleus, which it serves to pull upwards, and of course helps to stretch the membrana tympani.

The labyrinth is the only part of the ear which remains to be described. It is situated in the os petrosum, and is separated from the tympanum by a partition which is everywhere bony, except at the two fenestrae. It is composed of three parts; and these are the vestibulum, the semicircular canals, and the cochlea.

The vestibulum is an irregular cavity, much smaller than the tympanum, situated nearly in the centre of the os petrosum, between the tympanum, the cochlea, and the semicircular canals. It is open on the side of the tympanum by means of the fenestra ovalis, and communicates with the upper portion of the cochlea by an oblong

(x) Some anatomists describe three muscles of the malleus; but only this one seems to deserve the name of muscle; what are called the externus and obliquus mallei seeming to be ligaments rather than muscles. oblong foramen, which is under the fenestra ovalis, from which it is separated only by a very thin partition.

Each of the three semicircular canals forms about half a circle of nearly a line in diameter, and running each in a different direction, they are distinguished into vertical, oblique, and horizontal. These three canals open by both their extremities into the vestibulum; but the vertical and the oblique being united together at one of their extremities, there are only five orifices to be seen in the vestibulum.

The cochlea is a canal which takes a spiral course, not unlike the shell of a snail. From its basis to its apex it makes two turns and a half; and is divided into two canals by a very thin lamina or septum, which is in part bony and in part membranous, in such a manner that these two canals only communicate with each other at the point. One of them opens into the vestibulum, and the other is covered by the membrane that closes the fenestra rotunda. The bony lamella which separates the two canals is exceedingly thin, and fills about two-thirds of the diameter of the canal. The rest of the septum is composed of a most delicate membrane, which lines the whole inner surface of the cochlea, and seems to form this division in the same manner as the two membranous bags of the pleura, by being applied to each other, form the mediastinum.

Every part of the labyrinth is furnished with a very delicate periosteum, and filled with a watery fluid, secreted as in other cavities. This fluid transmits to the nerves the vibrations it receives from the membrane closing the fenestra rotunda, and from the basis of the stapes, where it rests on the fenestrum ovale. When this fluid is collected in too great a quantity, or is compressed by the stapes, it is supposed to escape through two minute canals or aqueducts, lately described by Dr Cotunni*, an ingenious physician at Naples. One of these aqueducts opens into the bottom of the vestibulum, and the other into the cochlea, near the fenestra rotunda. They both pass through the os petrosum, and communicate with the cavity of the cranium where the fluid that passes through them is absorbed; and they are lined by a membrane which is supposed to be a production of the dura mater.

The arteries of the external ear come from the temporal and other branches of the external carotid, and its veins pass into the jugular. The internal ear receives branches of arteries from the basilar and carotids, and its veins empty themselves into the sinuses of the dura mater, and into the internal jugular.

The portio mollis of the seventh pair is distributed through the cochlea, the vestibulum, and the semicircular canals; and the portio dura sends off a branch to the tympanum, and other branches to the external ear and parts near it.

The sense of hearing, in producing which all the parts we have described assist, is occasioned by a certain modulation of the air collected by the funnel-like shape of the external ear, and conveyed through the meatus auditorius to the membrana tympani. That sound is propagated by means of the air, is very easily proved by ringing a bell under the receiver of an air-pump; the sound it affords being found to diminish gradually as the air becomes exhausted, till at length it ceases to be heard at all. Sound moves through the air with infinite velocity; but the degree of its motion seems to depend on the state of the air, as it constantly moves faster in a dense and dry, than it does in a moist and rarefied air.

That the air vibrating on the membrana tympani communicates its vibration to the different parts of the labyrinth, and by means of the fluid contained in this cavity affects the auditory nerve so as to produce sound, seems to be very probable; but the situation, the minuteness, and the variety of the parts which compose the ear, do not permit much to be advanced with certainty concerning their mode of action.

Some of these parts seem to constitute the immediate organ of hearing, and these are all the parts of the vestibulum; but there are others which seem intended for the perfection of this sense, without being absolutely essential to it. It has happened, for instance, that the membrana tympani, and the little bones of the ear, have been destroyed by disease, without depriving the patient of the sense of hearing (y).

Sound is more or less loud in proportion to the strength of the vibration; and the variety of sounds seems to depend on the difference of this vibration; for the more quick and frequent it is, the more acute will be the sound, and vice versa.

Before we conclude this article, it will be right to explain certain phenomena, which will be found to have a relation to the organ of hearing.

Every body has, in consequence of particular sounds, occasionally felt that disagreeable sensation which is usually called setting the teeth on edge: and the cause of this sensation may be traced to the communication which the portio dura of the auditory nerve has with the branches of the fifth pair that are distributed to the teeth, being probably occasioned by the violent tremor produced in the membrana tympani by these very acute sounds. Upon the same principle we may explain the strong idea of sound which a person has who holds a vibrating string between his teeth.

The humming which is sometimes perceived in the ear, without any exterior cause, may be occasioned either by an increased action of the arteries in the ears, or by convulsive contractions of the muscles of the malleus and stapes, affecting the auditory nerve in such a manner as to produce the idea of sound. An ingenious philosophical writer* has lately discovered, that there are sounds liable to be excited in the ear by irritation, and without any assistance from the vibrations of the air.

(y) This observation has led to a supposition, that a perforation of this membrane may in some cases of deafness be useful; and Mr Cheselden relates, that some years ago, a malefactor was pardoned, on condition that he should submit to this operation; but the public clamour raised against it was so great, that it was thought right not to perform it. Sect. V. Of Vision.

The eyes, which constitute the organ of vision, are situated in two bony cavities named orbits, where they are surrounded by several parts, which are either intended to protect them from external injury, or to assist in their motion.

The globe of the eye is immediately covered by two eyelids or palpebrae, which are composed of muscular fibres, covered by the common integuments, and lined by a very fine and smooth membrane, which is from thence extended over part of the globe of the eye, and is called tunica conjunctiva. Each eyelid is cartilaginous at its edge; and this border, which is called tarsus, is furnished with a row of hairs named cilia or eyelashes.

The cilia serve to protect the eye from insects and minute bodies floating in the air, and likewise to moderate the action of the rays of light in their passage to the retina. At the roots of these hairs there are sebaceous follicles, first noticed by Meibomius, which discharge a glutinous liniment. Sometimes the fluid they secrete has too much viscosity, and the eyelids become glued to each other.

The upper border of the orbit is covered by the eyebrows or supercilium, which by means of their two muscles are capable of being brought towards each other, or of being carried upwards. They have been considered as serving to protect the eyes, but they are probably intended more for ornament than utility (z).

The orbits, in which the eyes are placed, are furnished with a good deal of fat, which affords a soft bed on which the eye performs its several motions. The inner angle of each orbit, or that part of it which is near the nose, is called canthus major, or the great angle; and the outer angle, which is on the opposite side of the eye, is the canthus minor, or little angle.

The little reddish body which we observe in the great angle of the eyelids, and which is called caruncula lachrymalis, is supposed to be of a glandular structure, and, like the follicles of the eyelids, to secrete an oily humour. But its structure and use do not seem to have been hitherto accurately determined. The surface of the eye is constantly moistened by a very fine limpid fluid called the tears, which is chiefly, and perhaps wholly, derived from a large gland of the conglomerate kind, situated in a small depression of the os frontis near the outer angle of the eye. Its excretory ducts pierce the tunica conjunctiva just above the cartilaginous borders of the upper eyelids. When the tears were supposed to be secreted by the caruncle, this gland was called glandula inominata; but now that its structure and uses are ascertained, it very properly has the name of glandula lachrymalis. The tears pour out of the ducts of this gland are, in a natural and healthy state, incessantly spread over the surface of the eye, to keep it clear and transparent by means of the eyelids, and as constantly pass out at the opposite corner of the eye or inner angle, through two minute orifices, the puncta lachrymalia (A); being determined into these little openings by a reduplication of the tunica conjunctiva, shaped like a crescent, the two points of which answer to the puncta. This reduplication is named membrana or calcula semilunaris. Each of these puncta is the beginning of a small excretory tube, through which the tears pass into a little pouch or reservoir, the sacculus lachrymalis, which lies in an excavation formed partly by the nasal process of the os maxillare superius, and partly by the os unguis. The lower part of this sac forms a duct called the ductus ad nares, which is continued through a bony channel, and opens into the nose, through which the tears are occasionally discharged (B).

The motions of the eye are performed by six muscles; four of which are straight and two oblique. The straight muscles are distinguished by the names of elevator, depressor, adductor, and abductor, from their several uses in elevating and depressing the eye, drawing it towards the nose, or carrying it from the nose towards the temple. All these four muscles arise from the bottom of the orbit, and are inserted by flat tendons into the globe of the eye. The oblique muscles are intended for the more compound motions of the eye. The first of these muscles, the obliquus superior, does not, like the other four muscles we have described, arise from the bottom of the orbit, but from the edge of the foramen that transmits the optic nerve, which separates the origin of this muscle from that of the others. From this beginning it passes in a straight line towards a very small cartilaginous ring, the situation of which is marked in the skeleton by a little hollow in the internal orbital processes of the os frontis. The tendon of the muscle, after passing through this ring, is inserted into the upper part of the globe of the eye, which it serves to draw forwards, at the same time turning the pupil downwards.

The obliquus inferior arises from the edge of the orbit, under the opening of the ductus lachrymalis; and is inserted somewhat posteriorly into the outer side of the globe, serving to draw the eye forwards and turn the pupil upwards. When either of these two muscles act separately, the eye is moved on its axis; but when they act together, it is compressed both above and below. The eye itself, which is now to be described, with its tunics, humours, and component parts, is nearly of a spherical figure. Of its tunics, the conjunctiva has been already described as a partial covering, reflected from the inner surface of the eyelids over the anterior portion of the eye. What has been named

(z) It is observable, that the eyebrows are peculiar to the human species.

(A) It sometimes happens, that this very pellucid fluid, which moistens the eye, being poured out through the excretory ducts of the lachrymal gland faster than it can be carried off through the puncta, trickles down the cheek, and is then strictly and properly called tears.

(B) When the ductus ad nares becomes obstructed in consequence of disease, the tears are no longer able to pass into the nostrils; the sacculus lachrymalis becomes distended; and inflammation, and sometimes ulceration, taking place, constitute the disease called fistula lachrymalis. named albucinea cannot properly be considered as a coat of the eye, being in fact nothing more than the tendons of the straight muscles spread over some parts of the sclerotica.

The immediate tunics of the eye, which are to be demonstrated, when its partial coverings, and all the other parts with which it is surrounded, are removed, are the sclerotica, cornea, choroides, and retina.

The sclerotica, which is the exterior coat, is everywhere white and opaque, and is joined at its anterior edge to another, which has more convexity than any other part of the globe, and being exceedingly transparent is called cornea (c). These two parts are perfectly different in their structure; so that some anatomists suppose them to be as distinct from each other as the glass of a watch is from the case into which it is fixed. The sclerotica is of a compact fibrous structure; the cornea, on the other hand, is composed of a great number of laminae united by cellular membrane. By macerating them in boiling water, they do not separate from each other, as some writers have asserted; but the cornea soon softens, and becomes of a glutinous consistence.

The ancients supposed the sclerotica to be a continuation of the dura mater. Morgagni and some other modern writers are of the same opinion; but this point is disputed by Winslow, Haller, Zinn, and others. The truth seems to be, that the sclerotica, though not a production of the dura mater, adheres intimately to that membrane.

The choroides is so called because it is furnished with a great number of vessels. It has likewise been named uvea, on account of its resemblance to a grape. Many modern anatomical writers have considered it as a production of the pia mater. This was likewise the opinion of the ancients; but the strength and thickness of the choroides, when compared with the delicate structure of the pia mater, are sufficient proofs of their being two distinct membranes.

The choroides has of late generally been described as consisting of two laminae; the innermost of which has been named after Ruysch, who first described it. It is certain, however, that Ruysch's distinction is ill founded, at least with respect to the human eye, in which we are unable to demonstrate any such structure, although the tunica choroides of sheep and some other quadrupeds may easily be separated into two layers.

The choroides adheres intimately to the sclerotica round the edge of the cornea; and at the place of this union we may observe a little whitish arcæa, named ligamentum ciliare, though it is not of a ligamentous nature.

They who suppose the choroides to be composed of two laminae, describe the external one as terminating in the ligamentum ciliare, and the external one as extending farther to form the iris, which is the circle we are able to distinguish through the cornea; but this part is of a very different structure from the choroides; so that some late writers have perhaps not improperly considered the iris as a distinct membrane. It derives its name from the variety of its colours, and is perforated in its middle. This perforation, which is called the pupil or sight of the eye, is closed in the fetus by a very thin vascular membrane. This membrana pupillaris commonly disappears about the seventh month.

On the under sides of the iris, we observe many minute fibres, called ciliary processes, which pass in radii or parallel lines from the circumference to the centre. The contraction and dilatation of the pupil are supposed to depend on the action of these processes. Some have considered them as muscular, but they are not of an irritable nature; others have supposed them to be filaments of nerves; but their real structure has never yet been clearly ascertained.

Besides these ciliary processes, anatomists usually speak of the circular fibres of the iris, but no such seem to exist.

The posterior surface of the iris, the ciliary processes, and part of the tunica choroides, are covered with a black mucus for the purposes of accurate and distinct vision; but the manner in which it is secreted has not been determined.

Immediately under the tunica choroides we find the third and inner coat, called the retina, which seems to be merely an expansion of the pulpy substance of the optic nerve, extending to the borders of the crystalline humour.

The greatest part of the globe of the eye, within these several tunics, is filled by a very transparent and gelatinous humour of considerable consistence, which from its supposed resemblance to fused glass, is called the vitreous humour. It is invested by a very fine and delicate membrane, called tunica vitrea, and sometimes arachnoides.—It is supposed to be composed of two laminae; one of which dips into its substance, and by dividing the humour into cells adds to its firmness. The fore part of the vitreous humour is a little hollowed, to receive a very white and transparent substance of a firm texture, and of a lenticular and somewhat convex shape, named the crystalline humour. It is included in a capsule, which seems to be formed by a separation of the two laminae of the tunica vitrea.

The fore part of the eye is filled by a very thin and transparent fluid, named the aqueous humour, which occupies all the space between the crystalline and the prominent cornea.—The part of the choroides which is called the iris, and which comes forward to form the pupil, appears to be suspended as it were in this humour, and has occasioned this portion of the eye to be distinguished into two parts. One of these, which is the little space between the anterior surface of the crystalline and the iris, is called the posterior chamber; and the other, which is the space between the iris and the cornea, is called the anterior chamber of the eye (d).

(c) Some writers, who have given the name of cornea to all this outer coat, have named what is here and most commonly called sclerotica, cornea opaca; and its anterior and transparent portion, cornea lucida.

(d) We are aware that some anatomists, particularly Lieutaud, are of opinion, that the iris is everywhere in close contact with the crystalline, and that it is of course right to speak only of one chamber of the eye; but as Both these spaces are completely filled with the aqueous humour (E).

The eye receives its arteries from the internal carotid, through the foramina optica; and its veins pass through the foramina lacera, and empty themselves into the lateral sinuses. Some of the ramifications of these vessels appear on the inner surface of the iris, where they are seen to make very minute convolutions, which are sufficiently remarkable to be distinguished by the name of circulus arteriosus, though perhaps improperly, as they are chiefly branches of veins.

The optic nerve passes in at the posterior part of the eye, in a considerable trunk, to be expanded for the purposes of vision, of which it is now universally supposed to be the immediate seat. But Messrs Mariotte and Mery contended, that the choroides is the seat of this sense; and the ancients supposed the crystalline to be so. Besides the optic, the eye receives branches from the third, fourth, fifth, and sixth pair of nerves.

The humours of the eye, together with the cornea, are calculated to refract and converge the rays of light in such a manner as to form at the bottom of the eye a distinct image of the object we look at; and the point where the rays meet is called the focus of the eye. On the retina, as in a camera obscura, the object is painted in an inverted position; and it is only by habit that we are enabled to judge of its true situation, and likewise of its distance and magnitude. To a young gentleman who was born blind, and who was couched by Mr Cheselden, every object (as he expressed himself) seemed to touch his eyes, as what he felt did his skin; and he thought no objects so agreeable as those which were smooth and regular, although for some time he could form no judgment of their shape, or guess what it was in any of them that was pleasing to him.

In order to paint objects distinctly on the retina, the cornea is required to have such a degree of convexity, that the rays of light may be collected at a certain point, so as to terminate exactly on the retina.—If the cornea is too prominent, the rays, by diverging too soon, will be united before they reach the retina, as is the case with near-sighted people or myopes; and, on the contrary, if it is not sufficiently convex, the rays will not be perfectly united when they reach the back part of the eye; and this happens to long-sighted people or presbi, being found constantly to take place as we approach to old age, when the eye gradually flattens (E). These defects are to be supplied by means of glasses. He who has too prominent an eye, will find his vision improved by means of a concave glass; and upon the same principles, a convex glass will be found useful to a person whose eye is naturally too flat.

EXPLANATION OF PLATE XXXII.

Fig. 1. Shows the Lachrymal Canals, after the Common Teguments and Bones have been cut away. a, The lachrymal gland. b, The two puncta lachrymalia, from which the two lachrymal canals proceed to c, the lachrymal sac. d, The large lachrymal duct. e, Its opening into the nose. f, The caruncula lachrymalis. g, The eyeball.

Fig. 2. An Interior View of the Coats and Humours of the Eye. aaaan, The tunica sclerotica cut in four angles, and turned back. bbbb, The tunica choroides adhering to the inside of the sclerotic, and the ciliary vessels are seen passing over—cc, The retina, which covers the vitreous humour. dd, The ciliary processes, which were continued from the choroid coat. ee, The iris. f, The pupil.

Fig. 3. Shows the Optic Nerves, and Muscles of the Eye. aa, The two optic nerves before they meet. b, The two optic nerves conjoined. c, The right optic nerve. d, Musculus attollens palpebræ superioris. e, Attollens oculi. f, Adductor. gg, Obliquus superior, or trochlearis. h, Adductor. i, The eyeball.

Fig. 4. Shows the Eyeball with its Muscles. a, The optic nerve. b, Musculus trochlearis. c, Part of the os frontis, to which the trochlear or pulley is fixed, through which,—d, The tendons of the trochlearis pass. e, Attollens oculi. f, Adductor oculi. g, Adductor oculi. h, Obliquus inferior. i, Part of the superior maxillary bone to which it is fixed. k, The eyeball.

Fig. 5. Represents the Nerves and Muscles of the Right Eye, after part of the Bones of the Orbit have been cut away. A, The eyeball. B, The lachrymal gland. C, Musculus adductor oculi. D, Attollens. E, Levator palpebræ superioris. F, Depressor oculi. G, Adductor. H, Obliquus superior, with its pulley. I, Its insertion into the sclerotic coat. K, Part of the obliquus inferior. L, The anterior part of the os frontis cut.

This does not appear to be the case, the situation of the iris and the two chambers of the eye are here described in the usual way.

(E) When the crystalline becomes opaque, so as to prevent the passage of the rays of light to the retina, it constitutes what is called a cataract; and the operation of couching consists in removing the diseased crystalline from its bed in the vitreous humour. In this operation the cornea is perforated, and the aqueous humour escapes out of the eye, but it is constantly renewed again in a very short time. The manner, however, in which it is secreted has not yet been determined.

(F) Upon this principle, they, who in their youth are near-sighted, may expect to see better as they advance in life, as their eyes gradually become more flat. HAVING fully examined and described the structure of man, we are now to take a view of that of the inferior animals, and to consider in what the rest of animated nature differs from man.

Comparative anatomy was formerly, as we have shewn in the history, much more cultivated than that of the human body; but when the prejudices of bigotry and ignorance subsided, and allowed human dissection to be more freely exercised, the study of this species of anatomy was almost entirely neglected. Of late, however, it has attracted the attention of several of the most eminent naturalists and anatomists, particularly of Monro, Hunter, Vieq d'Azyr, and Cuvier, from whose labours it has received considerable improvement, and has attained a degree of accuracy and an extent of application, which render it an object of inquiry highly interesting to the philosopher and the physician.

Many advantages are derived from the study of comparative anatomy. First, It furnishes us with a sufficient knowledge of the several parts of animals, to prevent our being imposed on by those authors who have described and delineated many organs from brutes as belonging to the human body. That this is of importance, is evinced by examining the works of some of the earliest and greatest masters of anatomy, who, for want of human subjects, have often taken their descriptions from other animals; Galen is notoriously faulty in this respect, and the great Vesalius, though he justly reproved Galen, has fallen into the same error, as is plain from his delineations of the kidneys, the uterus, the muscles of the eye, and other parts. Nor is antiquity only chargeable with this, since in Willis's *Anatomia Cerebri* (the plates of which were revised by that accurate anatomist Dr Lower) there are several of the figures taken from different brutes, especially from the dog, besides what he acknowledges for such.

Secondly, It helps us to understand several passages in the ancient writers on medicine, especially Hippocrates and Galen, who have taken many of their descriptions from brutes, and reasoned from them.

Thirdly, It affords one of the best assistants and most certain guides in the study of natural history; and the Fourthly, From comparing the organization of man with that of other animals, we derive considerable aid in our physiological researches, as many functions of the animal economy can be but imperfectly understood, without comparing in various classes the organs which are subservient to them. From a want of this comparative view, there have arisen among anatomists many disputes, which a more enlarged acquaintance with this subject has decided.

To these advantages of comparative anatomy, we may add, that it may be practised at all times and in all places; and this enables those, who from prejudice or delicacy, are withheld from the study of anatomy on the human subject, to acquire at an easy rate a knowledge of this useful science, sufficient for the usual purposes of a liberal education.

CHAP. I. GENERAL VARIATIONS IN THE ORGANIZATION AND FUNCTIONS.

THE most obvious and simple function of an animal is motion, and we therefore begin with the organs by which this is produced. All animals are furnished with muscles, or muscular fibres, but a great proportion of them have nothing analogous to bone. In those which have bones, there are two striking distinctions; in one division they are situated within the muscles, forming an internal articulated skeleton; in the other they form an external scaly or shelly covering, within which the muscles are included.

Those animals which are furnished with articulated skeletons, and constituting what is called a vertebral column, are denominated vertebral animals. Of these there are four orders, the mammalia, birds, fishes, and reptiles. All other animals, comprehending the mollusca, insects, worms, and zoophytes, may be called invertebral animals.

The general differences in the organs of sensation are much less simple; they may be considered as respecting the internal nervous system, and the organs of the external senses. With respect to the former, some animals appear to have no nervous system, as the zoophytes; another class has all of this internal system except the brain, situated in the same cavity with the viscera, as the mollusca, insects, and some of the articulated worms; the third and most complete class, have the common origin of the nerves situated in a cavity, distinct from that of the viscera, within the vertebral column; this comprehends all the vertebral animals.

The two first classes have the ganglia or nervous knots, (Vid. Ganglia, Anatomy) forming protuberances in the general nervous cord, as is the case with insects and some articulated worms; or have them only within the larger cavities, as the mollusca: the last division have them either on the sides of the cord, or within the cavities, or both.

The external senses differ in number and energy. All the vertebral animals agree with man in having five senses. Of the invertebral animals, all appear to possess smell, taste, and feeling; most of the mollusca and insects, as far as is yet known, are without hearing; and the mollusca who want heads, the larvae of some insects, many of the articulated worms, and all the zoophytes, are not possessed of sight. The energy of the senses varies very considerably in different classes, and in different individuals; some, as most of the dogs, the vulture, and most of the sarcophagy, or animals which prey on carrion, have the sense of smelling extremely acute, and in these the membrane lining the nasal cavities appears to be proportionally more extended than in others. Some excel in the sense of feeling, particularly man and the monkey tribe, in whom the extremities are most divided, most delicate, and furnished with the most minute ramifications of the superficial nerves. Man, and those animals who, like man, have the power of moving the head in all directions, possess a great extent of vision, both as to circuit and distance; and these have two eyes sunk and fixed within the head; others, as most insects, which are to see minute objects near at hand, have either several eyes, or at least eyes containing several lenses. But the differences which appear in these organs will be fully noticed in comparing the several classes.

The organs of digestion furnish us with two great distinctions. Some animals, as most of the zoophytes, have only one opening to the alimentary canal, which serves both for the taking in of aliment, and the rejection of the excrement; in all others this canal has two distinct openings, at a greater or less distance from each other, according as the convolutions of this canal are more or less numerous. Another difference which has a considerable influence on the nature of the aliment, adapted to the several species is, that some animals have the mouth furnished with teeth or other hard bodies for the purpose of breaking down solids, and that others want these organs. In the latter case, the animal, if its mouth be large, can swallow its food entire, or if its mouth be in the form of a tube, can only suck in fluid substances. The nature of the bodies which the animal is to masticate, is also influenced by the form of the teeth: thus some animals have only teeth formed for cutting and tearing, and therefore can only subsist on flesh, or are carnivorous; others have chiefly grinding teeth, calculated only for bruising herbs and grain, and these are herbivorous; a third class have both, and variations, are omnivorous. The difference of aliment is attended with a correspondent difference in the structure of the alimentary canal, as to its greater or smaller length, the number of stomachs, &c.

The chyle formed from the aliment by the action of these organs, is carried to its place of destination in one of two ways; it either exudes through the sides of the alimentary canal, or it is absorbed by particular vessels, by which it is conveyed into the general circulation. The former takes place in the zoophytes, and according to Cuvier in most insects, which appear to possess no proper circulating vessels. The latter is the case in the mollusca, and in all the vertebral animals; but these have the blood red and the chyle white, while those have all the fluids of the same whitish colour. Of the vertebral animals too, the chyle is opake in some, as the mammalia, and transparent like the lymph in others, as in birds, fishes, and reptiles.

In the organs of circulation several very important distinctions take place.

Some appear to have no circulating system, as insects and zoophytes. In those which possess circulating organs, some have a double circulation, or in them all the venous blood passes through the lungs, before it again enter the arterial system, as man, mammalia, birds, fishes, and many of the mollusca; others have only a single circulation, or in these a great part of the venous blood re-enters the arterial system, without passing through the lungs, as in reptiles. The structure and position of the heart is different in various classes. In some it is double, one part serving for circulating the blood through the lungs, and the other for distributing it through the rest of the body; and in this case the parts may be united, as in man, the mammalia, and birds, or they may be distinct, as in the cuttle-fish. In others the heart is single, or consists of one ventricle, which may be situated either at the base of the general artery, as in snails and some other mollusca, or at the base of the pulmonary artery, as in fishes.

The organs of respiration display striking varieties, first, according to the element which is to serve as the medium; if this be air, it is received into the interior of the respiratory organs; if it be water, it merely glides over the surface of lamellae, which have been named branchiae, as in fishes and many of the mollusca, or of fringes, as in some worms. The air may be admitted into the body by one opening or by many. The former is the case with all animals who have proper lungs; the tube which receives the air is subdivided into numerous branches terminating in cells, which are reunited, usually, into two masses, which the animal can at pleasure compress or dilate. In insects, which respire through many openings, the air vessels are most minutely ramified, so as to admit the air to every part of the body, and these animals are said to respire by tracheæ. Lastly, The zoophytes, with the exception of the echinodermata, appear to have no respiratory organs.

There are only two general differences in the organs of voice, and these respect the position of the glottis, where the sound is formed. In birds, this is situated at the base of the windpipe, where this divides into two branches going to the lungs; in quadrupeds and General reptiles, it is placed at the commencement of the windpipe, at the root of the tongue. Only these three classes have a glottis; in others sounds are produced by various mechanical means, by which the external air, or that contained within some part of their bodies, is set in rapid motion.

The differences which take place in the organs of generation are of two kinds, as they relate to the action itself, and to the consequences of this action. In a few animals which mostly belong to the zoophytes, there is no copulation, but the young grows upon the body of the parent, like a shoot upon a tree: others propagate only by copulation, and are of course of two sexes; these, however, may be distinct in different animals, or united in the same; this last only takes place in the mollusca and the zoophytes: all the vertebral animals and insects have the sexes distinct.

In hermaphrodite animals each individual can generate alone, as the bivalve shell fish; others copulate reciprocally, or each individual performs the double office of male and female; this is the case with snails, and such other of the mollusca as crawl on the belly.

As to the produce of generation, there are three modes in which the offspring is brought forth. Some animals, as some of the zoophytes and of articulated worms, produce shoots which remain for some time on the body of the animals, and these are gemmiparous. Others, as man and the mammalia, contain the fetus within a uterus, to which it is connected by a net-work of blood vessels, and from which it is sent forth alive; these, therefore, are viviparous. A third class, comprehending all the other animals, have the young contained within a shell, and enveloped by a substance which it absorbs before it is hatched; the viper may seem an exception to this division, as it brings forth its young alive; but then these have been hatched in the receptacle which contained the eggs; these animals are called oviparous.

Lastly, The organs of secretion show some diversity. All the vertebral animals and some mollusca secrete by means of glands situated in various parts of the body, or at least by means of expansions of vessels. The only secretory organs in insects seem to be tubes of various lengths, which attract, with the spongy tissue of their sides, those fluids which they are to separate from the general nutritious mass. The secretory organs in the zoophytes are very imperfectly understood.

These are the principal general differences which we had to notice as taking place in animals. The following Table exhibits a comprehensive view of these, arranged in the order in which we have enumerated them.

1. OSSIFICATION. A. a. Animals with an internal bony skeleton. MAN, MAMMALIA, BIRDS, REPTILES, FISHES properly so called. b. ——— with an internal cartilaginous skeleton. CARTILAGINOUS FISHES. R. a. ——— with an external horny skeleton. PERFECT INSECTS, LITHOPHYTES. b. Animals b. Animals with an external cretaceous skeleton.

Crustacea, and most of the Zoophytes.

C. —— without a skeleton.

Larvae of Insects, Worms, Polyphi.

2. IRRITABILITY.

A. Animals which have the whole body muscular.

Most larvae of Insects, Worms, Polyphi.

B. —— which have the muscles covering the skeleton.

Man, Mammalia, Birds, Fishes, Reptiles.

C. —— which have the muscles covered by the skeleton.

Perfect Insects, Crustacea.

3. SENSATION.

A. Animals which have a brain and nerves readily distinguished from the spinal marrow.

Man, Mammalia, Birds, Fishes, Reptiles.

B. —— which have a brain and nerves scarcely to be distinguished from the spinal marrow.

Insects, Crustacea, Worms.

C. —— which have no apparent sensorium.

Zoophytes.

4. DIGESTION.

A. Animals which have one stomach, or more, readily distinguished from the oesophagus and the alimentary canal.

Man, Mammalia, Birds, Crustacea.

B. —— which have the stomach distinguished from the oesophagus and alimentary canal only by certain swellings.

Fishes and Reptiles.

C. —— which have only an alimentary canal.

Insects, Worms, Zoophytes.

5. CIRCULATION.

A. a. Animals with red blood, and a heart having two ventricles and two auricles.

Man, Mammalia, Birds.

b. —— with a heart having one ventricle divided into several cavities, and two auricles.

Reptiles.

c. —— with a heart having but one ventricle and one auricle.

Fishes.

B. Animals with white blood, and a heart formed of a longitudinal canal jointed and relations, contractile.

Most Crustacea, Worms.

C. —— without a heart, but with fluids contained in vessels.

Insects, Zoophytes.

6. RESPIRATION.

A. a. Animals which respire by means of lungs not adhering and spongy.

Man, Mammalia.

b. —— which respire by means of lungs not adhering, but formed of cells, and muscular.

Reptiles.

c. —— which respire by means of lungs adhering to the ribs, and furnished with appendages.

Birds.

B. —— which respire by means of gills of various forms.

Fishes, Crustacea.

C. —— which respire by means of stigmata, or holes situated in different rings.

Insects, Terrestrial Worms.

D. —— which respire by means of tracheæ, or by external fringed bodies.

Aquatic Worms.

E. —— which appear to have neither stigmata nor tracheæ.

Zoophytes ex. Echinodermata.

7. GENERATION.

A. Animals viviparous.

Man, Mammalia.

B. —— oviparous.

Birds, Fishes, Reptiles, Insects, Crustacea, Worms.

C. —— which may be propagated by cuttings.

Worms, Polyphi.

8. SECRETION.

A. Animals secreting by means of glands.

Man, Mammalia, Birds, Fishes, Reptiles, and some Mollusca.

B. —— which appear to have no glands.

Some Mollusca, Insects, Worms, Zoophytes.

CHAP. II. GENERAL RELATIONS WHICH TAKE PLACE AMONG THE VARIATIONS OF ORGANIZATION AND FUNCTIONS.

We shall best observe these relations by comparing together the several functions, two by two.

To begin with one of the most obvious, respiration, we perceive that this is always regulated by the motion of the nutritious fluid. In animals which are furnished with a heart and vessels, there is a central receptacle, in which this fluid is collected, and from which it is distributed to every part of the body; the heart is its great goal, from which it sets out, and to which it must return before performing a new circuit.

It must, therefore, at its source undergo the action of the air, and accordingly, before it is sent through the general artery, to the various organs, it is circulated through the lungs or branchiae for this purpose. But in animals, as insects, which have neither heart nor vessels, this correspondence is unnecessary. In them the nutritious fluid has no regular motion, no general source; it could not have been prepared in a separate organ, before its distribution to the rest of the body, as, exuding through the pores of the intestinal canal, it continually bathes the several parts, and introduces fresh particles between those which compose them. The air, therefore, could exert its action only at the very points of this introduction, and the very instant when it happens. This is extremely well provided for by the disposition of the trachea, as there is no one solid point in the bodies of insects to which the fine ramifications of the air-vessels do not extend, and at which the chemical action of the air does not take place. As we clearly see the causes of these relations between the organs belonging to these two functions of respiration and circulation, we are authorized to conclude that other relations, which are found to hold between them, depend upon causes of the same kind, though perhaps not equally evident.

For instance, of those animals who have blood-vessels and a double circulation, some respire by admitting the air immediately into the spongy substance of the lungs, and in these the two trunks of the large arteries approach each other, and are furnished with muscular ventricles united into one fleshy mass; others respire through the medium of water passing between the folds of their branchiae, and in these the two trunks are always separated, whether each be furnished with a separate ventricle as in the cuttle-fish, or both have a common ventricle as in fishes and the mollusca.

The relation which subsists between respiration and motion is more easily explained. We find, that those animals which move quickest, and are constantly resident in the air, stand most in need of pure air, and can obtain it with the greatest facility. The constant demand for fresh air, is found by modern chemistry to be owing to the loss of irritability in the muscular fibre, which is supplied by something from the air. Birds, therefore, who, from the swiftness of their motion, and consequent loss of irritability, have the greatest demand for fresh air, have also the most complete and extensive respiratory organs. In reptiles, again, whose motion is generally very slow, and whose irritability is retained with great obstinacy, these organs are incomplete, and their vessels confounded with those of the general circulation, and they can exist long without air. The mammalia seem to hold the middle rank between these two extremes.

The relations which take place between the differen- ces of the organs of sensation, with those of respiration, likewise deserve attention.

In animals with cold blood, the external senses are much less acute than in the warm-blooded animals; and in the former the brain is less, and does not completely fill the skull. This is doubtless owing to the slower motion of the cold-blooded animals requiring less nervous energy.

The digestive organs are found to possess more power in proportion as those of respiration are more active, as the great waste occasioned by these must be compensated by a proportional supply of aliment received. Hence in birds, the stomach is extremely powerful, the digestion very vigorous, and the demand for food frequent and importunate; while reptiles require very little nourishment, and can remain very long without a fresh supply.

We have seen the relations which subsist between the organs of respiration and those of digestion. These last are also immediately related to the organs of motion and of sensation; for the nature of the aliment by which the animal is to be nourished is completely determined by the disposition of the alimentary canal; but if the animal had not its organs of sensation and of motion calculated for distinguishing and procuring its proper food, it is evident that it could not exist: thus an animal who can digest only flesh, must of necessity be enabled to perceive, to pursue, to seize, to overcome, and tear in pieces its proper prey. It must therefore possess a piercing sight, an acute smell, a rapid motion, agility, and considerable strength in its jaws and talons. Accordingly, we never see existing in the same animal a tooth formed for cutting flesh together with a horny foot; this explains why every animal with hoofs is herbivorous, and why hoofs indicate grinding teeth with flattened crowns, a very long alimentary canal, a large stomach, or several stomachs, and many other similar relations. Among all these relations there are many which have something in common, and there are always some in which the differences are few, so that by bringing together those which have the nearest resemblance, we are enabled to form a kind of series, which will appear gradually to proceed from a primitive standard. Hence the idea of a scale of beings, which some naturalists have formed, exhibiting a regular gradation, beginning at the most perfect, and descending to the most simple state of organization, or vice versa. As the links which constitute this chain are by no means entirely known, a perfect scale of beings is at present not to be expected.

The following table displays a series of animals, beginning with the most simple state of organization, and ascending to the most perfect. SCALE of Animals according to the greater or less simplicity of their Structure.

1. Having only a stomach, - Polypes. Hydra. Linné. - Biphoros. Forskall. - Vinegar cels. - Fibrio.

2. A stomach and intestines, - Sea anemonies. Linné. - Actinias. - Nettles. - Medusae. - Argonauts. - Beröe. - Most animalcula of vegetable infusions.

3. Having beside these an external organ for respiration in the water, - Flower-polypes. Miller. - Vorticelle. - Brachioni. - Botrylli. Pallas.

4. Having besides these, some viscera, a system of absorbents, organs of generation, (but not of copulation) and a net-work of nerves, - Thetis. Linné. - Anomiae. - Nereis. - Animals of the bivalve shells.

5. Having beside, a blood-vessel, and sometimes the sense of seeing, - Intestinal worms.

6. Having beside, organs of copulation (hermaphrodites) a heart without auricles, but with distinct pulsations, nervous ganglia, the sense of vision, and an imperfect organ of mastication, - Leeches. - Snails. - Animals of the univalve shells.

7. Having besides a brain, organs of locomotion, male and female organs of generation distinct, sometimes the sense of hearing, and an external bony system, - Insects.

8. Having rudiments of an internal bony system, a heart and blood-vessels, - Cartilaginous fishes.

9. Having a complete internal bony system, - Fishes properly so called.

10. Having internal lungs, and an organ of smelling, - Amphibia.

11. Having besides a bilocular heart, - Birds.

12. Having perfect organs of taste and mastication, organs for secreting milk, and a uterus, - Mammalia. - Man.

CHAP. III. ARRANGEMENT OF ANIMALS FOUNDED ON THE GENERAL DIFFERENCE OF THEIR ORGANIZATION.

HAVING taken a survey of the general differences which take place in the organization and functions of animals, and of the relations which subsist among these differences; we are now to proceed to a summary view of the whole animal kingdom, and consider what is common in the organization of the various classes of which it is composed.

The whole animal kingdom is generally divided into two great families, that of the vertebral animals, who have red blood; and that of the invertebral animals, almost all of which have white blood.

In the first division we always find an interior articulated skeleton, of which the principal support is the vertebral column, having the head at its atlantal extremity, and containing within its cavity the general origin of the nerves; its sacral extremity is commonly prolonged to form a tail. The ribs, which are seldom wanting, are situated on both sides of this column (c).

(c) As the terms generally employed in the human anatomy are by no means calculated for describing the structure These animals have never more than four limbs; but in some of them two of these are wanting, in others all.

Their brain is always contained within a peculiar cavity of the head called the cranium; all the spinal nerves send off filaments to assist in forming a nervous chord, which is derived from one of the nerves of the cranium, and is distributed to most of the viscera.

They have always five senses: two eyes which they can move at pleasure; the ear has always at least three semicircular canals; the organ of smell is always confined to cavities in the fore part of the head; there is always at least one fleshy ventricle, by which the circulation of the blood is carried on; sometimes there are two ventricles, which are always united.

The lymphatic vessels are always distinct from the blood-vessels.

The jaws are always situated horizontally, and separate from above downwards.

The alimentary canal is continued from the mouth to the anus, which is always situated behind the bones with which the sacral extremities are articulated.

The intestines are enveloped in a membranous bag, called peritoneum.

There are always a liver, and a pancreas or sweet-bread, by which liquors are secreted for the purposes of digestion, and a spleen, in which one part of the blood, which goes afterwards to the liver, undergoes some previous change.

The urine is always separated by two kidneys, which are situated on both sides of the vertebral column without the peritoneum, and above which are always two bodies called atrabiliary capsules, the use of which is unknown. The vertebral animals are subdivided into two sections; the hot-blooded, and the cold-blooded.

In the hot-blooded vertebral animals there is always a heart and a double circulation. Respiration is carried on by means of lungs, and without the exercise of this function they cannot exist.

The brain in these animals completely fills the cavity of the skull, and their eyes close by means of lids. The tympanum of their ear is sunk in the solid bone of the skull, as the parts of the labyrinth are entirely surrounded by bone; besides the semicircular canal, there is always an organ with two spiral cavities, like the shell of a snail; the nostrils serve for the passage of the air in breathing, and form a communication with the mouth. The trunk is always surrounded by the ribs, and there are for the most part four limbs.

The cold-blooded vertebral animals are deficient in several of these particulars; many of them want ribs, and some of them have no limbs. In them the brain never entirely fills the cavity of the skull, and their eyelids are seldom moveable; the tympanum of their ear, as also the small bones, is often wanting; the spiral cavity always; when the tympanum is present, it is never sunk within the skull.

Each of these two divisions is again subdivided into two classes; the former into the mammalia and the birds; the latter into the fishes and the reptiles: the structure of these classes will be considered in their proper place.

The invertebrated animals have fewer common circumstances, and constitute a less regular series than those of which we have been speaking; their hard parts, when they are present, are generally, at least when articulated, placed externally. No part of their nervous system is contained within a bony sheath, but floats in a common cavity with the viscera.

The brain only is placed above the alimentary canal; from it proceed two branches which embrace the gullet like a collar, and from which the general bundle of the nerves is formed. In these animals respiration is never carried on by means of cellular lungs, and they are all destitute of voice; their jaws have no particular direction, and their mouths are often merely suckers; they have no kidneys, and consequently secrete no urine; if they have limbs, these are always at least six in number.

Considered in an anatomical point of view, they may be divided into five classes, namely, the mollusca, the crustacea, insects, worms, and zoophytes. We shall treat of these several classes in the order in which we have enumerated them.

CHAP. IV. MAMMALIA, OR QUADRUPEDS.

Sect. I. General Observations.

A question has been started by some fanciful philosophers, "Whether man is naturally a biped or a quadruped?" and much ingenuity has been employed to establish the latter opinion. But it is presumed that few of their readers have been made converts to such an opinion, and that not many of ours will require much argument to persuade them of their erect destination. It may therefore suffice to observe, that this erect position is best adapted to the conformation of the human head, and the ponderous quantity of human brains:—that the articulation of the os occipitis with the first vertebra of the neck, is differently constructed from that of quadrupeds, with the obvious design that man should be able to move his head in every direction with the greatest facility:—that the human species (and also monkeys) are destitute of that strong ligament or tendinous aponeurosis, vulgarly called paravex, which quadrupeds possess (as a kind of stay-tape), to prevent the head from sinking to the earth; to which, from its natural position, it must be very prone:—and that our eyes and ears are, fortunately, not

structure of the inferior animals, we shall in this article make use of others, with which we have been favoured by Dr Barclay, the ingenious lecturer on anatomy, to whose publication on anatomical nomenclature we refer the reader for their explanation. not placed as those of the quadrupeds. The axis of the human eye is nearly perpendicular with a vertical section of the head; whereas, in the brute creation (the larger ape excepted), the position of the eyes forms an acute angle:—nature has also furnished other animals with a suspensorium oculi, a muscle which the erect attitude renders needless, though highly necessary in the prone; consequently, whoever tries the experiment will find that, in the inclined direction, both his eyes and his ears are in the most unfavourable situation possible for quick hearing or extensive vision. In fine, the shape, breadth, strength of the vertebrae of the back and loins, are all coincident with the erect attitude of the trunk.

All quadrupeds have a covering of hair, wool, &c., to defend them from the injuries of the weather, which varies in thickness according to the season of the year and difference of the climate; thus in Russia and the northern countries, the furs are very thick and warm, while the little Spanish lap-dogs, and Barbary cows, have little or no hair at all.

The cutis and cuticula in quadrupeds are disposed much in the same way as the human, only more elastic; immediately under this, there is a very thin cutaneous muscular substance called panniculus carnosus, which is common to all quadrupeds, the porcine kind excepted; this principally covers the trunk, serving to shrivel the skin, in order to drive off insects, their tails and heads not being sufficient for this purpose, while their extremities are employed in their support and progression.

It has probably been from observing some muscles of the human body, such as the platysma myoides, crests of the panicle master, and frontales, and the collapsed tunica cellulosa of emaciated subjects, to resemble this thin muscle, that some of the oldest anatomists reckoned such a panniculus among the common teguments of the human body. This Carolus Stephanus has well observed.

Most part of quadrupeds want clavicles, whereby why most their atlantal extremities fall upon their chest, so as quadrupeds to make their thorax proportionally narrower than the human. This small distance of their atlantal extremities is very necessary for their uniform progression: apes indeed and squirrels have clavicles to allow them a more full use of their extremities in climbing; but when they walk on all-fours, they move but indifferently.

Their head is connected to the first vertebra of the neck by two eminences as in man. The vertebrae of the neck are never less than six, or more than nine. The number of the dorsal and other vertebrae differs considerably in the various individuals. The following table exhibits these differences in each species. The brain of these animals is more complicated than that of the other classes.

### TABLE of the Proportional Number of Spinal Vertebrae in various species of Mammalia.

| Species | Dorsal Vertebrae | Lumbar Vertebrae | Sacral Vertebrae | Coccygian Vertebrae | |--------------------------|------------------|------------------|------------------|--------------------| | Man | | | | | | Simia satyrus, Lin. | | | | | | Orang-outang | | | | | | troglodytes | | | | | | Jocko | | | | | | lar. Gibbon | | | | | | paniscus | | | | | | Conita | | | | | | capucina | | | | | | Weeping monkey, sat. | | | | | | rosalia | | | | | | Silky money, marakina | | | | | | patas | | | | | | Patas | | | | | | Maimon, rib-nosed ape | | | | | | cynomolgus | | | | | | Macaca | | | | | | chinensis | | | | | | Chinese monkey | | | | | | sphinx | | | | | | Baboon, papion | | | | | | tinus | | | | | | Magot | | | | | | maimon | | | | | | Mandrill | | | | | | pongo | | | | | | Pongo | | | | | | beelzebul | | | | | | Alosti, howling baboon | | | | | | Lemur catta | | | | | | Macaco | | | | | | gracilis | | | | | | Lori | | | | | | tarsius | | | | | | Tarsier | | | | | | Vespertilio vampyrus | | | | | | Rousette, vampyre bat | | | | | | murinus | | | | | | Common bat | | | | | | noctula | | | | | | Noctule, great bat | | | | | | ferrum equinum | | | | |

TABLE | Species | Dorsal Vertebra | Lumbar Vertebra | Sacral Vertebra | Coccygian Vertebra | |-------------------------------|-----------------|-----------------|-----------------|--------------------| | Lemur volans. Flying lemur | 12 | 6 | 1 | 22 | | Erinaceus europaeus. Hedgehog | 15 | 7 | 4 | 12 | | — caudatus. Tarec | 15 | 6 | 3 | 8 | | Sorex, mus araneus. Musetta, shrew | 12 | 7 | 3 | 17 | | Talpa europaea. Mole | 13 | 6 | 7 | 11 | | Ursus maritimus. White bear | 13 | 6 | 7 | 11 | | — arctos. Brown bear | 14 | 6 | 5 | 4+ | | — meles. Badger | 15 | 5 | 3 | 16 | | — gulo. Glutton | 16 | 5 | 3 | 18 | | Viverra. Coati | 14 | 6 | 1 | 10+ | | Ur. lotor. Raccoon | 14 | 7 | 3 | 20 | | Mustela lutra. Otter | 14 | 6 | 3 | 21 | | — martes. Marten | 14 | 6 | 3 | 18 | | — vulgaris. Weasel | 14 | 6 | 3 | 14 | | Viverra civetta. Civet | 13 | 6 | 3 | 20 | | Felis leo. Lion | 13 | 6 | 3 | 23 | | — tigris. Tiger | 13 | 7 | 4 | 19 | | — pardus. Panther | 13 | 7 | 3 | 24 | | — concolor. Cougar | 13 | 7 | 3 | 22 | | — catus. Cat | 13 | 7 | 3 | 22 | | Canis familiaris. Wolf-dog | 13 | 6 | 3 | 22 | | — lupus. Wolf | 13 | 7 | 3 | 19 | | — vulpes. Fox | 13 | 7 | 3 | 20 | | — hyaena. Hyena | 16 | 4 | 2 | 8+ | | Didelphis cancrifaga. Cayenne opossum, crab-eater | 13 | 6 | 5 | 16+ | | — murina. Marmose | 13 | 6 | 1 | 29 | | — orientalis. Phalanger | 13 | 6 | 1 | 30 | | Histrix cristata. Porcupine | 14 | 5 | 4 | 8+ | | Lepus timidus. Hare | 12 | 7 | 4 | 20 | | — cuniculus. Rabbit | 12 | 7 | 2 | 20 | | Cavia capybara. Cabe | 13 | 6 | 2 | 4+ | | — cobaya. Guinea pig | 13 | 6 | 4 | 6 | | — pacu. Paca, or spotted cavy | 13 | 6 | 5 | 7 | | — aguti. Agouti | 12 | 8 | 4 | 7 | | Castor fiber. Beaver | 15 | 5 | 3 | 23 | | Sciurus volans. Flying squirrel | 12 | 8 | 3 | 13 | | Mus marmotta. Marmotte | 13 | 7 | 6 | 22 | | — arvalis. Field mouse | 13 | 7 | 3 | 15 | | — amphibius. Water rat | 13 | 7 | 4 | 23 | | — rattus. Black rat | 13 | 9 | 3 | 26 | | — decumanus. Norway rat | 13 | 7 | 4 | 23 | | — musculus. Common mouse | 12 | 7 | 4 | 24 | | — sylvestris. Field or harvest rat | 12 | 7 | 3 | 23 | | — cricetus. Hamster | 13 | 6 | 4 | 15 | | — glis. Fat dormouse | 13 | 7 | 2 | 18 | | — querceinus. Garden dormouse | 13 | 7 | 4 | 24 | | Myrmecophaga didactyla. Ant-eater | 16 | 2 | 4 | 40 | | Manis pentadactyla. Pangolin | 15 | 5 | 3 | 28 | | — tetradactyla. Long-tailed manis | 13 | 5 | 2 | 45 | | Dasypus. Armadillo | 11 | 4 | 3 | 30 | | Bradypus didactylus. Two toed sloth | 23 | 2 | 4 | 7+ | | Elephas indicus. Elephant | 20 | 3 | 4 | 14 | | Sus scrofa. Hog | 14 | 5 | 3 | 4 |

TABLE, ### TABLE, &c. continued.

| Species | Dorsal Vertebra | Lumbar Vertebra | Sacral Vertebra | Coccygian Vertebra | |--------------------------|-----------------|-----------------|-----------------|-------------------| | Tapirus. Tapir | 20 | 4 | 3 | 12 | | Rhinoceros | 19 | 3 | 4 | 22 | | Camelus bactrianus. Camel.| 12 | 7 | 4 | 17 | | dromedarius. Dromedary | 12 | 7 | 4 | 18 | | Cervus elaphus. Stag | 13 | 6 | 3 | 11 | | Camelopardalis. Camelopard.| 14 | 5 | 4 | 18 | | Antelope cervicapra. Antelope | 13 | 6 | 5 | 15 | | dorcas. Gazelle | 13 | 5 | 5 | 11 | | rupicapra. Chamois goat | 13 | 5 | 4 | 7+ | | Capra hircus. Goat | 13 | 6 | 4 | 12 | | Ovis aries. Sheep | 13 | 6 | 4 | 16 | | Bos taurus. Ox | 13 | 6 | 4 | 16 | | Equus caballus. Horse | 18 | 6 | 2 | 17 | | quagga. Cougar | 18 | 6 | 7 | 18 | | Phoca vitulina. Seal | 15 | 5 | 2 | 12 | | Delphinus delphis. Dolphin | 13 | 7 in all | - | - | | phocena. Porpoise | 13 | 66 | - | - |

Their eyes have only two lids, and they agree with man in having the internal ear furnished with four little bones articulated with each other, and a completely spiral cochlea, and a tongue entirely soft and fleshy. Their heart, lungs, and diaphragm resemble those of man in their general structure; and differ only in a few circumstances, which will be best seen in the exemplification of their structure, which is presently to be given.

In treating of quadrupeds we shall divide them into the carnivorous, or rather those which feed indiscriminately on flesh and vegetables, and the granivorous. The structure of the former we shall exemplify in the dog, that of the latter in the cow.

**Sect. II. The Anatomy of a Dog.**

We may first observe of this animal, as of most quadrupeds, that its legs are much shorter in proportion to its trunk than in man, the length of whose steps depends entirely on the length of his sacral extremities; however, to balance this, the trunk of the animal is proportionally longer and smaller, his spine more flexible, by which he is able at each step to bring his sacral nearer to his atlantal extremities. His common teguments are much a-kin to those of other quadrupeds, only they allow little or no passage for sweat; but when he is over-heated, the superfluous matter finds an exist by the salivary glands, for he lolls out his tongue and slavers plentifully. We are not, however, to suppose, that because a dog does not sweat, he has no insensible perspiration. That a dog perspires is evident, because one of these animals can trace another by the scent of his footsteps; which could not happen if a large quantity of perspirable matter was not constantly going off.

The pyramidal muscles are wanting, to supply which the rectus is inserted fleshy into the os pubis.

The brain is proportionally much smaller than the brain human; but as in man, it is divided into cerebrum and cerebellum, and these two parts bear nearly the same proportion to one another as in us. There was no such occasion for so great a quantity of brain in these animals as in man; seeing that in them all its energy is employed in their progression, while man has a great waste of spirits in the exercise of his reason and intellectual faculties. And besides all this, a bulky brain would be inconvenient to these creatures, in so far as it would add considerably to the weight of the head; which having the advantage of a long lever to act with, would require a much greater force to support it than it does now; for the heads of the greatest part of quadrupeds are not near so heavy as they would at first sight seem to be, from the frontal sinuses being produced a great way upwards to enlarge the organ of smelling.

The pits in the anterior part of their skull are much more conspicuous than in the human; which may be occasioned by the depending posture of these creatures heads while they gather their food: The brain at this time gravitating much on the bones while they are as yet soft, will gradually make impressions upon them at those places where it rises into eminences. This is prevented in man mostly by his erect posture.

The falx is not near so large in quadrupeds as in man, Falx, as they have little occasion to lie on either side, and the two hemispheres of the brain are in a great measure hindered from justling against one another in violent motions, by the brain's insinuating itself into the above-mentioned pits.

The second process of the dura mater, or tentorium cerebello super-expansum, is considerably thicker and stronger. stronger than in man. This membrane is generally os- sified, or we find the place of it supplied by a bone, that it may the more effectually keep off the superincumbent brain from the cerebellum in rapid motions, which other- wise would be of bad consequence.

The olfactory nerves are very large, and justly de- serve the name of processus mamillaris. They are hol- low, and consist of a medullary and cineritious sub- stance, and at first sight appear to be the frontal ven- tricles of the brain produced; but in man they are small, and without any discernible cavity. The reason of this is pretty evident, if we consider how this animal's head is situated; for the lymph continually gravitating upon the inferior part of the ventricles, may thus elon- gate and produce them; but from this very inferior part the olfactory nerves rise, and are sent immediately through the ethmoid bone into the nose. Hence the ancients, thinking they were continued hollow into the nose, believed they were the emunctories of the brain: in the brain of sheep, which by its firm texture is the best subject of any for searching into the structure of this part, we evidently see, that the name of the sigmoid cavity was very properly applied by the ancients to the lateral ventricles of the brain; which are really of a greater extent than they are ordinarily painted by ana- tomists, reaching farther backwards, and forwards again under the substance of the brain. The cortical and me- dullary parts, as well as the corpus callosum, are similar to those parts in man.

The nates and testes deserve this name much better here than in the human body, with respect to each other. They are larger in the quadrupeds; and hence we perceive that there is no great reason for ascribing the different operations to any particular size or shape of these parts. They are here also of different colours; the nates being of the colour of the cortical, and the testes of the medullary substance of the brain; whereas in man they are both of one colour. The reason of these differences, and others of the like nature to be met with, we shall not pretend to determine; for we have hitherto such an imperfect knowledge of the brain itself, that we are entirely ignorant of the va- rious uses of its different parts. We may in general conclude, that the varying in one animal from what it is in another, is fitted to the creature's particular way of living.

The rete mirabile Galeni, situated on each side of the sella turcica, about which there has been so much dis- pute, is very remarkable in these animals. This net- work of vessels is nothing else than a continuation of the internal carotid arteries, which entering the skull, divide into a vast number of minute branches running along the side of the sella turcica; and, uniting after- wards, are spent on the brain in the common way. Ga- len seems with justice to suppose, that this plexus of ves- sels serves for checking the impetuosity of the blood destined for the brain.

The tongue, in consequence of the length of the jaws, is much longer than ours; and as this creature feeds with his head in a depending posture, the bolus would always be in danger of falling out of the mouth, were it not for several prominences or papillae placed mostly at the root of the tongue, and crooked back- wards in such a manner as to allow any thing to pass easily down to the jaws, but to hinder its return. By the papillae also the surface of the tongue is increased, and a stronger impression is made on the sensation of taste. In some animals who feed on living creatures, these tenter-hooks are still more conspicuous; as in sev- eral large fishes, where they are almost as large as their teeth in the fore part of their mouth, and near as firm and strong.

The nose is generally longer than in man, and its ex- ternal passage much narrower. The internal structure is also better adapted for an acute smelling, having a larger convoluted surface on which the membrana schnei- deriana is spread; and this is to be observed in most quadrupeds, who have the ossa spongiosa commonly large, and these too divided into a great number of excessively fine thin lamellae. The sensibility seems to be increased in proportion to the surface; and this will also be found to take place in all the other senses. The elephant, which has a head pretty large in proportion to its body, has the greatest part of it taken up with the cavity of the nose and frontal sinuses; which last extend almost over their whole head, and leave but a small cavity for their brains. A very nice sense of smelling was not so absolutely necessary for man, who has judgment and experience to direct him in the choice of his food; whereas brutes, who have only their senses, must of necessity have these acute, some having one sense in greater perfection than others, according to their different way of life. We not only conclude a priori from the large expanded membrana schneideriana, that their sense of smelling is very acute, but we find it so by cows and horses distinguishing so readily betwixt noxious and wholesome herbs, which they do principal- ly by this sense.

The external ear in different quadrupeds is differ- ently framed, but always calculated for the creature's manner of life. In shape it commonly resembles the oblique section of a cone from near the apex to the basis. Hares, and such other animals as are daily ex- posed to insults from beasts of prey, have large ears di- rected backwards, their eyes warning them of any dan- ger before; rapacious animals, on the other hand, have their ears placed directly forwards, as we see in the lion, cat, &c. The slow hounds, and other animals that are designed to hear most distinctly the sounds coming from below, have their ears hanging down- wards; or their ears are flexible, because they move their head for the most part with greater difficulty than man. Man, again, who must equally hear sounds com- ing from all quarters, but especially such as are sent from about his own height, has his external ear placed in a vertical manner, somewhat turned forward. In short, wherever we see a specialty in the make of this organ in any creature, we shall, with very little reflec- tion, discover this form to be more convenient for that creature than another. The animal also has the power of directing the cone of the ear to the sonorous body without moving the head. There are some differences to be observed in the structure of the internal ear in different animals; but we know so very little of the use of the particular parts of that organ in the human sub- ject, that it is altogether impossible to assign reasons for these variations in other creatures.

All quadrupeds have at the internal canthus of the eye a strong firm membrane with a cartilaginous edge, which may be made to cover some part of their eye; and this is greater or less in different animals as their eyes are more or less exposed to danger, in searching after their food. This membrana nictitans, as it is called, is not very large in this animal. Cows and horses have it so large as to cover one half of the eye like a curtain, and at the same time it is sufficiently transparent to allow abundance of the rays of light to pass through it. Fishes have a cuticle always over their eyes, as they are ever in danger in that inconstant element. In this then we may also observe a sort of gradation.

All quadrupeds have a seventh muscle belonging to the eye, called suspensorius. It surrounds almost the whole optic nerve, and is fixed into the sclerotic coat as the others are. Its use is, to sustain the weight of the globe of the eye, and prevent the optic nerve from being too much stretched, without obliging the four straight muscles to be in a continual contraction, which would be inconvenient; at the same time this muscle may be brought to assist any of the other four, by causing one particular portion of it to act at a time.

The next thing to be remarked is the figure of the pupil, which is different in different animals, but always exactly accommodated to the creature's way of life, as well as to the different species of objects that are viewed. Man has it circular, for obvious reasons: an ox has its oval, with the longest diameter placed transversely, to take in a larger view of his food; cats, again, have theirs likewise oval, but the longest diameter placed perpendicularly; they can either exclude a bright light altogether, or admit only as much as is necessary. The pupil of different animals varies in wideness, according as the internal organs of vision are more or less acute: Thus cats and owls, who seek their prey in the night, or in dark places (and consequently must have their eyes so formed as that a few rays of light may make a lively impression on the retina), have their pupils in the day-time contracted into a very narrow space, as a great number of rays would oppress their nice organs; while in the night, or where the light is faint, they open the pupil, and very fully admit the rays. In the same way, when the retina is inflamed, a great number of rays of light would occasion a painful sensation; therefore the pupil is contracted: on the contrary, in dying people, or in a beginning amaurosis, it is generally dilated, as the eyes on such occasions are very difficultly affected, and as it were insensible.

The posterior part of the choroid coat, which is called tapetum, is of different colours in different creatures. For oxen, feeding mostly on grass, have this membrane of a green colour, that it may reflect upon the retina all the rays of light which come from objects of that colour, while other rays are absorbed: Thus the animal sees its food better than it does other objects. Cats and owls have their tapetum of a whitish colour; and for the same reasons have the pupil very dilatable, and their organs of vision acute: And we shall find, that all animals see more or less distinctly in the dark, according as their tapetum approaches nearer to a white or black colour. Thus dogs, who have it of a grayish colour, distinguish objects better in the night than man, whose tapetum is dark brown; and who, it is believed, sees worst in the dark of any creature: it being originally designed that he should rest from all kinds of employment in the night-time. The difference then of the colour of the tapetum, as indeed the fabric of any other part in different creatures, always depends on some particular advantage accruing to the animal in its peculiar manner of life from this singularity.

We look on it as a general rule, that all quadrupeds, Neck as having occasion to gather their food from the ground, are provided with longer necks than man; but as a long neck not only gives the advantage of too long a lever to the weight of the head, but also, when the animal is gathering his food, makes the brain in danger of being oppressed with too great a quantity of blood, by the liquor in the arteries having the advantage of a descent, while that in the veins must mount a considerable way contrary to its own gravity; it was therefore necessary that a part of the length of the neck should be supplied by the length of the jaws. Thus we see horses, cows, &c. who have no occasion for opening their mouths very wide, yet have long jaws. Bulldogs, indeed, and such animals as have occasion for very strong jaws, must of necessity have them short; because the longer they are, the resistance to be overcome acts with a longer lever. Another exception to this general rule, is such animals as are furnished with something analogous to hands to convey their food to their mouths, as cats, apes, &c. The teeth of this creature plainly show it to be of the carnivorous kind; for there are none of them made for grinding its food, but only for tearing and dividing it. It has six remarkably sharp teeth before, and two very long tusks behind; both of which the ruminating animals want. These are evidently calculated for laying very firm hold of substances, and tearing them to pieces; and the vast strength of the muscles inserted into the lower jaw, assists greatly in this action; while the grinders have sharp cutting edges, calculated for cutting flesh, and breaking the hardest bones. Even its posterior teeth are not formed with rough broad surfaces as ours are; but are made considerably sharper, and press over one another when the mouth is shut, that so they may take the firmer hold of whatever comes betwixt them.

When we open the mouth, we see the amygdalæ very prominent in the posterior part of it; so that it would appear at first view, that these were inconveniently placed, as being continually exposed to injuries from the hard substances this creature swallows; but upon a more narrow scrutiny, we find this provided for by two membranous capsules, into which the amygdalæ, when pressed, can escape, and remove themselves from such injuries.

The velum pendulum palati is in this creature considerably longer than in man, to prevent the food from getting into his nose; which would happen more frequently in this animal than in man, because of its situation while feeding.

In this subject, as well as in other quadrupeds, there is no uvula; but then the epiglottis, when pressed down, covers the whole rima entirely, and naturally continues so: there is therefore a ligament, or rather muscle, that comes from the os hyoides and root of the tongue that is inserted into that part of the epiglottis where it is articulated with the cricoid cartilage, which serves to raise it from the rima, though not so strongly but that it may with a small force be clapped down again.

It may be asked, however, Why the uvula is wanting here, and not in man? This seems to be, that quadrupeds, who swallow their food in a horizontal situation, have no occasion for an uvula, though it is necessary in man on account of his erect situation.

In the upper part of the pharynx, behind the cricoid cartilage, there is a pretty large gland to be found, which serves not only for the separation of a mucous liquor to lubricate the bolus as it passes this way, but also supplies the place of a valve, to hinder the food from regurgitating into the mouth, which it would be apt to do by reason of the descending situation of the creature's head. In man, the muscle of the epiglottis is wanting, its place being supplied by the elasticity of the cartilage.

The gullet is formed very much in the same way as the human. Authors indeed generally allege, that quadrupeds have their gullet composed of a double row of spiral figures decussating one another; but this is peculiar to ruminating animals, who have occasion for such a decussation of fibres. The action of these you may easily observe in a cow chewing her cud.

The omentum reaches down to the os pubis, which, considering the posture of the animal, we shall find to be a wise provision, since its use is to separate an oily liquor for lubricating the guts and facilitating their peristaltic motion; so in our erect posture the natural gravity of the oil will determine it downward, but in the horizontal position of these creatures, if all the intestines were not covered, there would be no favourable derivation of the fluid to the guts lying in the sacral part of the abdomen, which is the highest; and besides, had the omentum reached much farther down in us, it would not only have supplied too great a quantity of oil to the lower part of the abdomen, but we should have been in continual danger of hernia; and even at present the omentum frequently passes down with some of the other viscera, and forms part of these tumours. To these, however, the dog is not subject, as his viscera do not press so much on the rings of the abdominal muscles, and besides are prevented from passing through by a pendulous flap of fat mentioned No. 35. The sacral and sternal lamella of the omentum is fixed to the spleen, fundus of the stomach, pylorus, liver, &c., in the same way as the human; but the superior having no colon to pass over, goes directly to the back-bone. This serves to explain the formation of the small omentum in the human body; which is nothing but the large omentum, having lost its fat, passing over the stomach and colon, where it reassumes its fat, so proceeds, and is firmly attached to the liver, spine, &c. The strata of fat are pretty regularly disposed through it, accompanying the distribution of the blood-vessels to guard them from the pressure of the superincumbent viscera.

This animal's stomach, though pretty much resembling the human in its shape, is somewhat differently situated. It lies more longitudinal, as indeed all the other viscera do, to accommodate themselves to the shape of the cavity in which they are contained; that is, its sacral orifice is much farther down with respect to the atlantal than the human: by this means the gross food has an easier passage into the duodenum. Again, the fundus of the human stomach, when distended, stands almost directly sternal, which is occasioned by the little omentum tying it so close down to the back bone, &c., at its two orifices; but it not being fixed in that manner in the dog, the fundus remains always dorsal: this also answers very well the shape of the different cavities, the distance betwixt the cardia and fundus being greater than that betwixt the two sides. It seems to be much larger in proportion to the bulk of the animal than the human, that it might contain a greater quantity of food at once; which was very necessary, since this animal cannot at any time get its sustenance as men do. The turbillion is not so large, nor is there any coaction forming the antrum Williumi, as in the stomach of man. It is considerably thicker and more muscular than ours, for breaking the cohesion of their food, which they swallow without sufficient chewing. Hence it is evident the force of the stomach is not so great as some would have it, nor its contraction so violent: otherwise that of dogs would be undoubtedly wounded by the sharp bones, &c., they always take down; for the contraction here is still greater than in the human stomach, which is much thinner. The rugae of the tunica villosa are neither so large, nor situated transversely, as in the human, but go from one orifice to the other: the reason of which difference is, perhaps, that they might be in less danger of being hurt by the hard substances this creature frequently feeds upon; and for the same reason there is not the like stricture at their pylorus.

The intestines of this animal are proportionally much shorter than ours; for the food which these creatures mostly use, soon dissolves, and then putrefies; on which account there was no occasion for a long tract of intestines, but on the contrary that it should be quickly thrown out of the body. The same is to be observed of all the carnivorous animals. The muscular coat of the intestines is also thicker and stronger than the human, to protrude the contents quickly and accurately.

The valvula conniventes are less numerous, and in a longitudinal direction; and the whole tract of the alimentary canal is covered with a slime, which lubricates the intestines, saves them from the acrimony of the excrementitious part, and facilitates its passage.

The duodenum differs considerably in its situation from the human. For in man it first mounts from the pylorus upwards, backwards, and to the right side; then passes down by the gall bladder; and, marching over the right kidney and superior part of the psoas muscles, makes a curvature upwards; and passes over the back bone and vena cava inferior, to the left hypochondrium, where it gets through the omentum, mesentery, and mesocolon, to commence the jejenum, being firmly tied down all the way, the biliary and pancreatic ducts entering in at its most depending part: Whereas, in the dog, the duodenum is fixed at the pylorus to the concave surface of the liver, and hangs loose and pendulous with the mesentery backwards into the cavity of the abdomen; then turning up again, is fixed to the back bone, where it ends in the jejunum; the bile and pancreatic juice are poured into it at the most depending part. Therefore the same intention seems to have been had in view in the formation of this part in both, viz. the giving the chyle, after the liquors of the liver and pancreas are poured into it, a disadvantageous course, so that it might be the more intimately blended with the humours before its entry into the jejunum, where the lacteals are very numerous: And thus, by reason of their different posture, the same design (though by a very different order of the parts) is brought about in both.

The other small guts are much the same with ours, only shorter. The great guts are also shorter and less capacious than in the human body; and we take it for a general rule, that all animals that live on vegetable food, have not only their small guts considerably longer, but also their great guts more capacious, than such creatures as feed on other animals. Hence man, from this form of his intestines, and that of the teeth, seems to have been originally designed for feeding on vegetables chiefly; and still the most of his food, and all his drink, is of that class.

The reason of this difference seems to be, that as animal food is not only much more easily reduced into chyle, but also more prone to putrefaction, too long a delay of the juices might occasion the worst consequences. So it was necessary that their receptacles should not be too capacious; but, on the contrary, being short and narrow, might conduce to the seasonable discharge of their contents. Whereas vegetable food being more difficulty dissolved and converted into an animal nature, there was a necessity for such creatures as fed on it to be provided with a long intestinal canal, that this food in its passage might be considerably retarded, and have time to change its quality into one more agreeable to our nature. Besides which there is another advantage which accrues to man in particular, from having his great guts very capacious: for as he is a rational being, and mostly employed in the functions of social life, it would have been very inconvenient as well as unbecoming for him to be too frequently employed in such ignoble exercises; so that, having this large reservoir for his feces alvine, he can retain them for a considerable time without any trouble.

The appendix vermiformis justly enough deserves the name of an intestinum cæcum in this subject, though in the human body it does not; and it has probably been from the largeness of this part in this and some other animals, that the oldest anatomists came to reckon that small appendicle in man as one of the great guts. On its internal surface we observe a great number of mucous glands. As all these throw out slime, their principal office would seem to be the procuring a sufficient quantity of that matter for the purposes above mentioned. Still, however, there seems to be some unknown use for this organ in other animals; for the appendicula vermiformis in them is either of great size or of great length. In a rat, it is rather larger than the stomach; in others, as swine, and some of the animals which live on vegetables, it has long convolutions, so that the food must be lodged in it for a long time. Thus, probably, some change takes place in the food, which requires a considerable time to effectuate, and though unknown to us, may answer very useful purposes to the animal.

The colon has no longitudinal ligaments; and consequently this gut is not pursed up into different bags or cells as the human: nor does this intestine make any circular turn round the abdomen; but passes directly across it to the top of the os sacrum, where it gets the name of rectum.

At the extremity of the intestinum rectum, or verge of Rectum, the anus, there are found two bags or pouches, which contain a most abominable fetid mucus of a yellow colour, for which we know no use, unless it serves to lubricate the strained extremity of the rectum, and defend it against the asperity of the feces, or to separate some liquor that might otherwise prove hurtful to their bodies. There is nothing analogous to those sacs in the human subject, unless we reckon the mucilaginous glands that are found most frequent and largest about the lower part of the rectum.

The mesentery is considerably longer than in the human body; that, in his horizontal situation, the intestines may rest securely on the soft cushion of the abdominal muscles. The fat is here disposed in the same way, and for the same reason, as in the omentum. The interspaces betwixt the fat are filled with a fine membrane. Instead of a great number of glandular vago to be found in the human mesentery, we find the glands few in number, and those are closely connected together; or there is only one large gland to be observed in the middle of the mesentery of a dog, which, from its imagined resemblance to the pancreas and the name of his discoverer, is called pancreas Asel-Pancreas lii; but the resemblance, if there is any, depends entirely on the connexion, the structure being entirely different. The reason why this in man is as it were subdivided into many smaller ones, may possibly be, that as the guts of a human body are proportionally much longer than those of this creature, it would have been inconvenient to have gathered all the lactea primigenieris into one place; whereas, by collecting a few of these vessels into a neighbouring gland, the same effect is procured much more easily. Whether the food in this animal needs less preparation in its passage through these glands, is a matter very much unknown to us; though it is certain that some changes really do take place.

The pancreas in man lies across the abdomen, tied Pancreas down by the peritoneum; but the capacity of this creature's abdomen not allowing of that situation, it is disposed more longitudinally, being tied to the duodenum, which it accompanies for some way. Its duct enters the duodenum about an inch and a half below the ductus communis.

The spleen of this animal differs from the human Spleen, very much, both in figure and situation. It is much more oblong and thin, and lies more according to the length of the abdomen, like the pancreas. Though the spleen of this creature is not firmly tied to the diaphragm (which was necessary in our erect posture to hinder it from falling downwards), yet by the animal's prone position, its dorsal parts being rather higher than the sternal, it comes to be always contiguous to this muscle, and is as effectually subjected to an alternate pressure from its action as the human spleen is.

The human Liver has no fissures or divisions, unless Liver. we may reckon that small one betwixt the two pylor, where the large vessels enter: Whereas in a dog, and all other creatures that have a large flexion in their spine, as lions, leopards, cats, &c., the liver and lungs are divided into a great many lobes by deep sections, reaching the large blood-vessels, which in great motions of the back bone may easily slide over one another; and so be in much less danger of being torn or bruised, than if they were formed of one entire piece, as we really see it is in horses, cows, and such creatures as have their back bone stiff and immovable. There is here no ligamentum latum connecting the liver to the diaphragm, which, in our situation, was necessary to keep the viscus in its place: Whereas, in this creature, it naturally gravitates forwards, and by the horizontal position of the animal is in no danger of pressing against the vena cava; the preventing of which is one use generally assigned to this ligament in man. Had the liver of the dog been thus connected to the diaphragm, the respiration must necessarily have suffered; for, as we shall see afterwards, this muscle is here moveable at the centre as well as at the sides: But in man the liver is fixed to the diaphragm, mostly at its tendinous part; that is, where the pericardium is fixed to it on the other side; so that it is in no danger of impeding the respiration, being suspended by the mediastinum and bones of the thorax. In consequence of this viscus being divided into so many lobes, it follows, that the hepatic ducts cannot possibly join into one common trunk till they are quite out of the substance of the liver; because a branch comes out from every lobe of the liver; all of which, by their union, form the hepatic duct: whence we are led to conclude, that the hepatico-cystic ducts, mentioned by former authors, do not exist. The gall-bladder itself is wanting in several animals, such as the deer, the horse, the ass, &c.; but, in place of it, in such animals, the hepatic duct, at its beginning, is widened into a reservoir of considerable size, which may answer the same purpose in them that the gall-bladder does in others.

The mediastinum in this creature is pretty broad. The pericardium is not here contiguous to the diaphragm, but there is an inch of distance betwixt them, in which place the small lobe of the lungs lodges; and by this means the liver, &c. of this animal, though continually pressing upon the diaphragm, yet cannot disturb the heart's motion.

The heart is situated with its point almost directly sternally, according to the creature's posture, and is but very little inclined to the left side. Its point is much sharper, and its shape more conoidal, than the human.

The animal has the vena cava of a considerable length within the thorax, having near the whole length of the heart to run over ere it gets at the sinus Lowerianus dexter. In man, as soon as it pierces the diaphragm, it enters the pericardium, which is firmly attached to it, and immediately gets into the sinus Lowerianus; which sinus, in the human subject, by the oblique situation of the heart is almost contiguous to the diaphragm: and by this we discover, that several authors have taken their delineations of the human heart from brutes; which is easily detected by the shape and situation of the heart, and long vena cava, within the thorax. This was one of the faults of the curious wax work that was shown at London and Paris, which was plainly taken from a cow.

This situation of the heart of the creature agrees best with the shape of its thorax, which is lower than the abdomen.

The egress of the large blood-vessels from the heart is somewhat different from the human: For here the right subclavian comes off first: and as a large trunk runs some way upwards before it gives off the left carotid, and splits into the carotid and subclavian of the right side, then the left subclavian is sent off. So that neither here, properly speaking, is there an aorta ascendens, more than in the human; but this name has probably been imposed upon it from observing this in a cow, where indeed there is an ascending and descending aorta.

From this specialty of the distribution of the vessels of the right side, which happens, though not in so great a degree, in the human subject, we may perhaps in some measure account for the general greater strength, readiness, or facility of motion, which is observable in the right arm. Upon measuring the sides of the vessels, the surface of the united trunk of the right subclavian and nasal carotid is less than that of the left subclavian and carotid, as they are separated. If so, the resistance to the strength of blood must be less in that common trunk than in the left the right subclavian and carotid: But if the resistance be smaller, arm, leg, the absolute force with which the blood is sent from the heart being equal, there must necessarily be a greater quantity of blood sent through them in a given time; and as the strength of the muscles is, ceteris paribus, as the quantity of blood sent into them in a given time, those of the right arm will be stronger than those of the left. Now children, being conscious of this superior strength, use the right upon all occasions; and thus from use comes that great difference which is so observable. That this is a sufficient cause, seems evident from fact; for what a difference is there betwixt the right and the left arm of one who has played much at tennis? View but the arms of a blacksmith and legs of a footman, and you will soon be convinced of this effect arising from using them. But if by any accident the right arm is kept from action for some time, the other from being used gets the better; and those people are left-handed: For it is not to be imagined, that the small odds in the original formation of the vessels should be sufficient to resist the effect of use and habit (instances of the contrary occur every day); it is enough for our present argument, that where no means are used to oppose it, the odds are sufficient to determine the choice in favour of the right. Now because it is natural to begin with the leg corresponding to the hand we have most power of, this is what gives also a superiority to the right leg.

This difference is not peculiar to man, but is still more observable in those creatures in whom the same mechanism does obtain in a greater degree. Do but observe a dog at a trot, how he bears forward with his right side; or look at him when a scraping up any thing, and you will presently see that he uses his right much oftener than he does his left foot. Something analogous to this may be observed in horses. It has been the opinion of some anatomists, that left-handed people, as well as those distinguished by the name of ambidexter (who use both hands alike), have the two carotid and subclavian arteries coming off in four distinct distinct trunks from the arch of the aorta; but no appearance of this kind has ever been observed in such bodies as have been examined for this purpose; though indeed these have been but few, and more experience might throw greater light on the subject.

The diaphragm, in its natural situation, is in general more loose and free than the human; which is owing to its connexion with the neighbouring parts in a different manner from ours. The human diaphragm is connected to the pericardium; which again, by the intervention of the mediastinum, is tied to the sternum, spine, &c. but here there is some distance between the diaphragm and pericardium. We observe further, that its middle part is much more moveable, and the tendinous parts not so large. And indeed it was necessary their diaphragm should be somewhat loose, they making more use of it in difficult respiration than man. This we may observe by the strong heaving of the flanks of a horse or dog when out of breath; which corresponds to the rising of the ribs in us.

The sternum is very narrow, and consists of a great number of small bones, moveable every way; which always happens in creatures that have a great mobility in their spine. The ribs are straighter, and by no means so convex as the human; whereby in respiration, the motion forward will very little enlarge their thorax, which is compensated by the greater mobility of their diaphragm; so our thorax is principally enlarged according to its breadth and depth, and theirs according to its length. The want of clavicles, and the consequent falling in of the atlantal extremities upon the chest, may contribute somewhat to the straightness of the ribs.

We come next to discourse of those organs that serve for the secretion and excretion of urine. And first of the kidneys: Which in this animal are situated much in the same way as in the human subject; but have no fat on their inferior surface, where they face the abdomen, and are of a more globular form than the human. The reason of these differences will easily appear, if we compare their situation and posture in this animal with those in a man who walks erect. They are placed in them in the sacral part of the body, so are not subject to the pressure of the viscera, which seems to be the principal cause of the fatness of these organs in us, and perhaps may likewise be the cause of our being more subject to the stone than other animals. Hence there is no need of any cellular substance to ward off this pressure where there would necessarily be fat collected; but the atlantal part of their kidneys is pretty well covered with fat, lest they should suffer any compression from the action of the ribs and spine.

In the internal structure there is still more considerable difference: For the papillae do not here send out single the several tubuli uriniferi; but being all united, they hang down in form of a loose pendulous flap in the middle of the pelvis, and form a kind of partition; so that a dog has a pelvis formed within the substance of the kidney. The only thing that is properly analogous to a pelvis in man is that sac or dilatation of the ureters formed at the union of the ductus uriniferi. The external part of the kidney of a dog somewhat resembles one of the lobes of the kidney of a human fetus: but in a human adult the appearance is very different; because, in man, from the continual pressure of the surrounding viscera, the lobes, which in the fetus are quite distinct and separated, concrete, but the original cortical substance is still preserved in the internal parts of the kidney. The reason of these peculiarities may probably be, that the liquors of this animal, as of all those of the carnivorous kind, being much more acid than those that live on vegetable food, its urine must incline much to an alkalescency, as indeed the smell and taste of that liquor in dogs, cats, leopards, &c. evidently show, being fetid and pungent, and therefore not convenient to be long retained in the body. For this end it was proper that the secreting organs should have as little impediment as possible by pressure, &c. in the performing their functions; and for that design, the mechanism of their kidneys seems to be excellently adapted: We have most elegant pictures in Eustachius of the kidneys of brutes, delineated as such, with a view to show Vesalius's error in painting and describing them for the human.

The glandulae or capsules atrabiliariae are thicker and rounder than the human, for the same reason as the kidneys.

The ureters are more muscular than the human, because of the unfavourable passage the urine has through them; they enter the bladder near its large extremity.

The bladder of urine differs considerably from the bladder human; and first in its form, which is pretty much pyramidal or pyriform. This shape of the dog's bladder is likewise common to all quadrupeds, except the ape and those of an erect posture. In man it is by no means pyriform, but has a large sac at its dorsal and sacral part; this form depends entirely on the urine gravitating in our erect posture to its bottom, which it will endeavour to protrude; but as it cannot yield before, being contiguous to the os pubis, it will naturally stretch out, where there is the least resistance, that is, at the posterior and lateral parts; and were it not for this sac, we could not so readily come at the bladder to extract the stone either by the lesser or lateral operation of lithotomy. Most anatomists have delineated this wrong; so much, that we know of none who have justly painted it, excepting Mr Cowper, in his Myotomia, and Mr Butty. It has certainly been from observing it in brutes and young children, that they have been led into this mistake. The same cause, viz. the gravity of the urine, makes the bladder of a different form in brutes: In their horizontal position the neck, from which the urethra is continued, is higher than its fondus; the urine must therefore distend and dilate the most depending part by its weight.

As to its connection, it is fastened to the abdominal muscles by a process of the peritoneum, and that membrane is extended quite over it; whereas in us, its superior and posterior parts are only covered by it; hence in man alone the high operation of lithotomy can be performed without hazard of opening the cavity of the Why the abdomen. Had the peritoneum been spread over the human bladder in its whole extent, the weight of the viscera bladder but in our erect posture would have so borne upon it, that in part covered by they would not have allowed any considerable quantity the peritoneum to be collected there; but we must have been obliged. obliged to discharge its contents too frequently to be consistent with the functions of a social life: Whereas by means of the peritoneum, the urine is now collected in sufficient quantity, the viscera not gravitating this way.

It may be taken for a general rule, that those creatures that feed upon animal food have their bladder more muscular and considerably stronger and less capacious, than those that live on vegetables, such as horses, cows, swine, &c. whose bladder of urine is perfectly membranous, and very large. This is wisely adapted to the nature of their food: For in these first, as all their juices are more acid, so in a particular manner their urine becomes exalted; which, as its delay might be of very ill consequence, must necessarily be quickly expelled. This is chiefly effected by its stimulating this viscus more strongly to contract, and so to discharge its contents, though the irritation does not altogether depend upon the stretching, but likewise arises from the quality of the liquor. That a stimulus is one of the principal causes of the excretion of urine, we learn from the common saline diuretic medicines that are given, which are dissolved into the serum of the blood, and carried down by the kidneys to the bladder: The same appears likewise from the application of cantharides; or without any of these, when the parts are made more sensible, as in an excoriation of the bladder, there is a frequent desire to make water. Accordingly we find these animals evacuate their urine much more frequently than man, or any other creature that lives on vegetable food. And if these creatures, whose fluids have already a tendency to putrefaction, are exposed to heat or hunger, the liquids must for a considerable time undergo the actions of the containing vessels, and frequently perform the course of the circulation, without any new supplies of food; by which the fluids becoming more and more acid, the creature is apt to fall into feverish and putrid diseases.

Their spermatic vessels are within the peritoneum, which is spread over them, and from which they have a membrane like a mesentery, to hang loose and pendulous in the abdomen: whereas in us, they are contained in the cellular part of the peritoneum, which is tensely stretched over them. At their passage out of the lower belly, there appears a plain perforation, or holes; hence the adult quadruped, in this respect, resembles the human fetus. And from observing this in quadrupeds, has arisen the false notion of hernia or rupture among authors. This opening, which leads down to the testicle, is of no disadvantage to them, but evidently would have been to us; for from the weight of our viscera, and our continually gravitating upon these holes, we must have perpetually laboured under enterocoeles. This they are in no hazard of, since in them this passage is at the highest part of their belly; and in their horizontal posture, the viscera cannot bear upon it: And to prevent even the smallest hazard, there is a loose pendulous semilunar flap of fat, which serves two uses, as it both hinders the intestines from getting into the passage, and also the course of the fluids from being stopped in the vessels, which is secured in us by the cellular substance and tense peritoneum: And it may be worth while to observe, that this process remains almost unaltered, even after the animal has been almost exhausted of fat.

There is next a passage quite down into the cavity where the testicles lie. Had the same structure obtained in man, by the constant drilling down of the liquor which is secreted for the lubricating of the guts, we should always have laboured under an hydrocele; but their posture secures them from any hazard of this kind: indeed very fat lap-dogs, who consequently have an overgrown omentum, are sometimes troubled with an epiplocele.

The scrotum is shorter and not so pendulous as the Scrotum human in all the dog kind that want the vesiculae seminales, that the seed at each copulation might the sooner be brought from the testes, thus in some measure supplying the place of the vesiculae seminales; for the course of the seed through the vasa deferentia is thus considerably shortened by placing the secreting vessels nearer the males, to the excretory organs. Perhaps its passage is likewise quickened by the muscular power of the vasa deferentia, which is stronger in this creature than in man. The want of vesiculae seminales at the same time explains the reason why this creature is so tedious in copulation. But why these bodies are absent in the dog kind more than in other animals, is a circumstance we know nothing of.

The structure of the testicles is much the same with Testes the human; as are likewise the corpus pyramidae, varicoseum, or pampiniforme, and the epididymis or excretory vessel of the testicle. The vasa deferentia enter the abdomen where the blood vessels come out; and, passing along the upper part of the bladder, are inserted a little below the bulbous part of the urethra.

The prepuce has two muscles fixed to it: one that arises from the sphincter ani, and is inserted all along the penis; and this is called retractor praeputii: Penis. But the other, whose office is directly contrary to this, is cutaneous; and seems to take its origin from the muscles of the abdomen, or rather to be a production of their tunica carnea. The corpora cavernosa rise much in the same way as the human; but these soon terminate; and the rest is supplied by a triangular bone, in the inferior part of which there is a groove excavated for lodging the urethra. There are upon the penis two protuberant bulbous fleshy substances, resembling the glans penis in man, at the back of which are two veins, which by the erectores penis and other parts are compressed in the time of coition; and the circulation being stopped, the blood distends the large cavernous bodies. After the penis is thus swelled, the vagina Colliu by its contraction and swelling of its corpus cavernosum, which is considerably greater than in other animals, gripes it closely; and so the male is kept in action some time contrary to his will, till time be given for bringing a quantity of seed sufficient to impregnate the female: and thus, by that orgasmus veneris of the female organs, the want of the vesiculae seminales is in some measure supplied. But as it would be a very uneasy posture for the dog to support himself solely upon his hinder feet, and for the bitch to support the weight of the dog for so long a time; therefore, as soon as the bulbous bodies are sufficiently filled, he gets off and turns averse to her. Had, then, the penis been pliable as in other animals, the urethra must of necessity necessity have been compressed by this twisting, and consequently the course of the seed intercepted; but this is wisely provided against by the urethra's being formed in the hollow of the bone. After the emission of the seed, the parts turn flaccid, the circulation is restored, and the bulbous parts can be easily extracted.

The prostata seems here divided into two, which are proportionably larger than the human, and afford a greater quantity of that liquid.

The uterus of multiparous animals is little else but a continuation of their vagina, only separated from it by a small ring or valve. From the uterus two long canals mount upon the loins, in which the fetus are lodged: these are divided into different sacs, which are strongly constricted betwixt each fetus; yet these contractions give way in the time of birth. From these go out the tubae Fallopianae, so that the ovaria come to lodge pretty near the kidneys.

The disposition and situation of the mammae vary as they bear one or more young. Those of the uniparous kind have them placed between the sacral extremities, which in them is the highest part of their bodies, whereby their young get at them without the inconvenience of kneeling: Nevertheless, when the creatures are of no great size, and their breast large, as in sheep, the young ones are obliged to take this posture. In multiparous animals, they must have a great number of nipples, that their several young ones may have room at the same time, and these disposed over both thorax and abdomen; and the creatures generally lie down when the young are to be suckled, that they may give them the most favourable situation. From this it does not appear to be from any particular fitness of the vessels at certain places for giving a proper nourishment to the child, that the breasts are so placed in women as we find them, but really from that situation being the most convenient both for mother and infant.

Sect. III. Anatomy of ruminating Animals, and particularly of the Cow.

The animal whose structure we have been examining, being one of those which live chiefly on other animals, had a foot formed for running and seizing its prey. But the tribe of ruminating animals have their feet enveloped in a horny covering, fitting them for walking much, as is required of many of them, but totally disqualifying them for seizing living prey.

In these animals, the spinous processes of the vertebrae of the neck diminish in size according to the length of the neck; the atlas, or first vertebra, has its lateral processes flattened and bending forwards, and the mammillary processes of the back of the head are lengthened out; hence, they can move the head with difficulty sideways or forwards, but the motion of the neck is very extensive. The ribs are broad and thick. The scapula is narrow next the back, and lengthened out towards the neck, and it has neither acromion nor coracoid process. The great tuberosity near the head of the thigh bone, in the atlantal extremity is very large, and the rough line on the bone very prominent, to give greater room for the insertion of strong muscles. The two bones of the fore leg grow together almost their whole length, being only distinguished from it at the top by a furrow. Hence, the side motion of the foot in these animals is almost entirely prevented. The haunch bone is shaped something like a hammer, with the anterior part of the spine extremely large, and the muscles situated about these bones exceeding strong and bulky, as one would suppose they ought to be, in order to enable these animals to kick with greater power.

There are no parietal bones in the skull of these animals, but their place is occupied by one very strong bone in the top of the head; the frontal bone is very large, and forms a large arch overhanging each orbit.

The brain, in these animals, is much smaller in proportion to the rest of their body, than in man; in the ox it constitutes $\frac{1}{4}$ of the weight of the body, whereas in man it amounts to about $\frac{1}{5}$; its general form does not differ much from that of man.

In the eye of the cow the pupil is oblong, rounded at the ends, and the tapetum is of a beautiful green colour, changing to an azure blue; the striae at the back of the uvea are very large and conspicuous. The eye of this animal is usually the subject of dissection in examining the structure of this organ, which it exhibits to great advantage. It is in the organs of digestion, that these animals differ most essentially from the other mammalia; these therefore deserve a particular examination.

There are no cutting teeth in the upper jaw, but the history of the gums are pretty hard, and the tongue rough. This roughness is occasioned by long sharp-pointed papillae, with which the whole substance of it is covered. These papillae are turned towards the throat; so that by their means the food, having once got into the mouth, is not easily pulled back. The animals therefore supply the defect of teeth by wrapping their tongue round a tuft of grass: and so, pressing it against the upper jaw, keep it stretched, and cut it with the teeth of the under jaw; then, without chewing, throw it down into the gullet, which in these creatures consists of a double row of spiral fibres crossing one another. All animals which ruminate must have more stomachs than one; some have two, some three; our present subject has no less than four. The food is carried directly down into the first, which lies upon the stomachs left side, and is the largest of all: it is called ventriculus, and xystus, by way of eminence. It is what is called by the general name of paunch by the vulgar names. There are no rugae upon its internal surface; but instead of these there are a vast number of small blunt-pointed processes, by which the whole has a general roughness, and the surface is extended to several times the size of the paunch itself. The food, by the force of its muscular coat, and the liquors poured in here, is sufficiently macerated; after which it is forced up hence by the gullet into the mouth, and there it is made very small by mastication; this is what is properly called chewing the cud, or rumination; for which purpose the grinders are exceedingly well fitted: for instead of being covered with a thin crust, the enamel on them consists of perpendicular plates, between which the bone is bare, and constantly wearing faster than the enamel, so that the tooth remains good to extreme old age; and by means of these teeth the rumination is carried on for a long time without any danger of spoiling. After rumination, the food is sent down by the gullet into the second stomach; for the gullet opens indifferently into both. It ends exactly where the two stomachs meet; and there is a smooth gutter with rising edges which leads into the second stomach, from thence to the third, and also to the fourth: however, the creature has the power of directing it into which it will. Some tell us, that the drink goes into the second; but that might be easily determined by making them drink before slaughter.

The second stomach, which is the anterior and smaller, is called *reticulum*, *honeycomb*, the *bonnet* or *king's hood*. It consists of a great number of cells on its internal surface, of a regular pentagonal figure, like a honeycomb. Here the food is farther macerated; from which it is protruded into the third, called *omacium* or *omacium*, *vulgo* the *omacium*, because the internal surface rises up into a great many plicae or folds, and *stratum super stratum*, according to the length of this stomach. Some of these plicae are farther produced into the stomach than others; i.e., first two long ones on each side, and within these two shorter in the middle, &c. There are numberless glandular grains like millet seeds dispersed on its plicae, from which some authors call this stomach the *millet*. From this it passes into the fourth, whose names are *vesper*, *abomasum*, *caillie*, or the red, which is the name it commonly has because of its colour. This much resembles the human stomach, or that of a dog; only the inner folds or plicae are longer and looser; and it may also be observed, that in all animals there is only one digestive stomach, and that has the same coagulating power in the fetus as the fourth stomach in this animal; whence this might not improperly be called the only true stomach. *Caillie* signifies curdled; and hence the French have given that as a name to this fourth stomach, because any milk that is taken down by young calves is there curdled. It is this fourth stomach, with the milk curdled in it, that is commonly taken for making rennet: but after the bile and pancreatic juice enter, this coagulation is not to be found, which shows the use of these liquors. There are other creatures which use the same food, that have not such a mechanism in their digestive organs. Horses, asses, &c., have but one stomach, where grass is macerated, and a liquor for their nourishment extracted, and the remainder sent out by the anus very little altered. From this different structure of the stomach in these creatures, a ruminant animal will be served with one-third less food than another of equal bulk: graziers are sufficiently acquainted with this. The reason is, that ruminating animals have many and strong digestive organs; all their food is fully prepared, and almost wholly converted into chyle: But a horse's stomach is not fitted for this; so that he requires a much greater quantity of food to extract the same nourishment.

The guts of these creatures are of a considerable length in proportion to the bulk of the body; and this confirms what we said formerly on the subject of the intestines of a dog, viz., that the length and capacity of the guts were different in different animals, according to the nature of their food.

The *duodenum* is formed here much the same way as in a dog, and the general intention kept in view with regard to the mixture of the bile and pancreatic lymph.

The great guts here hardly deserve that name, their diameter differing very little from that of the small; but to compensate this, they are much longer proportionally than a dog's, being convoluted as the small guts are. The *cecum* is very large and long. The digestion of the cow, as well as some other animals, is accomplished with *ruminating*; the intention of which seems to be, that the food may be sufficiently comminuted, and thus more fully acted upon by the stomach: for it is not observed that a calf ruminates as long as it is fed only upon milk, though the action takes place as soon as it begins to eat solid food. But it is to be observed, that as long as a calf feeds only upon milk, the food descends immediately into the fourth stomach (which, as has been already mentioned, seems only capable of performing the operation of digestion) without stopping in any of the first three. The rumination does not take place till after the animal has eaten a pretty large quantity; after which she lies down, if she can do it conveniently, and begins to chew, though the operation will take place in a standing posture, if she cannot lie down. In this action a ball is observed to rise from the stomach with great velocity, almost as if shot from a musket. This ball the animal chews very accurately, and then swallows it again, and so on alternately, till all the food she has eaten has undergone this operation. This is easily explained from the structure of the gullet, which has one set of fibres calculated for bringing up the grass, and another for taking it down.

By means of rumination, the cow extracts a much larger proportions of nourishment from her food than those animals which do not ruminate; and hence she is contented with much worse fare, and smaller quantities of it, than a horse; hence also the dung of cows, being much more exhausted of its fine parts than horse-dung, proves much inferior to it as a manure.

The *spleen* differs not much either in figure or situation from that of a dog; but it is a little more firmly fixed to the diaphragm, there not being here so much danger of this viscus's being hurt in the flexions of the spleen.

The *liver* is not split into so many lobes in this creature as either in a man or dog; which depends on the small motion this creature enjoys in its spine, which made such a division needless. This also confirms what we formerly advanced on this head.

The situation of the *heart* is pretty much the same with that of a dog, only its point is rather sharper: In us, the heart beating continually against the ribs, and both ventricles going equally far down to the constitution of the apex, it is very obtuse: but here the apex is made up only of the left ventricle, so is more acute.

The *aorta* in this creature is justly divided into *ascending* and *descending*, though this division is ill founded either in a dog or man; and it has certainly been deduced from this subject that the older anatomists took their descriptions when they made this division; for here the aorta divides into two, the ascending and descending.

Their urinary bladder is of a pyramidal shape. It is Bladder. very large, and more membranaceous; for the urine of these creatures not being so acrid as that of carnivorous animals, there was no such occasion for expelling it so soon.

The male is provided with a loose pendulous scrotum, and consequently with vesiculae seminales. The female organs differ from those of a bitch, mostly as to the form of the cornua uteri, which are here contorted in form of a snail. In this, and all uniparous animals, they contain only part of the secundines; but in bitches, and other multiparous animals, they run straight up in the abdomen, and contain the fetus themselves.

The form of a cow's uterus differs from the human in having two pretty large cornua. This is common to it with other brutes; for a bitch has two long cornua uteri. But these again differ (as being multiparous and uniparous) in this, that in the bitch's cornua the fetus are contained; whereas here there is only part of the secundines, being mostly the allantois with the included liquor. The muscular fibres of the uterus are more easily discovered; its internal surface has a great number of spongy, oblong, protuberant, glandular bodies fixed to it. These are composed of vessels of the uterus terminating here. In an unimpregnated uterus we can easily press out of them a chylous mucilaginous liquor; they are composed of a great many processes or digituli, and deep caverns, answering to as many caverns and processes of the placenta. Their resemblance has occasioned the name of papillae to be given them; and hence it was that Hippocrates was induced to believe that the fetus sucked in utero. The papillae are found in all the different stages of life, in the various stages of pregnancy, and likewise in the unimpregnated state. It is not easy to determine whether the uterus grows thicker or thinner in the time of gestation. The membranes, it is plain (by the stretching of the parts), must be made thinner; but then it is as evident, that the vessels are at that time enlarged, upon which principally the thickness of any part depends; so there seems to be as much gained the one way as lost the other.

The os uteri is entirely shut up by a glutinous mucilaginous substance, that is common to the females of all creatures when with young: by this the external air is excluded, which would soon make the liquors corrupt: it also prevents the inflammation of the membranes, and the hazard of abortion. By this means also the lips of the womb are kept from growing together, which otherwise they would certainly at this time do. There are mucous glands placed here to secrete this gluten, which on the breaking of the membranes with the contained waters makes a soap that lubricates and washes the parts, and makes them easily yield. The first of the proper involucra of the fetus is the chorion.

The chorion is a pretty strong firm membrane, on whose external surface are depressed a great many red fleshy bodies of the same number, size, and structure, with the papillae, with which they are mutually indented. They have been called cotyledones, from κοτυληδών, "cavity." This is greatly disputed by some as a name very improper; but we think without reason, since the surface that is connected to the papillae is concave, though when separated it appears rather convex. To shun all dispute, they may be called properly enough placentule, since they serve the same use as the placenta in woman. The separation of these from the papillae without any laceration, and our not being able to inject coloured liquors from the vessels of the glands of the uterus into the placentule, seem to prove beyond a reply, that there can be here no anastomoses betwixt the vessels. On their coats run a great number of vessels that are sent to the present placentule, on the external side next to the uterus; whereas in creatures that have but one placenta, as in the human subject, cats, dogs, &c., the adhesion is somewhat firmer: The placentae are likewise joined to the papillae in the cornua uteri. We shall next give the history of the allantois.

This is a fine transparent membrane contiguous to Allantois, the former. It is not a general involucrum of the fetus in the mother, for it covers only a small part of the amnios. It is mostly lodged in the cornua uteri. In mares, bitches, and cats, it surrounds the amnios, being everywhere interposed betwixt it and the chorion. In sheep and goats it is the same as in this animal; and in swine and rabbits it covers still less of the amnios. This sac is probably formed by the dilatation of the urachus, which is connected at its other end to the fundus of the bladder, through which it receives its contents; and a great quantity of urine is commonly found in it. The membrane is doubled at the extremity of the canal, to hinder the return of the urine back into the bladder. Its vessels are so excessively fine and few, that we cannot force an injected liquor farther than the beginning of this coat. This membrane is so far analogous to the cuticula, as not to be liable to corruption, or easily irritated by acrid liquors. The existence of this membrane in women has been very warmly disputed on both sides. Those who are against its existence deny they could ever find it; and, allowing it were so, allege, that since the urachus is impervious, as the human bladder by our not being able to throw liquors from the allantois bladder into it, or vice versa, it cannot serve the use that is agreed by all it does serve in beasts; and therefore in the human body there is no such thing. But if we consider, on the other hand, first, that there seems to be the same necessity for such a reservoir in man as in other animals; secondly, that we actually find urine contained in the bladder of the human fetus; thirdly, that urine has been evacuated at the navel when the urethra was stopped, which urine without this conduit would have fallen into the cavity of the abdomen; fourthly, that midwives have pretended to remark two different sorts of waters come away at the time of birth; and, lastly, that Dr Littré and Dr Hale have given in this membrane of a human subject, with all the other secundines, curiously prepared, the one to the Royal Academy at Paris, the other to the Royal Society at London; by which societies their respective accounts are attested; not to mention Verheyen, Heister, Keill, &c. who affirm their having seen it; and Albinius is said to have shewn to his college every year a preparation of it: On all these accounts it seems most probable, that there is such a membrane in the human body.

The third proper integument of the fetus is the amnios. It is thinner and firmer than the chorion; it has numerous ramifications of the umbilical vessels spread upon it, the lateral branches of which separate a liquor into its cavity. This is the proper liquor of the amnios; CHAP. V. THE ANATOMY OF BIRDS.

Sect. I. Of Birds in General.

The structure of the greater part of these animals is obviously calculated for the most rapid of all motions. That part of the vertebral column which constitutes the back is immoveable; but the neck is exceedingly flexible, the vertebrae being articulated together, not by flat surfaces, but by portions of cylinders, but in such a manner as that the more atlantal vertebrae can move only forward, the more sacral only backward. The neck is generally long, but its length differs in various species, being determined by their manner of life and other circumstances. The head is small in proportion to the body, and generally ends in a sharp bill, that the animal may the more easily make its way through the air. The breast bone is shaped like a shield, and has in the middle a large and broad spine, like the keel of a ship, thus forming a considerable extent of surface for the insertion of muscles. This ridge is most conspicuous in birds that fly. On each side of the breast bone, next the wings, are two bones, which correspond to the clavicle or collar bone in man, by which the wings are connected to the breast bone, and between these is a very elastic bone with two horns, shaped like a V, and commonly known by the name of merry thought. The wings are composed in a manner similar to the atlantal extremity in the mammalia, and are generally divided into two portions; the wing, to which the principal muscles are attached, and the pinion.

Fowls have the strongest muscles of their whole bodies, but a good deal farther forwards; whence it would at first view appear, that their heads would be erect, and their posterior parts most depending when raised in the air; but by stretching out their heads which act upon the lever of a long neck, they alter their centre of gravity pretty much; and also by filling the sacs or bladders in the inside of their abdomen with air, and expanding their tail, they come to make the posterior part of their bodies considerably higher; and thus they fly with their bodies nearly in a horizontal situation. Hence we find, that if their necks are kept from being stretched out, or if you cut away their tails, they become incapable of flying any considerable way.

The largeness of the wings in different fowls varies according to the wants of the creature. Thus birds of prey, who must fly a considerable way to provide their food, have large strong wings; whereas domestic birds, who find their nourishment almost everywhere, have very short and but small wings. Their tail is of use in assisting to raise them in the air; though the chief purpose of it is to serve as a rudder in guiding their flight, whilst they use their wings as we do oars in putting forward a boat. The best account of this manner of progression of fowls is given by Alfonso Borellus, in his treatise De Motu Animalium; and in the Religious Philosopher we have Borelli's doctrine stripped pretty much of its mathematical form. The sacral extremities are situated so far back, as to make us at first think they would be in continual hazard of falling down forwards when they walk: but this is prevented by their holding up their head and neck, so as to make the centre of gravity fall upon the feet; and when they have occasion for climbing up a steep place, they stretch out their heads and necks forward, especially if they are short-legged, the better to preserve properly the balance of the body. Thus we may observe a goose entering a barn door, where generally there is an ascending step, to stretch out its neck, which before was raised, and incline its body forwards. This is laughed at by the common people, who ascribe it to a piece of folly in the goose, as if afraid of knocking its head against the top of the door.

Carnivorous birds are provided with strong crooked claws for catching their prey; water fowls use them for swimming; and, principally for this purpose, they have a strong firm membrane interposed betwixt the toes. There is a beautiful mechanism to be observed in the toes of fowls, which is of considerable use to them. For their toes are naturally drawn together, or bend, when the foot is bended: this is owing to the shortness of the tendons of the toes, which pass over them, which is analogous to our heel; and that the toes are set in the circumference of a circle, as our fingers are: Hence, when the foot is bended, the tendons must consequently be much stretched; and, since they are inserted into the toes, must of necessity bend them when the foot is bended; and when the foot is extended, the flexors of the toe are again relaxed, and they are therefore expanded. This is also of great use to different kinds of fowls; thus the hawk descending... scending with his legs and feet extended, spreads his talons over his prey; and the weight of his body bending his feet, the toes are contracted, and the prey is seized by the talons. This is also of great use to water fowls: for had there been no such contrivance as this, they must have lost as much time when they pulled their legs in as they had gained by the former stroke: but, as the parts are now framed, whenever the creature draws in its foot, the toes are at the same time bended and contracted into less space, so that the resistance made against the water is not near so great as before: on the contrary, when they stretch their feet, their toes are extended, the membrane betwixt them expanded, and consequently a greater resistance made to the water. Again, such fowls as live mostly in the air, or have occasion to sustain themselves on branches of trees in windy weather, and even in the night-time when asleep, while all their muscles are supposed to be in a state of relaxation, have only to lean down the weight of their bodies, and their toes continue bended without any muscles being in action; and whenever they would disentangle themselves, they raise up their bodies, by which their feet, and consequently their toes, are extended.

Fowls have a particular covering of feathers different from all other creatures, but exactly well suited to their manner of life: for it not only protects them from the injuries of the weather, but serves them in their progression through that thin aerial element they are, for the most part, employed in; and as fowls live much in the water, their feathers being continually besmeared with an oily liquor, keeps the water from soaking into their skins, and so prevents the bad effects which it would infallibly otherwise produce.

The brain in birds is large in proportion to their heads: it has neither corpus callosum, fornix, nor corpora quadrigemina. Hence we may conclude, that these parts are not essential to life, nor probably to reason.

The organ of smelling is placed at the base of the beak; the nostrils are sometimes naked, sometimes concealed by feathers, and by a small scale, or even by a fleshy substance.

The organ of smelling is very large, and well provided with nerves; hence they have this sensation very acute. Ravens and other birds of prey give a sure proof of this, by their being able to find out their prey, though concealed from their sight and at a considerable distance.

Those birds that grope for their food in the waters, mud, &c. have large nerves, which run quite to the end of their bills, by which they find out and distinguish their food.

The anterior part of their eyes (instead of having the sclerotic coat continued, so as to make near a sphere as in us) turns all of a sudden flat: so that here the sclerotic makes but half a sphere; and the cornea rises up afterwards, being a portion of a very small and distinct sphere: so that in these creatures there is a much greater difference betwixt the sclerotic and cornea than in us. Hence their eyes do not jut out of their heads, as in man and quadrupeds. As most of these creatures are continually employed in hedges and thickets, therefore, that their eyes might be secured from these injuries, as well as from too much light when flying in the face of the sun, there is a very elegant mechanism in their eyes. A membrane rises from the internal canthus, which at pleasure, like a curtain, can be made to cover the whole eye; and this by means of a proper muscle that rises from the sclerotic coat, and passing round the optic nerves, runs through the musculus oculi attollens (by which however the optic nerves are not compressed) and palpebra, to be inserted into the edge of this membrane. Whenever this muscle ceases to act, the membrane by its own elasticity again discovers the eye. This covering is neither pellucid nor opaque, both which would have been equally inconvenient; but, being somewhat transparent, allows as many rays to enter as to make any object just visible, and is sufficient to direct them in their progression. By means of this membrane it is that the eagle is said to look at the sun.

Besides, all birds have another peculiarity, the use Bourie of which is not so well understood: and that is, a noir. Its pretty long black triangular purse, rising from the bottom of their eye just at the entry of the optic nerve, and stretched out into their vitreous humour, and one would imagine it gave some threads to the crystalline. To this the French (who probably were the first who took notice of it in their dissections before the Royal Academy) gave the name of bourie noir. This may probably serve to suffocate some of the rays of light, that they may see objects more distinctly without hurting their eyes. It has a connection with the vitreous, and seems to be joined also to the crystalline humour. If we suppose it to have a power of contraction (which may be as well allowed as that of the iris), it may so alter the position of the vitreous and crystalline humours, that the rays from any body may not fall perpendicularly upon the crystalline: and this seems to be necessary in them, since they cannot change the figure of the anterior part of their eye so much as we can do: and as this animal is exposed often to too great a number of rays of light, so they have no tapetum, but have the bottom of their eye wholly black on the retina; and in consequence of this, fowls see very ill in the dark.

They have no external ear; but in place of it a tuft of very fine feathers covering the meatus auditorius, which easily allows the rays of sound to pass them, and likewise prevents dust or any insect from getting in. An external ear would have been inconvenient in their passing through thickets, and in flying, &c. A liquor is separated in the external part of the ear, or meatus auditorius, to lubricate the passage, and further prevent the entrance of any insects, &c. The membrana tympani is convex externally; and no muscles are fixed to the bones of their ear, which are rather of a cartilaginous consistence: any tremulous motions impressed on the air are communicated in these creatures merely by the spring and elasticity of these bones; so probably, the membrane is not so stretched as in the human ear by muscles. The semicircular canals are very distinct, and easily prepared.

The rostrum, bill, or beak of fowls, is composed of the variety two mandibles; and, as in quadrupeds, the upper one in the beaks has no motion but what it possesses in common with the head. But parrots are an exception to this rule; for they can move the upper mandible at pleasure: that is exceedingly convenient, as it enables them to lay hold of whatever comes in their way. Carnivorous fowls...

Of Birds. Fowls have their beaks long, sharp, and crooked; the domestic fowls, such as the hen kind, &c., have strong short beaks, commodiously fitted to dig up and break their food; the water-fowls, again, have long or very broad scoop-like beaks, which is most convenient for them.

The other circumstances in which the structure of birds differs from that of other animals, particularly as to the organs of digestion, respiration, and generation, will be best explained by describing them in an individual instance; and we shall select for this purpose the domestic cock, taking an opportunity of contrasting the viscera of a carnivorous bird with those of this species as a granivorous bird.

Sect. II. Anatomy of a Cock.

Though this kind of birds live upon food somewhat similar to that of man, yet as they have no teeth to separate or break down this food, we should expect to find something to compensate for the want of teeth, something remarkable in the organs of digestion; we shall therefore begin with these parts.

The gullet of this creature runs down its neck, somewhat inclined to the right side; and terminates in a pretty large membranous sac, which is the ingluvies or crop, where the food is macerated and dissolved by a liquor separated by the glands, which are easily observed everywhere on the internal surface of this bag. The effect of this maceration may be very well observed in pigeons, who are sometimes in danger of being suffocated by the pease, &c., they feed upon, swelling to such an immense bulk in their ingluvies, that they can neither get upwards nor downwards. If it be a favourite fowl, it might be preserved by opening the sac, taking out the pease, and sewing up the wound.

The food getting out of this sac goes down by the remaining part of the gullet into the ventriculus succenturiatus, or infundibulum Peyeri, which is a continuation of the gullet with more numerous glands, which separate a liquor to dilute the food still more, which at length gets into the true stomach or gizzard, ventriculus callosus, which consists of two very strong muscles covered externally by a tendinous aponeurosis, and lined on the inside by a very thick firm membrane, which we evidently discover to be a production of the cuticle. This might have been proved in some measure a priori, from taking notice, that this membrane, which in chicks is only a thin slight pellicle, by degrees turns thicker and stronger the more attrition it suffers; but there is no other animal substance, so far as we know, which grows more hard and thick by being subjected to attrition, excepting the cuticle.

Hence may be drawn some kind of proof of what has been affirmed concerning the tunica villosa of the stomach and intestines in the human body, viz., that it was in part a continuation of the epidermis; nay, all the hollow parts of the body, even arteries, veins, &c., seem to be lined with a production of this membrane, or one analogous to it. The use of the internal coat of the stomach of fowls is to defend the more tender parts of that viscus from the hard grains and little stones those creatures take down. The use of the gizzard is to compensate for the want of teeth; and it is well fitted for this purpose, from the great strength of which it possesses.

The digestion of these animals is performed merely by attrition, as is evinced by many experiments; and it is further assisted by the hard bodies they swallow. We see them daily take down considerable numbers of the most solid rugged little flints they find; and these can serve for no other purpose than to help the trituration of their aliments. After these pebbles, by becoming smooth, are unfit for this office, they are thrown up by the mouth. Hence fowls that are long confined, though ever so well fed, turn lean for want of these stones to help their digestion. This was put beyond all dispute by Mr Tavvy, who gave a piece of metal to an ostrich, convex on one side and concave on the other, but carved on both; and opening the creature's body some time after, it was found, that the carving on the convex side was all obliterated, while the engraved character remained the same as before on the concave side, which was not subjected to the stomach's pressure: which could not have happened had digestion been performed by a menstruum, or any other way whatsoever; but may be easily solved by allowing a simple mechanical pressure to take place. We are, however, by no means to conclude from this, as some have too rashly done, that in the human body digestion is performed by simple attrition; otherwise we may, with equal strength of reason, by as good arguments drawn from what is observed in fishes, prove that the aliments are dissolved in our stomachs by the action of a menstruum. But this method of reasoning is very faulty; nor can it ever bring us to the true solution of any philosophical or medical problem. It is very plain, since the structure of the parts of the human stomach are so very different from that of this creature, that it is foolish and unreasonable to imagine both of them capable of producing the same effects. At each end of the stomach, there are as it were two particular sacs of a different texture from the rest of the stomach, not consisting of strong muscular fibres; they seem to be receptacles for the stones (especially at the end which is farthest from the orifice), while the digested aliment is protruded into the intestines.

Spallanzani, however, has lately found, that pebbles are not at all necessary to the trituration of the food of these animals. At the same time, he does not deny, that when put in motion by the gastric muscles, they are capable of producing some effect on the contents of the stomach; but is inclined to believe, that they are not sought for and selected by design, as many suppose, but because they frequently happen to be mixed with the food.

The duodenum begins pretty near the same place at Duodenum which the gullet enters; yet notwithstanding the vicinity of these two tubes, the aliments are in no danger of getting out before they are perfectly digested, by reason of a protuberance betwixt the orifices; and in those creatures who have such a strong muscular stomach, it is a matter of great indifference whether the entry of the gullet or pylorus be highest, provided that the entry from the gullet does not allow the food to regurgitate, since the force of the stomach can easily protrude it towards the duodenum. This gut is mostly in the right side, and hangs pendulous in their abdomen, having having its two extremities fixed to the liver. The ductus cholecodochus enters near its termination, where it mounts up again to be fixed to the liver; and lest, by the contraction of the intestines, the bile should pass over without being intimately blended with the chyle, that duct enters downwards, contrary to the course of the food, and contrary to what is observed in any of the animals we have yet mentioned. But still the general intention is kept in view, in allowing these juices the fairest chance of being intimately blended with the food.

The small guts are proportionally longer than those of carnivorous birds, for the general cause already assigned. At the end of the ilium they have two large intestina ceca, one on each side, four or five inches long, coming off from the side of the rectum, and ascending; and we find them containing part of the food. These serve as reservoirs to the feces; which, after some delay there, regurgitate into what soon becomes the rectum; which, together with the excretories of urine and organs of generation, empties itself into the common cloaca. The small intestines are connected by a long loose mesentery, which has little or no fat accompanying the blood vessels, there being no hazard of the blood's being stopped.

The principal difference to be observed in carnivorous birds is in their chylopoietic viscera, which may be accounted for from their different way of life.

Immediately under their clavicles, you will observe the oesophagus expanded into their inguivies, which is proportionally less than in the granivorous kind, since their food does not swell so much by maceration; and for the same reason, there is a less quantity of a menstrum to be found here.

They have also a ventriculus succenturiatus, plentifully stored with glands, situated immediately above their stomach, which we see here is thin and muscular-membranous, otherwise than in the granivorous kind; and this difference, which is almost the only one we shall find betwixt the two different species of fowls, is easily accounted for from the nature of their food, which requires less attrition, being easier of digestion than that of the other kind; nevertheless, it seems requisite it should be stronger than the human, to compensate the want of abdominal muscles, which are here very thin.

The same mechanism obtains in this creature's duodenum that we have hitherto observed. As being a carnivorous animal, its guts are proportionally shorter than those of the granivorous kind: for the reason first given, viz. its food being more liable to corrupt, therefore not proper to be long detained in the body; and for that reason it has no intestina ceca, of which the other species of fowls have a pair. The difference in their wings, backs, and claws, is obvious; and has been already in some measure observed.

The pancreas in this creature lies betwixt the two folds of the duodenum, and sends two or three ducts into this gut pretty near the biliary.

The spleen is here of a round globular figure, situated between the liver and stomach; and betwixt these and the back bone it enjoys the same properties as in other animals, viz. large blood vessels, &c. All its blood is sent into the vena portarum, and has a perpetual conguassation. It has no excretory, as far as we know. Their liver is divided into two equal lobes by a pellucid membrane, running according to the length of their body: and hence we may observe, that it is not peculiar to that bowel to lie on the right side; which is still more confirmed by what we observe in fishes, where the greatest part of it lies in the left side.

The shape of their gall bladder is not much different from that of quadrupeds; but is thought to be longer, in proportion to the size of the animal, and is farther removed from the liver.

The principal difference to be remarked in their heart, is the want of the valvulae tricuspides, and their place being supplied by one fleshy flap.

The lungs are not loose within the cavity of the thorax, but fixed to the bone all the way; neither are their structures divided into lobes, as in those animals that have a more and larger motion in their spine. They are two red spongy bodies, covered with a membrane that is pervious, and which communicates with the larger vesicles or air-bags that are dispersed over the whole abdomen; which vesicles, according to Dr Monro, serve two very considerable uses. The one is to render their bodies specifically light, when they have a mind to ascend and buoy themselves up when flying, by distending their lungs with air, and also straiten their windpipe, and so return the air. Secondly, They supply the place of a muscular diaphragm and strong abdominal muscles; producing how the same effects on the several contained viscera, as these plied muscles would have done, without the inconvenience of their additional weight; and conducing as much to the exclusion of the egg and feces.

Dr Hunter has made some curious discoveries relative to these internal receptacles of air in the bodies of birds. Some of them are lodged in the fleshy parts, and some in the hollow bones; but all of them communicate with the lungs. He informs us, that the air cells which are found in the soft parts have no communication with the cellular membrane which is common to birds as well as other animals. Some of them communicate immediately with each other; but all of them by the intervention of the lungs as a common centre. Some of them are placed in cavities, as the abdomen; others in the interstices of parts, as about the breast. The bones which receive air are of two kinds; some of them divided into innumerable cells; others hollowed out into one large canal. They may be distinguished from such as do not receive air, by having less specific gravity; by being less vascular; by containing little oil; by having no marrow nor blood in their cells; by having less hardness and firmness than others; and by the passage for the air being perceivable.

The mechanism by which the lungs are fitted for conveying air to these cavities is, their being attached to the diaphragm, and connected also to the ribs and sides of the vertebrae. The diaphragm is perforated in several places by pretty large holes, allowing a free passage of air into the abdomen. To each of these holes is attached a distinct membranous bag, thin and transparent. The lungs open at their interior part into membranous cells, which lie upon the side of the pericardium, and communicate with the cells of the sternum. The superior parts of the lungs open into cells of a loose net-work, through which the windpipe and gullet pass. When these cells are distended with with air, it indicates passion, as in the case of the turkey-cock, pouting-pigeon, &c.

These cells communicate with others in the axilla, and under the large pectoral muscle; and those with the cavity of the os humeri, by means of small openings in the hollow surface near the head of that bone. Lastly, The posterior edges of the lungs have openings into the cells of the vertebrae, ribs, os sacrum, and other bones of the pelvis, from which the air finds a passage to the cavity of the thigh bone.

Concerning the use of these cavities the doctor conjectures, that they are a kind of appendage to the lungs; and that, like the bags continued through the bellies of amphibious animals, they serve as a kind of reservoirs of air. They assist birds during their flight, which must be apt to render frequent respiration difficult. He farther insinuates, that this construction of the organs of respiration may assist birds in singing; which, he thinks, may be inferred from the long continuance of song between the breathings of a canary bird. On tying the windpipe of a cock, the animal breathed through a canula introduced into his belly; another through the os humeri, when cut across; and a hawk through the os femoris. In all these cases the animal soon died. In the first, the doctor ascribes the death to an inflammation of the bowels; but in the last, he owns it was owing to difficult breathing. What took place, however, was sufficient to show that the animals did really breathe through the bone.

When we examine the upper end of the trachea, we observe a rima glottidis with muscular sides, which may act in preventing the food or drink from passing into the lungs; for there is no epiglottis as in man and quadrupeds.

The windpipe, near where it divides, is very much contracted; and their voice is principally owing to this concretion. If you listen attentively to a cock crowing, you will be sensible that the noise does not proceed from the throat, but deeper; nay, this very pipe, when taken out of the body, and cut off a little after its division, and blown into, will make a squeaking noise something like the voice of these creatures. On each side, a little higher than this contraction, there is a muscle arising from the sternum, which dilates the trachea. The cartilages, of which the pipe is composed in this animal, go quite round it; whereas in man and quadrupeds they are discontinued for about one-fourth on the back part, and the intermediate space is filled up by a membrane. Neither is the trachea so firmly attached to their vertebrae as in the other creatures we have examined. This structure we shall find of great service to them, if we consider, that had the same structure obtained in them as in us, their breath would have been in hazard of being stopped at every flexion or twisting of the neck, which they are frequently obliged to. This we may be sensible of by bending our necks considerably on one side, upon which we shall find a great straitness and difficulty in breathing; whereas their trachea is better fitted for following the flexions of the neck by its loose connexion to the vertebrae.

In place of a muscular diaphragm, this creature has nothing but a thin membrane connected to the pericardium, which separates the thorax and abdomen. But besides this, the whole abdomen and thorax are divided by a longitudinal membrane or mediastinum connected to the lungs, pericardium, liver, stomach, and to the fat lying over their stomach and guts, which is analogous to an omentum, and supplies its place.

The lymphatic system in birds consists, as in man, of lympho-lacteal and lymphatic vessels, with the thoracic duct.

The lacteals, indeed, in the strictest sense, are the lymphatics of the intestines; and, like the other lymphatics, carry only a transparent lymph; and instead of one thoracic duct, there are two, which go to the jugular veins. In these circumstances, it would seem that birds differ from the human subject, so far at least as we may judge from the dissection of a goose, the common subject of this inquiry, and from which the following description is taken.

The lacteals run from the intestines upon the mesenteric vessels: those of the duodenum pass by the side of the pancreas; afterward they get upon the celiac artery, of which the superior mesenteric is a branch. Here they are joined by the lymphatics of the liver, and then they form a plexus which surrounds the celiac artery. Here also they receive a lymphatic from the gizzard, and soon after another from the lower part of the gullet. At the root of the celiac artery they are joined by the lymphatics from the glandulae renales, and near the same part by the lacteals from the other small intestines, which vessels accompany the lower mesenteric artery; but, before they join those from the duodenum, receive from the rectum a lymphatic, which runs from the blood vessels of that gut. Into this lymphatic some small vessels from the kidneys seem to enter at the root of the celiac artery. The lymphatics of the sacral extremities probably join those from the intestines. At the root of the celiac artery and contiguous part of the aorta, a net-work is formed by the vessels above described. From this net-work arise two thoracic ducts, of which one lies on each side of the spine, and runs obliquely over the lungs to the jugular vein, into the inside of which it terminates, nearly opposite to the angle formed by this vein and the subclavian one. The thoracic duct of the left side is joined by a large lymphatic, which runs upon the gullet. The thoracic ducts are joined by the lymphatics of the neck, and probably by those of the wings, where they open into the jugular veins. The lymphatics of the neck generally consist of two large branches, on each side of the neck, accompanying the blood vessels; and these two branches join near the lower part of the neck, and form a trunk which runs close to the jugular vein, and opens into a lymphatic gland; from the opposite side of this gland a lymphatic comes out, which ends in the jugular vein.

On the left side, the whole of this lymphatic joins the thoracic duct of the same side; but, on the right one, part of it goes into the inside of the jugular vein a little above the angle; while another joins the thoracic duct, and with that duct forms a common trunk, which opens into the inside of the jugular vein, a little below the angle which that vein makes with the sub-clavian. This system in birds differs most from that of quadrupeds, in the chyle being transparent and colourless, and in there being no visible lymphatic glands, neither in the course of the lacteals, nor in that of the lymphatics of the abdomen, nor near the thoracic ducts. The kidneys lie in the hollow excavated in the side of the back-bone, from which there is sent out a bluish coloured canal running along by the side of the vasa deferentia, and terminating directly in the common cloaca. This is the ureter, which opens by a peculiar aperture of its own, and not at the penis. Fowls having no urinary bladder, it was thought by some they never passed any urine, but that it went to the nourishment of the feathers; but this is false; for that whitish substance that we see their greenish feces covered with, and which turns afterwards chalky, is their urine. Let us next consider the organs of generation of both sexes, and first those of the male.

The testicles are situated one on each side of the back-bone; and are proportionally very large to the creature's bulk. From these run out the vasa seminifera; at first straight; but after they recede farther from the body of the testicle, they acquire an undulated or convoluted form, as the epididymis in man. These convolutions partly supply the want of vesiculae seminales, their coition being at the same time very short; These terminate in the penis, of which the cock has two, one on each side of the common cloaca, pointing directly outwards. They open at a distance from each other, and are very small and short; whence they have escaped the notice of anatomists, who have often denied their existence. In birds there is no prostate gland. This is what is chiefly remarkable in the organs of the male.

The racemus vitellorum, being analogous to the ovaria in the human subject, is attached by a proper membrane to the back-bone. This is very fine and thin, and continued down to the uterus. Its orifice is adverse with respect to the ovaria; yet notwithstanding, by the force of the organum veneris, it turns round and grasps the vitellus, which in its passage through this duct, called the infundibulum, receives a thick gelatinous liquor, secreted by certain glands. This, with what it receives in the uterus, composes the white of the egg. By this tube then it is carried into the uterus. The shell is lined with a membrane; and in the large end there is a bag full of air, from which there is no outlet.

The uterus is a large bag, placed at the end of the infundibulum, full of wrinkles on its inside; here the egg is completed, receiving its last involucrum, and is at last pushed out at an opening on the side of the common cloaca. From the testes in the male being so very large in proportion to the body of the creature, there must necessarily be a great quantity of semen secreted; hence the animal is salacious, and becomes capable of impregnating many females. The want of the vesiculae seminales is in some measure supplied by the convolutions of the vasa deferentia, and by the small distance betwixt the secreting and excretory organs. The two penes contribute also very much to their short coition; at which time the opening of the uterus into the cloaca is very much dilated, that the effect of the semen on the vitelli may be the greater.

A hen will of herself indeed lay eggs; but these are not impregnated, and yet appear entirely complete, except that the small black spot, which comes afterwards to be the rudiments of the chick, is not here to be observed.

### TABLE of the Proportional Number of Ribs and Vertebrae in various species of Birds

| Species | Verteb. of Neck | Verteb. of Back | Anter. false Ribs | True Ribs | Poster. false Ribs | No. of Ribs | Sacral Verteb. | Coccyg. Verteb. | |------------------|-----------------|-----------------|-------------------|-----------|-------------------|-------------|---------------|----------------| | Vultur. Vulture | - | 13 | 7 | - | - | 11 | 7 | | | Falco fulvus. Eagle | - | 13 | 8 | 0 | 7 | 0 | 7 | 17 | | haliaetus. Bald buzzard | - | 14 | 8 | 0 | 7 | 1 | 8 | 11 | | buteo. Buzzard | - | 11 | 7 | - | - | - | - | 10 | | nisus. Sparrow hawk | - | 11 | 8 | - | - | - | - | 11 | | milvus. Kite | - | 12 | 8 | - | - | - | - | 11 | | Strix ulula. Owl | - | 11 | 8 | - | 7 | - | - | 11 | | Muscicapa grisola. Fly-catcher | - | 10 | 8 | - | - | - | - | 10 | | Turdus merula. Black-bird | - | 11 | 8 | - | - | - | - | 10 | | Tanagra taldo. Tanagra | - | 10 | 8 | - | - | - | - | 9 | | Corvus corone. Crow | - | 13 | 8 | 1 | 5 | 1 | 7 | 13 | | pica. Magpie | - | 13 | 8 | 1 | 5 | 1 | 7 | 13 | | glandarius. Jay | - | 12 | 7 | 1 | 5 | 1 | 7 | 11 | | Sturnus vulgaris. Starling | - | 10 | 8 | 1 | 5 | 1 | 7 | 10 | | Loxia cocothraustes. Grosbeak | - | 10 | 7 | - | - | - | - | 12 | | pyrrhula. Bullfinch | - | 10 | 6 | - | - | - | - | 11 | | Fringilla domestica. Sparrow | - | 9 | 9 | 1 | 5 | 1 | 7 | 10 | | carduelis. Goldfinch | - | 11 | 8 | 1 | 5 | 1 | 7 | 11 | | Parus major. Titmouse | - | 11 | 8 | 6 | 6 | 1 | 7 | 11 | | Alauda arvensis. Lark | - | 11 | 9 | 1 | 5 | 1 | 7 | 10 |

TABLE ### TABLE, &c. continued.

| Species | Verteb. of Neck | Verteb. of Back | Anter. false Ribs | True Ribs | Poster false Ribs | No. of Ribs | Sacral Verteb. | Coccyg. Verteb. | |--------------------------|----------------|----------------|------------------|-----------|------------------|-------------|----------------|----------------| | Motacilla rubecula. | 10 | 8 | - | - | - | - | 10 | 8 | | Hirundo urbica. | 11 | 8 | - | - | - | - | 11 | 9 | | Caprimulgus europaeus. | 11 | 8 | - | - | - | - | 11 | 8 | | Trochilus pella. | 12 | 9 | - | - | - | - | 9 | 8 | | Upupa epops. | 12 | 7 | - | - | - | - | 10 | 7 | | Alcedo ispis. | 12 | 7 | - | - | - | - | 8 | 7 | | Picus viridis. | 12 | 8 | 1 | 6 | 1 | 8 | 10 | 9 | | Ramphastos. | 12 | 8 | - | - | - | - | 12 | 7+ | | Psittacus crithacus. | 12 | 9 | - | - | - | - | 11 | 8 | | Columba caesar. | 13 | 7 | 1 | 5 | 1 | 6 | 13 | 7 | | Pavo cristatus. | 14 | 7 | - | - | - | - | 12 | 8 | | Phasianus colchicus. | 13 | 7 | 2 | 8 | 1 | 11 | 15 | 5 | | Meleagris gallo-pavo. | 15 | 7 | - | - | - | - | 10 | 5 | | Crox nigra. | 15 | 8 | 2 | 4 | 1 | 7 | 10 | 7 | | Struthio camelus. | 18 | 8 | - | - | - | - | 20 | 9 | | Cassarurus. | 15 | 11 | - | - | - | - | 19 | 7 | | Phoenicopterus. | 18 | 7 | - | - | - | - | 12 | 7 | | Ardea cinerea. | 18 | 7 | 1 | 7 | - | 8 | 10 | 7 | | alba. | 19 | 7 | - | - | - | - | 11 | 8 | | grus. | 19 | 9 | 1 | 7 | 1 | 9 | 12 | 7 | | Platalea alba. | 17 | 7 | - | - | - | - | 14 | 8 | | Recurvirostra. | 14 | 9 | - | - | - | - | 10 | 8 | | Charadrius placidus. | 15 | 8 | 1 | 6 | 1 | 8 | 10 | 7 | | Tringa vanellus. | 14 | 8 | - | - | - | - | 10 | 7 | | Scolopax rusticata. | 18 | 7 | - | - | - | - | 13 | 8 | | arquata. | 13 | 8 | - | - | - | - | 10 | 8 | | Haematopus ostralegus. | 12 | 9 | - | - | - | - | 15 | 0 | | Rallus crex. | 13 | 8 | - | - | - | - | 13 | 8 | | Fulica atra. | 15 | 9 | - | - | - | - | 7 | 8 | | Parra. | 14 | 8 | - | - | - | - | 12 | 7 | | Pelicanus onocratalus. | 16 | 7 | - | - | - | - | 14 | 7 | | carbo. | 16 | 9 | - | - | - | - | 14 | 8 | | Sterna hirundo. | 14 | 8 | - | - | - | - | 10 | 8 | | Procellaria. | 14 | 8 | - | - | - | - | ?? | 8 | | Anas cygnus. | 23 | 11 | 2 | 8 | 1 | 11 | 14 | 8 | | anser. | 15 | 10 | - | - | - | - | 14 | 7 | | bernicla. | 18 | 10 | - | - | - | - | 14 | 9 | | boschas. | 14 | 8 | - | - | - | - | 14 | 7 | | tadorna. | 16 | 11 | - | - | - | - | 11 | 9 | | nigra. | 15 | 9 | - | - | - | - | 14 | 7 | | Mergus merganser. | 15 | 8 | 2 | 6 | 1 | 9 | 13 | 7 | | Colymbus cristatus. | 14 | 10 | - | - | - | - | 13 | 7 |

### CHAP. VI. ANATOMY OF REPTILES.

#### Sect. I. Of Reptiles in general.

These animals, like the fishes, have their blood nearly of the same temperature with the element in which they live. They have indeed a lung, and respire air; but their pulmonary vessels are only branches of the large general artery and vein, and do not, as in the hot-blooded animals, form a peculiar system equal to the vascular system of the rest of the body.

With respect to their organs of motion, reptiles may be divided into two orders. In the one, the serpents, the body is cylindrical and entirely without limbs: their motion is a kind of writhing or creeping.

The others have four feet very similar in structure to those of the mammalia, whence these animals have been called oviparous quadrupeds. Such of them as live in the water have frequently membranes between their toes, which they employ like the fins of fishes for swimming. One species has a kind of membranaceous Reptiles, branchless wings. We know two species which are called bipedal reptiles, which are only distinguished from serpents, in having two very small feet. In the whole class the feet are so short, and so close to the body, that they are not unaptly termed reptiles or creeping animals.

Their eyes are large and fiery, and are furnished with three lids. Their ear has neither concha nor external passage, and its tympanum lies flat to the head, and is often covered with scales or flesh; internally it has only one little bone composed of a plate furnished with a sort of handle. In some species the tympanum and its little bone are entirely wanting, as also the cochlea; but they have all semicircular canals, and a vestibule. Their nostrils are generally small. In the serpents, whose tongue is almost horny, the sense of taste cannot be very exquisite, but in the other species where the tongue is softer it may be pretty acute.

Their skin is naked or covered with scales. The tortoises are remarkable for being covered with a kind of buckler.

Some species of oviparous quadrupeds have six toes. Serpents exercise the sense of touch by wrapping their body round the object which they desire to feel.

The brain of reptiles is very small, and divided into very distinct tubercles. Their sensation seems less to depend on a common centre than in the other animals which we have been considering, as they can live for a long time without the head, and after being deprived of the heart and all the viscera; their limbs when separated from the body preserve their irritability for a considerable time; the heart of a frog will beat for many hours after it has been cut out. Reptiles have also a considerable power of reproduction. The tail of a lizard and several parts of water salamanders will grow again after being cut off. The jaws in these animals are for the most part armed with teeth which are conical and pointed, but some of them have only fleshy or horny gums. Their alimentary canal is but small, and has no cæcum, but it receives fluids similar to those of the hot-blooded animals. The urine, which is secreted by the kidneys, is received into a bladder, but is evacuated by the anus.

Their heart has only one ventricle, from which proceeds a single artery divided into two large branches, which furnish each a twig to the lung of that side, and are then united to be distributed to the other parts of the body. Hence these animals can at pleasure suspend respiration without stopping the circulation of the blood, so that they can remain a long time under water, or in a close vessel. The cells of the lungs are much larger than in the hot-blooded animals; and these organs resemble oblong bags, which float in the same cavity with the other viscera, without the interposition of a diaphragm. Some of these animals have the power of inflating their lungs to a great extent. They have a windpipe and a larynx, by which they can produce sounds as in other animals which are provided with nerves.

The females of reptiles have a double receptacle for eggs, furnished with two tubes, which open at the anus. In some species copulation takes place, and the eggs are covered with a shell more or less hard.

In others the male merely sprinkles with semen the eggs already laid, and these are merely covered with a membrane. Reptiles, no more than other animals with cold blood, have the power of hatching their eggs.

Sect. II. Tortoise.

The covering of this animal is composed of a shell so remarkably hard and firm in its texture, that a loaded waggon may go over it without hurting the shell or the animal within it. In the young animal, this shell grows harder in proportion as its contents expand; and this creature never changes its shell as some others do; hence it was necessary for it to be made up of different pieces; and these are more or less distinct in different animals. Their feet are small and weak; and they are exceedingly slow in motion.

It has neither tongue nor teeth; to make up for which, their lips are so hard as to be able to break almost the hardest bodies.

The alimentary canal very much resembles that of the former class.

The principal difference is in the circulation of the blood. The heart has two distinct auricles, without any communication; and under these there is the appearance of two ventricles similar in shape to those of the former class; but they may be considered as one cavity; for the ventricle sends out not only the pulmonary artery, but likewise the aorta; for there is a passage in the septum, by which the ventricles communicate freely, and the blood passes from the left into the right one. From the aorta, the blood returns into the right auricle, while that from the pulmonary artery returns to the left auricle, from which it is sent to the left auricle, &c., so that only a part of the blood is sent to the lungs, the rest going immediately into the aorta; hence the animal is not under the necessity of breathing so often as otherwise it would be.

From the base of the right ventricle goes out the Blood-vessel pulmonary artery and aorta. The pulmonary artery is spent upon the lungs. The aorta may be said to be three in number; for the aorta sinistra ascends through the pericardium in company with the pulmonary artery; and afterwards turns down, and sends off a considerable branch, which splits into two; one of which joins the right aorta, while the other is distributed upon the liver, stomach, intestines, &c. What remains of this aorta runs to the kidneys or posterior extremities of that side. An aorta descendens, &c., after piercing the pericardium, runs down and communicates with the branch already mentioned, is distributed upon the right kidney and inferior extremity, and also upon the bladder and parts of generation. An aorta ascendens, after getting out of the pericardium, supplies the fore-legs, neck, and head. The blood in the superior part of the body returns to the right auricle by two jugular veins, which unite after perforating the pericardium. From the inferior part it returns to the same auricle by two large veins; one on the right side receives the blood in the right lobe of the liver; the other on the left side receives the blood in the left lobe, and also a trunk which corresponds Of fishes corresponds with the inferior vena cava in other animals. The pulmonary vessels run in the left auricle in the common way.

The absorbent system in the turtle, like that in the former class, consists of lacteals and lymphatics, with their common trunks the thoracic ducts; but differs from it in having no obvious lymphatic glands on any part of its body, nor plexus formed at the termination in the red veins.

The lacteals accompany the blood-vessels upon the mesentery, and form frequent net-works across these vessels: near the root of the mesentery a plexus is formed, which communicates with the lymphatics coming from the kidneys and parts near the anus. At the root of the mesentery on the left side of the spine, the lymphatics of the spleen join the lacteals; and immediately above this a plexus is formed, which lies upon the right aorta. From this plexus a large branch arises, which passes behind the right aorta to the left side, and gets before the left aorta, where it assists in forming a very large receptaculum, which lies upon that artery.

From this receptaculum arise the thoracic ducts. From its right side goes one trunk, which is joined by that large branch that came from the plexus to the left side of the right aorta, and then passes over the spine. This trunk is the thoracic duct of the right side; for, having got to the right side of the spine, it runs upwards on the inside of the right aorta, towards the right subclavian vein; and when it has advanced a little above the lungs, it divides into branches, which near the same place are joined by a large branch that comes up on the outside of the aorta. From this part upwards, those vessels divide and subdivide, and are afterwards joined by the lymphatics of the neck, which likewise form branches before they join those from below. So that between the thoracic duct and the lymphatics of the same side of the neck, a very intricate net-work is formed; from which a branch goes into the angle between the jugular vein and the lower part or trunk of the subclavian. This branch lies therefore on the inside of the jugular vein, whilst another gets to the outside of it, and seems to terminate in it, a little above the angle, between that vein and the subclavian.

Into the above-mentioned receptaculum, the lymphatics of the stomach and duodenum likewise enter. Those of the duodenum run by the side of the pancreas, and probably receive its lymphatics and a part of those of the liver. The lymphatics of the stomach and duodenum have very numerous anastomoses, and form a beautiful net-work on the artery which they accompany. From this receptaculum likewise (besides the trunk already mentioned, which goes to the right side) arise two other trunks pretty equal in size; one of which runs upon the left side, and the other upon the right side of the left aorta, till they come within two or three inches of the left subclavian vein; where they join behind the aorta, and form a number of branches which are afterwards joined by the lymphatics of the left side of the neck; so that here a plexus is formed as upon the right side. From this plexus a branch issues, which opens into the angle between the jugular and subclavian vein.

Sect. III. Serpent and Crocodile.

The circulation in these is similar to that of the circulating turtle; but we find only one ventricle. The blood in serpents goes from the right auricle to the ventricle which sends out the pulmonary artery and aorta; the blood from the pulmonary artery returns to the left auricle, that from the aorta going to the right auricle, and both the auricles opening into the ventricle.

Sect. IV. Frog and Lizard.

These differ from the former animals, in having only one auricle and a ventricle; and besides, the ventricle sends out a single artery, which afterwards splits into two parts; one to supply the lungs, the other runs to all the rest of the body; from the lungs and from the other parts, the blood returns into the auricle.

CHAP. VII. ANATOMY OF FISHES.

OF these we may first observe, that they have a very strong thick cuticle, covered with a great number of scales, laid one on another like the tiles of houses. This among other arguments is supposed to prove the human epidermis to be of a squamous structure; but the scales resemble the hairs, wool, feathers, &c. of the creatures that live in air; and below these we observe their proper cuticula and cutis.

The generality of fishes, particularly those shaped like the cod, haddock, &c. have a line running on each side. These lines open externally by a number of ducts, which throw out a mucous or slimy substance that keeps them soft and clammy, and seems to serve the same purpose with the mucous glands or ducts which are placed within many of our internal organs.

In the next place, these creatures have neither atlantal nor sacral extremities, as quadrupeds and fowls; for their progression is performed in a different way. Swimmers from either of those species of animals: for this purpose they are provided with machines, properly consisting of a great number of elastic beams, connected to use of one another by firm membranes, and with a tail of the same texture; their spine is very moveable towards the tail, air-posterior part, and the strongest muscles of their bodies bags, &c. are inserted there. Their tails are so framed as to contract to a narrow space when drawn together to either side, and to expand again when drawn to a straight line with their bodies; so, by the assistance of this broad tail, and the fins on their sides, they make their progression much in the same way as a boat with oars on its sides and rudder at its stern. The perpendicular fins situated on the superior part of their body keep them in equilibrium, hindering the belly from turning uppermost; which it would readily do, because of the air-bag. Of fishes, air-bag in the abdomen rendering their belly specifically lighter than their back; but by the resistance these fins meet when inclined to either side, they are kept with their backs always uppermost.

It may be next observed, that these creatures have nothing that can be called a neck, seeing they seek their food in a horizontal way, and can move their bodies either upwards or downwards, as they have occasion, by the contraction or dilatation of the air-bag; a long neck, as it would hinder their progression, would be very disadvantageous in the element they live in.

In the bony fishes the bodies of the vertebrae are sometimes cylindrical, sometimes angular, and frequently compressed: they are articulated only by their bodies, as there are no articulatory processes. They may be divided into two classes: those of the tail, which are furnished with a spinous process both above and below; and those of the belly or back, which have it only above. These last are usually furnished, at

the sides, with transverse processes for the attachment of fish of the ribs. The spinous processes, both dorsal and sternal, are very long, especially in flat fish. At the base of the dorsal processes there is a canal for lodging the spinal marrow; and the blood vessels pass through a similar canal at the base of the sternoid processes. There is nearly the same structure in the cartilaginous fishes; but in these all the cartilages are so firmly fixed together, that only the spinous processes can be distinguished. The vertebra of a fish differs from that of other animals in the structure of its body, at each extremity of which there is a conical cavity, so that between each pair of vertebrae there is a hollow space formed by these two cones joined base to base, filled with a very soft cartilaginous or mucous substance on which the motions of the vertebrae are easily performed. The annexed table shows the proportional number of vertebrae of several species of fish.

### TABLE of the Number of Vertebrae in several species of Fishes.

| Species | Cervical Vertebrae | Dorsal Vertebrae | Lumbar Vertebrae | Coccygian Vertebrae | Total No of Vertebrae | |--------------------------|--------------------|------------------|------------------|---------------------|----------------------| | Raia bates. Ray | Ossified into one piece | 4 | 80+ | | | | Squalus. Shark | | | | | 207 | | Accipenser sturio. Sturgeon | | | | | 28 | | Synognathus acus. Sea-needle | | | | | 50+ | | hippocampus. Sea-horse | | | | | 62 | | Balistes | | | | | | | Ostracion quadricornis | | | | | 13 | | Murena anguilla. Eel | | | | | 115 | | Anarrhichas lupus. Sea-wolf | | 2 | 24 | 50 | | | Trachinus draco. Sea-dragon | | 2 | 13 | 30 | | | Uranoscopus. Uranoscope | | 1 | 9 | 15 | | | Gadus merlangus. Whiting | | 2 | 17 | 4 | 32 | 55 | | Cottus scorpius. Sea-scorpion | | 8 | 2 | 15 | | | Trigla loricata. Armed trigla | | 12 | | 23 | | | cuculus. Red gurnard | | 13 | | 21 | | | volitans. Flying trigla | | 3 | 8 | 12 | | | Echineis remora. Remora | | | | | 15 | | Pleuronectes platessa. Plaice | | 13 | | 30 | | | Gasterosteus pungitius. Stickle-back | | 70 | | 22 | | | Perca fluviatilis. Perch | | 21 | | 20 | | | Zeus faber. Dorce | | 4 | 9 | 2 | 16 | 31 | | vomer | | | | | 13 | | Chaetodon cornu. Horned chetodon | | 9 | | 12 | | | teira. Striped chetodon | | 9 | | 12 | | | Cyprinus carpio. Carp | | 1 | 15 | 9 | 16 | 41 | | nasus | | 1 | 19 | 5 | 19 | 44 | | Clupea harengus. Herring | | 4 | 38 | | 18 | | Salmo rhombus. Rhomboid salmon | | 1 | 12 | | 20 | | Esox lucius. Pike | | 4 | 35 | | 20 | | brasiliensis. Brasilian pike | | 34 | 3 | 15 | | | Silurus felis. Sea-cat | | 1 | 12 | 1 | 30 | 44 | | Loricaria. Armour-fish | | 1 | 6 | 1 | 28 | 36 | | Fistularia tabaccaria. Tobacco-pipe fish | | 59 | | 22 | | The brain in fishes is formed pretty much in the same way as that of fowls; only we may observe, that the posterior lobes bear a greater proportion to the anterior.

The organ of smelling is large; and they have a power of contracting and dilating the entry into their nose as they have occasion. It seems to be mostly by their acute smell that they discover their food; for their tongue seems not to have been designed for a very nice sensation, being of a pretty firm cartilaginous substance; and common experience evinces, that their sight is not of so much use to them as their smell in searching for their nourishment. If you throw a fresh worm into the water, a fish will distinguish it at a considerable distance; and that this is not done by the eye, is plain from observing, that after the same worm has been a considerable time in the water, and lost its smell, no fishes will come near it; but if you take out the bait, and make several little incisions into it, so as to let out more of the odoriferous effluvia, it will have the same effect as formerly. Now it is certain, that had the creatures discovered this bait with their eyes, they would have come equally to it in both cases. In consequence of their smell being the principal means which they have of discovering their food, we may frequently observe their allowing themselves to be carried down with the stream, that they may ascend again leisurely against the current of the water; thus the odoriferous particles swimming in that medium, being applied more forcibly to their smelling organs, produce a stronger sensation.

The optic nerves in these animals are not confounded with one another in their middle progress betwixt their origin and the orbit, but the one passes over the other without any communication; so that the nerve that comes from the left side of the brain goes distinctly to the right eye, and vice versa.

Indeed it would seem not to be necessary for the optic nerves of fishes to have the same kind of connection with each other as those of man have; for their eyes are not placed in the fore part, but in the sides of their heads; and of consequence, they cannot so conveniently look at any object with both eyes at the same time.

The crystalline lens is here a complete sphere, and more dense than in terrestrial animals, that the rays of light coming from water might be sufficiently refracted.

As fishes are continually exposed to injuries in the uncertain element in which they live, and as they are in perpetual danger of becoming a prey to the larger ones, it was necessary that their eyes should never be shut; and as the cornea is sufficiently washed by the element they live in, they are not provided with palpebrae; but then, as in the current itself the eye must be exposed to several injuries, there was a necessity it should be sufficiently defended; which in effect it is by a firm pellucid membrane, that seems to be a continuation of the cuticula, being stretched over here. The epidermis is so very proper for this purpose, as being insensible and destitute of vessels, and consequently not liable to obstructions, or, by that means, of becoming opaque. In the eye of the skate tribe, there is a digitated curtain which hangs over the pupil, and may shut out the light when the animal rests; and it is similar to the tunica adnata of other animals.

Although it was formerly much doubted whether fishes possessed a sense of hearing, yet there can be little doubt of it now; since it is found that they have a complete organ of hearing as well as other animals, and likewise as the water in which they live is proved to be a good medium. Fishes, particularly those of the skate kind, have a bag at some distance behind the eyes, which contains a fluid and a soft cretaceous substance, and supplies the place of vestibule and cochlea. There is a nerve distributed upon it, similar to the portio mollis in man. They have three semicircular canals, which are filled with a fluid, and communicate with the bag; they have likewise, as the present professor of anatomy at Edinburgh has discovered, a meatus externus, which leads to the internal ear. The cod fish, and others of the same shape, have an organ of hearing somewhat similar to the former; but instead of a soft substance contained in the bag, there is a hard cretaceous stone. In this kind of fish no meatus externus has been yet observed; And Dr Monro is inclined to think that they really have not one, from the consideration that the common canal or vestibule, where the three semicircular canals communicate, is separated from the cavity of the cranium by a thin membrane only; that this cavity, in the greater number of fishes, contains a watery liquor in considerable quantity; and that, by the thinness of the cranium, the tremor excited by a sonorous body may readily and easily be transmitted through the cranium to the water within it, and so to the ear.

The belly is covered on the inferior part with a black-coloured thin membrane resembling our peritoneum. It is divided from the chest by a thin membranous partition, which has no muscular appearance; so that we have now seen two different sorts of animals that have no muscular diaphragm.

These creatures are not provided with teeth proper for breaking their aliment into small morsels, as the what food they use is generally small fishes, or other animals that need no trituration in the mouth, but spontaneously and gradually dissolve into a liquid chyle. Their teeth serve to grasp their prey, and hinder the creatures they have once caught from escaping again. For the same purpose, the internal cartilaginous basis of the bronchi, and the two round bodies situated in the posterior part of the jaws, have a great number of tentacles fixed into them, in such a manner as that any thing can easily get down, but is hindered from getting back. The water that is necessarily taken in along with their food in too great quantities to be received into their jaws in deglutition, passes betwixt the interstices of the bronchi and the flap that covers them. The compression of the water on the bronchi is of considerable use to the creature, as we shall explain by and by.

The gullet in these creatures is very short, and digestion scarcely distinguished from their stomach, seeing their performed food lies almost equally in both. The stomach is of solely by an oblong figure. There are commonly found small menstruum fishes in the stomach of large ones still retaining their natural form; but when touched, they melt down into These creatures have a membranous diaphragm, which forms a sac in which the heart is contained. It is very tense, and almost perpendicular to the vertebral.

The branchiae lie in two large slits at each side of their heads, and seems to be all they have that bears close analogy to lungs. Their form is semicircular; structure they have a vast number of red fibrilse standing out on each side of them like a fringe, and very much resemble the vane of a feather. These branchiae are perpetually subjected to an alternate motion and pressure from the water; and we may here remark, that we have not found any red blood but in places subjected to this alternate pressure. This observation will help us in explaining the action of the lungs upon the blood. Over these gills there is a large flap, allowing a communication externally; by which the water they are obliged to take into their mouths with their food finds an exit without passing into their stomach; it is owing to these flaps coming so far down that the heart is said commonly to be situated in their heads. The blood is collected again from the gills by a vast number of small veins, somewhat in the same manner as our pulmonary vein; but instead of going back to the heart a second time, they immediately unite, and form an aorta descendens, without the intervention of an auricle and ventricle. Hence a young anatomist may be puzzled to find out the power by which the blood is propelled from the gills to the different parts of the body; but the difficulty will be considerably lessened when we consider the manner in which the blood is carried through the liver from the intestines in man and quadrupeds. The aorta in fishes sends off branches which supply all the parts of the body excepting the gills. From the extremity of those branches the blood returns to the heart somewhat in the same manner as in the former class of animals; only there are two inferior venae cavae, whereas the former has but one.

Absorbent System in Fishes. We shall take the haddock as a general example; for the other fishes, particularly those of the same shape, will be found in general to agree with it.

On the middle of the belly of a haddock, immediately below the outer skin, a lymphatic vessel runs up-wards from the anus, and receives branches from the parietes of the belly, and from the fin below the anus; near the head this lymphatic passes between the two pectoral fins; and having got above them, it receives their lymphatics. It then goes under the symphyses of the two bones which form the thorax, where it opens into a net-work of very large lymphatics, which lie close to the pericardium, and almost entirely surrounds the heart. This net-work, besides that part of it behind the heart, has a large lymphatic on each side, which receives lymphatics from the kidney, runs upon the bone of the thorax backwards; and when it has got as far as the middle of that bone, it sends off a large branch from its inside to join the thoracic duct. After detaching this branch, it is joined by the lymphatics of the thoracic fins, and soon after by a lymphatic which runs upon the side of the fish. It is formed of branches, which give it a beautiful penniform appearance.

Besides these branches, there is another set deeper which which accompanies the ribs. After the large lymphatic has been joined by the above mentioned vessels, it receives lymphatics from the gills, orbit, nose, and mouth. A little below the orbit, another net-work appears, consisting in part of the vessels above described, and of the thoracic duct. This net-work is very complete, some of its vessels lie on each side of the muscles of the gills; and from its internal part a trunk is sent out, which terminates in the jugular vein.

The lacteals run on each side of the mesenteric arteries, anastomosing frequently across these vessels. The receptaculum into which they enter is very large, in proportion to them; and consists at its lower part of two branches, of which one lies between the duodenum and stomach, and runs a little way upon the pancreas, receiving the lymphatics of the liver, pancreas, those of the lower part of the stomach, and the lacteals from the greatest part of the small intestines. The other branch of the receptaculum receives the lymphatics from the rest of the alimentary canal. The receptaculum formed by these two branches lies on the right side of the upper part of the stomach, and is joined by some lymphatics in that part, and also by some from the sound and gall-bladder, which in this fish adheres to the receptaculum. This thoracic duct takes its rise from the receptaculum, and lies on the right side of the oesophagus, receiving lymphatics from that part; and running up about half an inch, it divides into two ducts, one of which passes over the oesophagus to the left side, and the other goes straight upon the right side, passes by the upper part of the kidney, from which it receives some small branches, and soon afterwards is joined by a branch from the large lymphatic that lies above the bone of the thorax, as formerly mentioned: near this part it likewise sends off a branch to join the duct of the opposite side; and then, a little higher, is joined by those large lymphatics from the upper part of the gills, and from the fauces.

The thoracic duct, after being joined by these vessels, communicates with the net-work near the orbit, where its lymph is mixed with that of the lymphatics from the posterior part of the gills, and from the superior fins, belly, &c., and then from this net-work a vessel goes into the jugular vein just below the orbit. This last vessel, which may be called the termination of the whole system, is very small in proportion to the net-work from which it rises; and indeed the lymphatics of the part are so large, as to exceed by far the size of the sanguiferous vessels.

The thoracic duct from the left side, having passed under the gullet from the right, runs on the inside of the vena cava of the left side, receives a branch from its fellow of the opposite side, and joins the large lymphatics which lie on the left side of the pericardium, and a part of those which lie behind the heart; and afterwards makes, together with the lymphatics from the gills, upper fins, and side of the fish, a net-work, from which a vessel passes into the jugular vein of this side. In a word, the lymphatics of the left side agree exactly with those of the right side above described. Another part of the system is deeper seated, lying between the roots of the spinal processes of the backbone. This part consists of a large trunk that begins from the lower part of the fish, and as it ascends receives branches from the dorsal fins and adjacent parts of the body. It goes up near the head, and sends a branch to each thoracic duct near its origin.

The only organs of generation in this animal are two bags situated in the abdomen uniting near the podex. These in the male are filled with a whitish firm substance called the milk, and in the female with an infinite number of little ova clustered together, of a reddish yellow colour, called the roe. Both these at spawning time we find very much distended; whereas at another time the male organs can scarcely be distinguished from the female; nor is there any proper instrument in the male for throwing the seed into the organs of the female, as in other creatures. We shall not take upon us to determine the way whereby the female sperm is impregnated; but we find that the spawn of frogs consists in the small specks wrapped up in a whitish glutinous liquor: these specks are the rudiments of the young frogs, which are nourished in that liquor till they are able to go in search of their food. In the same way, the ova of fishes are thrown out and deposited in the sand, the male being for the most part ready to impregnate them, and they are incubated by the heat of the sun. It is curious enough to remark with what care they seek for a proper place to deposit their ova, by swimming to the shallow, where they can better enjoy the sun's rays, and shun the large jaws of other fishes. The river-fishes, again, spawn in some creek free from the hazard of the impetuous stream. But whether this mixture be brought about in fishes by a simple application of the genitals to each other, or if both of them throw out their liquors at the same time in one place, and thus bring about the desired mixture, it is not easy to determine. Spallanzani has found, that the eggs of frogs, toads, and water newts, are not fecundated in the body of the female; that the male emits his semen upon the spawn while it is flowing from the female; and that the fetus pre-exists in the body of the female: but whether impregnation takes place in the same manner in fishes, he has not yet been able to determine, though he seems to think it probable. These creatures are so shy, that we cannot easily get to observe their way of copulation, and are consequently but little acquainted with their natural history. Frogs, it is very evident, do not copulate: at least no farther than to allow both sexes an opportunity of throwing their sperm. Early in the spring the male is found for some days in close contact upon the back of the female, with his fore legs round her body in such a manner that makes it very difficult to separate them, but there is no communication. At this time the female lays her spawn in some place that is most secure, while the male emits his sperm upon the female spawn.

After raising up the black peritoneum in fishes, there The air comes in view an oblong white membranous bag, in bladder, which there is nothing contained but a quantity of elastic air. This is the swimming-bladder: it lies close to the back-bone; and has a pretty strong muscular coat, whereby it can contract itself. By contracting this bag, and condensing the air within it, they can make their bodies specifically heavier than water, and so readily fall to the bottom; whereas the muscular fibres ceasing to act, the air is again dilated, and they become specifically lighter than water, and so swim above. According to the different degrees of contraction and dilatation of this bladder, they can keep higher or lower in the water at pleasure. Hence flounders, soles, raia or skate, and such other fishes as want this sac, are found always grovelling at the bottom of the water: it is owing to this that dead fishes (unless this membrane has been previously broken) are found swimming a-top, the muscular fibres then ceasing to act, and that with their bellies uppermost; for the backbone cannot yield, and the distended sac is protruded into the abdomen, and the back is consequently heaviest at its upper part, according to their posture.

There is here placed a glandular substance, containing a good quantity of red blood; and it is very probable that the air contained in the swimming-bladder is derived from this substance. From the anterior part of the bag go out two processes or appendices, which, according to the gentlemen of the French academy, terminate in their fauces; in a variety of other fishes we find communications with some part of the alimentary canal, particularly the oesophagus and stomach. The salmon has an opening from the fore end of the air-bag into the oesophagus, which is surrounded by a kind of muscular fibres. The herring has a funnel-like passage leading from the bottom of the stomach into the air-bag; but it is not determined whether the air enters the air-bag by this opening, or comes out by it: the latter, however, seems to be the more probable opinion, as the glandular body is found in all fishes, whereas there are several without this passage of communication.

At the superior part of this bag there are other red-coloured bodies of a glandular nature, which are connected with the kidneys. From them the ureters go down to their insertion in the vesica urinaria, which lies in the lower part of the abdomen; and the urethra is there produced, which terminates in the podex.

CHAP. VIII. OF MOLLUSCA.

In these animals the muscles or fleshy fibres are white, and possessed of great irritability: they retain the power of motion even after being cut into small pieces; and many parts of their body are capable of being reproduced after being separated. Their external surface is always moist, as there commonly exudes from it a viscous fluid. It is extremely sensible, and is furnished with organs called tentaculae, which are capable of being lengthened out or contracted, so as to enable the animal to feel the better. It is uncertain whether or not these animals possess the sensation of smell, but if they do, the organ of this sense is probably situated at the entrance of their pulmonary vessels. Many of them have eyes, and some appear to be possessed of ears.

Their body is usually provided with, or at least partly enveloped by, a membranous covering. In many this covering is more or less crustaceous, produced from a calcareous juice exuding from the surface of the animal, and forming a shell composed of one or more pieces or valves. The body of the animal is attached to this shell by muscles, which enable it to retire within the valves, or to shut these together. These muscles change their place, separating from one part, and growing to another, so as always to preserve the same relative position, notwithstanding the unequal growth of the shell. Most of these animals are inhabitants of the sea; some of them reside in fresh water; and some of them reside entirely on land.

The mollusca may be divided into three orders.

1. The cephalopoda, so called because their feet, or at least the organs with which they seize their prey, are situated in the head. Their body is in the form of a sack, which, when the external covering is removed, exhibits the appearance of a compact network of fleshy fibres in three distinct layers. Of these the outermost are placed lengthwise, the middle in a cross direction, and the innermost in no regular order. By the various actions of these fibres the sack of the animal is lengthened, contracted, bent, or twisted in various directions.

These animals are furnished below the skin of the back with a solid body, which is for the most part exceedingly elastic and transparent, and is sometimes furrowed longitudinally. In all the species of sepia or cuttle-fish, except the S. octopus, which wants it, this body is a sort of bone, formed of thin concentric plates, separated by small columns, arranged so as to form a quincunx. It is oval and lenticular, or thickest in the middle.

The feet in this order are eight in number, and form a circle round the mouth; they end in suckers, by which the animal fixes itself to any substance, and are furnished with numerous muscles, by which they are moved in every direction. The other species of sepia (except the octopus and the calmar), have, besides these eight feet, two others which are longer and smaller.

They have three hearts; their respiration is carried on in the water by means of branchiae; they have very large eyes, and organs of hearing situated within the head; their stomach is very fleshy, so as to resemble the gizzard of a fowl, and they have a very large liver. They are also furnished with a peculiar gland for the purpose of secreting an inky fluid, which, when they wish to conceal themselves, they throw out, and thus obscure the water round them.

2. The gastropoda, which have upon the belly a muscular plane, by the contraction of which they creep upon the belly, as may be observed in the snail; and hence their name. They have no heart; their branchiae are situated sometimes within the body, sometimes they surround the body, and are often on the back: they are naked in the first case, and in the others are covered with a kind of lid, and are of various forms. The common trunk of the blood-vessels is subdivided for the purpose of distributing to the branchiae the blood which has circulated through the body. The most of this order are hermaphrodite, but require reciprocal copulation. There is almost always situated near the matrix a bag, containing a fluid, which CHAP. IX. OF THE CRUSTACEA.

THE animals which compose this order have commonly been ranked among the insects; but we have thought it better to separate them, as they are possessed of character by which they are sufficiently distinguished. They have the body enveloped in a sort of armour composed of several pieces or scales, and are usually provided with a great number of jointed limbs.

The head in these animals is immoveable, their principal motions being confined to the tail and feet. The tail forms a considerable portion of the animal, and is furnished with very large and strong muscles, by the action of which the animal is enabled to leap and swim with great celerity.

Their feet are of different forms in the several species, and also vary in number, and in some species answer several very different purposes. What in these animals is analogous to the brain, is a long knotted nervous cord, from the knots of which the nerves are distributed to the body. Their eyes are hard and complex, and are usually placed on a sort of footstalks, which enable them to move with great facility in all directions. They are furnished with feelers and antennae, as we shall see in insects. Their organs of hearing are very imperfect. They have a heart, and both an arterial and a venous system of blood-vessels. They breathe by means of branchiae. Their jaws are generally numerous, very strong, and situated in a transverse direction. They are of distinct sexes, and the male has two pences.

CHAP. X. OF INSECTS.

AS under Entomology, now become a study so fashionable, and which has been carried to a high degree of perfection, we propose to give a particular account of the structure and economy of insects, we shall at present only offer a short sketch of their anatomy.

Insects differ from the former classes, by their bodies being covered with a hard crust or scale, by their having feelers or antennae arising from their head, and many of them breathing the air through lateral pores. As to the shape of their bodies, though it somewhat differs from that of birds, being in general not so sharp before to cut and make way through the air, yet it is well adapted to their manner of life. The base of their bodies is not formed of bones, as in many other animals, but the hard external covering serves them for skin and bone at the same time. Their feelers, beside the use of cleaning their eyes, are a guard to them in their walk or flight. Their legs and wings are well fitted for their internal surface; but the latter vary so much in different insects, that from them naturalists have given names to the several orders of the class. As, first, the Coleoptera, or beetle tribe, which have a crustaceous elytra or shell, that shuts together, and forms a longitudinal suture down their back.

Hemiptera—as in cimex, cockroach, bug, &c., which have the upper wings half crustaceous and half membranaceous; not divided by a longitudinal suture, but incumbent on each other.

Lepidoptera—as the butterfly, have four wings, covered with fine scales in the form of powder.

Neuroptera—as the dragon-fly, spring-fly, &c., have four membranaceous transparent naked wings, generally reticulated.

Hymenoptera—as wasps, bees, &c., have four membranaceous wings, and a tail furnished with a sting.

Diptera—as the common house-fly, have only two wings.

Aptera—as the scorpion, spider, &c., have no wings.

The structure of the eye in many insects is a most curious piece of mechanism. The outer part is remarkably hard, to guard against injuries; and has commonly a reticular appearance, or the whole may be looked upon as an assemblage of smaller eyes; but whether they see objects multiplied before them, has not yet been determined.

Linnaeus, Linnaeus, and several others following him, deny the existence of a brain in these creatures.

Their ear has been lately discovered to be placed at the root of their antennae or feelers, and can be distinctly seen in some of the larger kinds.

They have a stomach, and other organs of digestion. They have a heart and blood vessels, and circulation is carried on in them somewhat as in the former class; but the blood is without red globules; or, as naturalists speak, is colourless. In some of the larger kind, when a piece of the shell is broken, the pulsation of the heart is seen distinctly, and that sometimes for several hours after it has been laid bare.

Lungs. The existence of these by some has been denied. But late experiments and observations show that no species want them, or at least something similar to them; and in many insects, they are larger in proportion than in other animals: in most of them they lie on or near the surface of their body; and send out lateral pores or tracheæ, by which, if the animal is besmeared with oil, it is instantly suffocated.

Generation. The same difference in sex exists in insects as in other animals, and they even appear more disposed to increase their species; many of them, when become perfect, seeming to be created for no other purpose but to propagate their like. Thus the silk-worm, when it arrives at its perfect or moth state, is incapable of eating, and can hardly fly; it endeavours only to propagate its species: after which the male immediately dies, and so does the female as soon as she has deposited her eggs.

Besides those of the male and female, a third sex of Worms exists in some insects, which we call neuter. As these have not the distinguishing parts of either sex, they may be considered as eunuchs or infertile. We know of no instance of this kind in any other class of animals; and it is only found among those insects which form themselves into societies, as bees, wasps, and ants: and here these eunuchs are real slaves, as on them lies the whole business of the economy. No hermaphrodites have as yet been discovered among insects.

Many have imagined that the generality of insects were merely the production of putrefaction, because they have been observed to arise from putrid substances; but a contrary opinion is now more generally adopted; and it is pretty certain, that if putrid bodies be shut up in a close vessel, no insects are ever generated unless their ova have been originally deposited there. They are oviparous animals, and lay their eggs in places most convenient for the nourishment of their young; some in water, others in flesh; some in fruit and leaves; while others make nests in the earth or in wood, and sometimes even in the hardest stone. The eggs of all insects first become (larva) caterpillar, or maggot; from which they are changed into (pupa) chrysalis or aurelia, so named from their being inclosed in a case; and these dying, or seeming to die, the (imagæ) fly, or butterfly, or perfect state, succeeds; and during each of these changes their appearance differs wonderfully.

CHAP. XI. OF WORMS.

The worms form a class in the system of Linnaeus, comprehending the mollusca, and the next assemblage of which we are to speak, viz. the Zoophytes, besides the worms properly so called.

We have seen that insects in one part of their existence appear in the state of larvæ, or organized beings resembling the common caterpillar or larva of the butterfly. In some of these the organs of motion are very perfect, and they are furnished with regular articulated members, provided with solid parts. From these there is a gradation to the worms, which have no feet, but move forwards either by means of bristles or hairs fixed in the surface of their bodies, as in the common earth-worm and the lumbricus of the intestines, or they are provided at each extremity with a circular sucker, as in the leech, by which they fasten one end of their body to the surface on which they are to move, and proceed forward by the contractions of the muscular rings of which their body is chiefly composed. Within their body is found a white nervous cord. Those which inhabit the water carry on respiration by means of membranaceous branchiae; in others there are pores or stigmata, analogous to the tracheæ of insects; some of them are furnished with feelers. Of the most important of this class, the worms which inhabit the intestines of other animals, we propose to give a particular account in a future article.

CHAP. XII. OF THE ZOO PHYTES.

The zoophytes form the lowest class of animated nature; and many of them bear so close a resemblance to plants and minerals, that they would seem to belong rather to these kingdoms than to that in which modern naturalists have agreed to arrange them. The mollusca possess organs of digestion, sensation, circulation, and respiration, and are furnished with viscera not very unlike those of the vertebral animals. Insects form the next degree, which have no distinct circulation, and very imperfect respiratory organs; but in them we see something like a brain, and well-marked organs of sensation. We observe the same in many worms, in most of which they probably exist. But in the zoophytes there is no appearance of circulation; there are no nerves, and no sensorium or common centre of sensation; there is but little appearance ### INDEX

**A**

**ABDOMEN**, use of the vesicles in, 272 Air-bladder in fishes, 305 Allantois in cows, arguments for and against the human, 245 Amnios in cows, 246 Amygdals, 181 Anatomy, Comparative, many advantages from the study of, helps to explain ancient writers, diversities of organization in, considered, 148 Angiology, Animal motion, the simplest function of, differences in the sensitive organs of an, 151 Aorta ascendens in dogs, ascendens and descendens in a cow, 236 Appendix vermiformis, 193 Arm, bones of the, right, mechanical account of the superior strength of, 205 Astragalus, 65

**B**

Beaks, the variety in those of fowls, 255 Bile, 98 Birds, anatomy of, wings, how furnished, wings of, why not placed in the middle of the body, covering of, carnivorous, Bladder, in dogs, connexion of the, why the human only partly covered by the peritoneum, a stimulus a principal cause of the evacuation of the, in cows, 217

**Blood**, circulation of, nature of, vessels of, in tortoises, Bone, occipital, Bones, composition of, connexion of, marrow, parietal, temporal, Bourse noire in birds, Brain, integuments of, parts of, Branchiae, Breasts, Bursae mucosae, structure of, compared with the capsular ligaments of the joints,

**C**

Capsula atrabiliaris, Corpus, Cartilages, Cellular membrane, Cerebrum, Cerebellum, in fishes, Chest, Chorion in cows, Circulation, important distinctions in the organs of, Clavícula, Coitus, Colon, Conception, Cor in birds, Cornua uteri in cows, Cotyloides in cows, Cow, history of, as a ruminant animal, has four stomachs, names of the stomachs, Cranium, bones of, Crop in birds, Crustacea, p. 312 Crystalline humour in fishes a complete sphere,

**D**

Deglutition, Defecation, Diaphragm, in dogs, in birds, in fishes, Digestion, organs of, furnish us with two great distinctions, action of the organs of, forms the chyle, power of the organs of, in fishes performed wholly by a menstruum, Dog, anatomy of, brain of, Ductus choledochus in birds, Duodenum, in a cow, in birds, Epidermis, how it invests the internal surface of all the cavities and vessels of the human body, Epiglottis, Eye in birds, Extremities, upper, lower, Face, bones of the, Fetus in utero, Fat, Fibula, Fingers, Fishes, anatomy of, cuticula similar to the human, uses of the fins, tail, air-bags, &c. of, teeth of, heart of, has but one auricle and one ventricle, Foot, | Index | Anatomy | |-------|---------| | N° 63 | Lymphatics in fishes, | | | in tortoises, | | | M | | 249 | Mamme, | | 285 | Man, whether a biped or a quadruped, | | 107 | Mastication, | | 157 | Maxilla inferior, | | 201 | Mediasinum, | | 137 | Medulla oblongata, | | 174 | Membrana nictitans, | | 94 | Mesentery, | | 196 | in dogs, | | 55 | Metacarpus, | | 70 | Metatarsus, | | 311 | Mollusca, | | 105 | Mouth, form and position of the, | | 85 | Muscles, | | 175 | Musculus suspensorius, | | 81 | N | | 144 | Nails, | | 254 | Nates and testes in dogs, | | 292 | Neck, vertebrae of the, | | 125 | of a dog, | | 139 | Nerves, | | 172 | Nose of a dog, | | 130 | Nutrition, | | 92 | Oesophagus, | | 96 | Omentum, | | 187 | in dogs, | | 290 | Optic nerve in fishes, | | 157 | Organization and functions, variations which take place among, | | 158 | instance of, | | 110 | Organs, male, of generation, | | 111 | female, of generation, | | 12 | Os frontis, | | 16 | sphenoides, | | 28 | ethmoides, | | 34 | hyoides, | | 35 | sacrum, | | 40 | coccyx, | | 41 | ilium, | | 42 | ischium, | | 49 | pubis, | | 53 | humeri, | | 66 | femoris, | | 67 | calcis, | | 68 | navicular, | | 19 | cuboides, | | 20 | Osse malarum, | | 21 | maxillaria superiora, | | 22 | naso, | | 23 | unguis, | | 25 | palati, | | 26 | spongiosa inferiora, | | 69 | cuneiformia, | | 72 | sesamoides, | | 95 | Pancreas, | | 97 | asellis in dogs, | | 266 | in birds, | | 296 | in fishes, | | 37 | Panniculus carnosus, whence the motion of, | | 210 | Papilla, | | 39 | Pelvis, bones of the, | | 211 | in quadrupeds, | | 223 | Penis, | | 124 | Pericardium, | | 4 | Periosteum, | | 89 | Peritoneum, | | 78 | Perspiration, insensible, and sweat, | | 80 | dispute whether these are one and the same or different excretions, | | 79 | uses of, | | 116 | Pleura, | | 168 | Processus mamillaris, | | 225 | Prostata, | | 271 | Pulmones in birds, | | 176 | Pupilla, | | 163 | Quadrupeds, cuticula, cutis, and panniculus carnosus in, | | 165 | why most want clavicles, | | 167 | falx of, | | 5 | Radius, | | 91 | Rectum in dogs, | | 280 | Reptiles, | | 121 | Respiration, of, | | 155 | organs of, display striking varieties, | | 159 | and motion, relation between, | | 75 | Rete mucosum, | | 170 | mirabile galeni in dogs, | | 38 | Ribs, | | 208 | in dogs, | | 59 | Rotula, | | 47 | Scapula, | | 226 | Scrotum, | | 131 | Secretions, of, | | 160 | Sensation, differences between the organs of, and those of respiration, | | 140 | Senses, | | 151 | differences in the external, | | 285 | Serpents, circulation in, | | 45 | Shoulder, | | 10 | Skeleton, | | 73 | Skin, | | 143 | Smelling, | | 251 | in birds, | | 289 | in fishes, | | 30 | Spine, | | 99 | Spleen, | | 199 | in dogs, | | 233 | in cows, | | 267 | in birds, | | 298 | in fishes, | | 37 | Sternum, | | 207 | in a dog, | | 96 | Stomach, | | 188 | in quadrupeds, | | 287 | Swimming of fishes, how performed, | | 275 | Tapetum, |

| Topic | Page | |-------|------| | Topetum | 177 | | Tarsus | 64 | | Taste, the sense of | 142 | | Teeth, in dogs | 27 | | Testes | 222 | | Thirst, of | 106 | | Thymus | 117 | | Tibia | 61 | | Toes | 71 | | Tongue | 171 | | Tortoise shell and covering of the | 281 | | Touch, sense of | 141 | | Trachea | 119 | | Trunk, bones of the | 29 | | Vasa spermatica | 218 |

| Topic | Page | |-------|------| | Veins, lacteal | 103 | | Vena pendulum palati in dogs | 182 | | Vena cava | 203 | | Ventriculus succenturiatus, seu infundibulum, in birds | 257, 264 | | its communication with the air-bladder | 306 | | Vertebrae of the back | 32 | | lumbar | 33 | | Vesica fells in birds | 269 | | Vesiculae seminales, how the want of them is supplied | 221 | | how supplied in birds | 280 | | Vis insita, nervea | 86 | | Vision | 87 | | Vitellarium in birds | 144 | | Voice | 278 | | differences in the organs of | 121 | | Vomer | 156 | | Ulna | 51 | | Ureters | 102 | | Urine | 213 | | Urinary bladder | 308 | | Uterus in dogs | 103 | | in cows | 226 | | if thicker in time of gestation | 239 | | Uvula, the use of it in man | 141 | | Wind-pipe in birds | 279 | | Worms | 313 | | Zoophytes | 313 |

ANA

Anattom, in Geography, the most southerly island of the New Hebrides, in the southern Pacific ocean. S. Lat. 20° 3', E. Long. 170° 4'.