id not confine his researches to the study of relative anatomy. He investigated the intimate structure of organs with assiduity and success. What was too minute for unassisted vision he inspected by means of glasses. Structure, which could not be understood in the recent state, he unfolded by maceration in different fluids, or rendered more distinct by injection and exsiccation. The facts unfolded in these figures are so important, that it is justly remarked by Lauth, that if the author himself had been fortunate enough to publish them, anatomy would have attained the perfection of the 18th century two centuries earlier at least. Their seclusion for that period in the papal library has given celebrity to many names, which would have been known only in the verification of the discoveries of Eustachius.
Eustachius was the contemporary of Vesalius. Columbus and Fallopius were his pupils. The former, as his immediate successor in Padua, and afterwards as professor at Rome, distinguished himself by rectifying and improving the anatomy of the bones; by giving correct accounts of the shape and cavities of the heart, of the pulmonary artery and aorta, and their valves, and tracing the course of the blood from the right to the left side of the heart; by a good description of the brain and its vessels, and by correct understanding of the internal ear, and the first good account of the ventricles of the larynx.
The latter, who after being professor at Pisa in 1548, and at Padua in 1551, died at the age of 40, studied the general anatomy of the bones; described better than heretofore the internal ear, especially the tympanum and its osseous ring, the two fenestrae, and their communication with the vestibule and cochlea; and gave the first good account of the stylo-mastoid hole and canal, of the ethmoid bone and cells, and of the lacrymal passages. In myology he rectified several mistakes of Vesalius. He made some curious researches into the organs of generation in both sexes, and discovered the utero-peritoneal canal which still bears his name.
Osteology nearly at the same time found an assiduous cultivator in John Philip Ingrassias, a learned Sicilian physician, who, in a skilful commentary on the osteology of Galen, corrected numerous mistakes. He gave the first distinct account of the true configuration of the sphenoid and ethmoid bones, and has the merit of first describing the third bone of the tympanum, called stapes, 1546, though this is also claimed by Eustachius and Fallopius. He appears also to have known the fenestrae, the chorda tympani, the cochlea, the semi-circular canals, and the mastoid cells.
The anatomical descriptions of Vesalius underwent the scrutiny of various inquirers, actuated, some by motives of hostility to the individual, others by the more honourable wish to ascertain if his representations accorded with nature. Of the latter, Fallopius was one; but the most distinguished by the importance and veracity of their researches, as well as the temperate tone of their observations, were Julius Caesar Aranzi, anatomical professor for 32 years in the university of Bologna, and Constantio Varoli, physician to Pope Gregory XIII. To the former we are indebted for the first correct account of the anatomical peculiarities of the fetus, and for being the first to show that the muscles of the eye do not, as was falsely imagined, arise from the dura mater, but from the margin of the optic hole. He also, after considering the anatomical relations of the cavities of the heart, the valves, and the great vessels, corroborates the views of Columbus regarding the course which the blood follows in passing from the right to the left side of the heart. I have already mentioned Alexander Achillini as the reputed and probable discoverer of the inferior recesses of the cerebral cavities; but whether he knew them or not, certain it is that neither his contemporaries nor successors gave any proof that they were acquainted with these regions of the brain. Aranzi is the first anatomist who describes them distinctly, who recognises the objects by which they are distinguished, and who gives them the name by which they are still known (bombiceps, hippocampus); and his account is more minute and perspicuous than that of the authors of the subsequent century. He speaks at large of the choroid plexus, and gives a particular description of the fourth ventricle under the name of cistern of the cerebellum, as a discovery of his own.
Italy, though rich in anatomical talent, has produced probably none greater than Constantio Varoli of Bologna. Though limited in the measure of his existence to the short space of 82 years, he acquired reputation not inferior to that of the most eminent of his contemporaries. He is now known chiefly as the author of an Epistle, inscribed to Hieronymo Mercuriati, on the optic nerves, in which he describes a new method of dissecting the brain, and communicates many interesting particulars relating to the anatomy of the organ. Overlooking the fanciful comparison of the transverse eminence and the prolongations (cervus) of the brain and cerebellum to a bridge over the water of an aqueduct, though he examines the lower surface of the organ with tedious minuteness, he gives evidence that he formed a more accurate and just idea of its configuration than any of the best modern anatomists. He observes the threefold division of the inferior surface or base, defines the limits of the anterior, middle, and posterior eminences, as marked by the compartments of the skull, and justly remarks that the cerebral cavities are capacious, communicate with each other, extending first backward and then forward, near the angle of the pyramidal portion of the temporal bone, and that they are folded on themselves, and finally lost above the middle and inferior eminence of the brain. He appears to have been aware that at this point they communicate with the exterior or convoluted surface. He recognised the impropriety of the term corpus callosum, seems to have known the communication, called afterwards foramen Monroianum, and describes the hippocampus more minutely than had been previously done.
Among the anatomists of the Italian school, as a pupil of Fallopius, Eustachius, and Aldrovandus, is generally enumerated Volcher Coiter of Groningen. He distinguished himself by accurate researches on the cartilages, the bones, and the nerves, recognised the value of morbid anatomy, and made some experiments on living animals to ascertain the action of the heart and the influence of the brain.
The Frutefull and Necessary Briefe Worke of John Halle (1565), and The Englishman's Treasure, by Master Thomas Vicary (1586), both English works published at this time, are tolerable compilations, partly from Berenger, partly from Vesalius, and much tinged by the Galenian and Arabian distinctions.
The celebrity of the anatomical school of Italy was worthily maintained by Hieronymo Fabricio d'Aquapendente, who, in imitation of his master Fallopius, laboured to render anatomical knowledge more precise by repeated dissections, and to illustrate the obscure by researches on the structure of animals in general. In this manner he investigated the formation of the fetus, the structure of the esophagus, stomach, and bowels, and the peculiarities of the eye, the ear, and the larynx. The discovery, however, on which his surest claims to eminence rest, is that of the membranous folds, which he names valves, in the interior of veins. Several of these folds had been observed by Fernel, Sylvius, and Vesalius; and in 1547 Cannani observed those of the vena cava; but no one appears to have offered any rational conjecture on their use, or to have traced them through the venous system at large, until Fabricius in 1574, upon this hypothesis, demonstrated the presence of these valvular folds in all the veins of the extremities.
Fabricius, though succeeded by his pupil Julius Casserius of Piacenza, may be regarded as the last of that illustrious line of anatomical teachers by whom the science was so successfully studied and taught in the universities of Italy. The discoveries which each made, and the errors which their successive labours rectified, tended gradually to give anatomy the character of a useful as well as an accurate science, and to pave the way for a discovery which, though not anatomical, but physiological, is so intimately connected with correct knowledge of the shape and situation of parts, that it exercised the most powerful influence on the future progress of anatomical inquiry. This was the knowledge of the circular motion of the blood,—a fact which, though obscurely conjectured by Aristotle, Mondino, and Berenger, and partially taught by Servetus, Columbus, Casalpinus, and Fabricius, it was nevertheless reserved to William Harvey fully and satisfactorily to demonstrate.
I have already shown that Mondino believed that the blood proceeds from the heart to the lungs, through the vena arterialis or pulmonary artery, and that the aorta conveys the spirit into the blood, through all parts of the body. This doctrine was adopted with little modification by Berenger, who further demonstrated the existence and operation of the tricuspid valves in the right ventricle, and of the sigmoid valves at the beginning of the pulmonary artery and aorta, and that there were only two ventricles separated by a solid impervious septum. These were afterwards described in greater detail by Vesalius, who nevertheless appears not to have been aware of the important use which might be made of this knowledge. It was Michael Servet or Servetus, a Spanish monk, who in his treatise de Trinitatis Erroribus, published at Basil in 1531, or, according to Sprengel, in 1552, first maintained the imperviousness of the septum, and the transition of the blood by what he terms an unknown route, namely, from the right ventricle by the vena arteriosa (pulmonary artery) to the lungs, and thence into the arteria venosa or pulmonary vein, and left auricle and ventricle, from which, he adds afterwards, it is conveyed by the aorta to all parts of the body. Though the leading outlines, not only of the pulmonary
---
1 Born in 1569; burnt in 1553. 2 The passage of Servetus is so interesting that our readers may feel some curiosity in perusing it in the language of the author; and it is not unimportant to remark, that Servetus appears to have been led to think of the course of the blood, by the desire of explaining the manner in which the animal spirits were supposed to be generated. "Vitalis spiritus in sinistro cordis ventriculo assam originem habet, juvenilibus maxime pulmonibus ad ipsum perfectionem. Est spiritus tenuis, caloris vi elaboratus, flavo colore, ignea potentia, ut sit quasi ex puriore sanguine lucens, vapor substantiam continens aquae, aeris, et ignis. Generatur ex facto in pulmone connexione inspirati aeris et exhalingi. Fit autem communicatio hæc, non per parietem cordis medium, ut vulgo creditur, sed magno artificio a dextro cordis ventriculo, lacero per pulmones ductu agitatior sanguis subtilis; a palpitibus preparatur, flatus efficitur, et a vena arteriosa in arteriam venosam transfusitur. Deinde in ipsa arteria venosa, inspirato aeri miscetur, et expirante a foligine expurgatur; atque ita tandem a sinistro cordis ventriculo totum mixtum per diastolen attribatur, apta supellex, ut fiat spiritus vitalis. Quid ita per pulmones fit communicatio et preparatio, docet conjunctio varia, et communicatio venæ arteriosæ cum arteria venosa in pulmonibus. Confirmat hoc magnitudine insignis venæ arteriosæ, quæ nec tali nec tanta esset facta, nec tantam a corde ipsæ vim purissimæ sanguinis in pulmones emitteret, ob solam eorum nutrimentum, nec cor pulmonibus hac ratione serviret, cum praestantiam in embryone deferent pulmones ipsi alunde nutriant, ob membranulas illas seu valvas cordis, usque ad horum nativitatem; ut docet Galenus, &c. Itaque illa spiritus a sinistro cordis ventriculo arterias totius corporis decinde transfusitur, ita ut qui tenuior est, superiore petit, ubi magis elaboratur, praecipue in plexu retiformi, sub basi cerebri sito, ubi ex vitali flori incipit animalis, ad primum rationalis animæ rationem accedens." (De Trinitate, lib. v.) History, or small, but even of the great circulation, were sketched thus early by one who, though a philosopher, was attached to the church; it was only in his work *De Re Anatomica*, published at Venice in 1559, that Columbus formally and distinctly announced the circular course of the blood as a discovery of his own; and maintained, in addition to the imperviousness of the septum, the fact that the arteria re-alias (pulmonary vein) contains not air, but blood mixed with air brought from the lungs to the left ventricle of the heart, to be distributed through the body at large.
Soon after, views still more complete of the small or pulmonary circulation were given by Andrew Casalpinus of Arezzo, who not only maintained the analogy between the structure of the arterious vein or pulmonary artery and the aorta, and that between the venous artery or pulmonary veins, and veins in general, but was the first to remark the swelling of veins below ligatures, and to infer from it a reflex motion of blood in these vessels. The discoveries of Aranzi and Eustachius in the vessels of the fetus, tended at first to perplex, and afterwards to elucidate some of these notions. At length it happened, that between the years 1598 and 1600, a young Englishman, pursuing his anatomical studies at Padua under Fabricius of Aquapendente, learnt from that anatomist the existence of the valves in the veins of the extremities, and undertook to ascertain the use of these valves by experimental inquiry. It is uncertain whether he learnt from the writings of Casalpinus the fact observed by that author, of the tumescence of a vein below the ligature; but he could not fail to be aware, and indeed he shows that he was aware, of the small circulation as taught by Servetus and Columbus. Combining these facts already known, he, by a series of well-executed experiments, demonstrated clearly the existence, not only of the small, but of a general circulation from the left side of the heart by the aorta and its subdivisions, to the right side by the veins. This memorable truth was first announced in the year 1619.
It belongs not to this place, either to consider the arguments and facts by which Harvey defended his theory, or to notice the numerous assaults to which he was exposed, and the controversies in which his opponents wished to involve him. It is sufficient to say, that after the temporary ebullitions of spleen and envy had subsided, the doctrine of the circular motion of the blood was admitted by all enlightened and unprejudiced persons, and finally was universally adopted, as affording the most satisfactory explanation of many facts in anatomical structure which were either misunderstood or entirely overlooked. The inquiries to which the investigation of the doctrine gave rise produced numerous researches on the shape and structure of the heart and its divisions, of the lungs, and of the blood-vessels and their distribution. Of this description were the researches of Nicolas Steno on the structure of the heart, the classical work of Richard Lower, the dissertation of Pechlin, the treatise of Vieussens, the work of Malpighi on the structure of the lungs, several sketches in the writings of Mayow, and other treatises of less moment. Systematic treatises of anatomy began to assume a more instructive form, and to breathe a more philosophical spirit. The great work of Adrian Spigelius, which appeared in 1627, two years after the death of the author, contains indeed no proof that he was aware of the valuable generalization of Harvey; but in the institutions of Caspar Bartholin, as republished and improved by his son Thomas in 1651, the anatomical descriptions and explanations are given with reference to the new doctrine. A still more unequivocal proof of the progress of correct anatomical knowledge was given in the lectures delivered by Peter Dionis, at the Jardin Royal of Paris, in 1673 and the seven following years, in which that intelligent surgeon gave most accurate demonstrations of all the parts composing the human frame, and especially of the heart, its auricles, ventricles, and valves, and the large vessels connected with it and the lungs. These demonstrations, first published in 1690, were so much esteemed, that they underwent in the space of 30 years seven editions, were translated into English, and formed for a long time the best and only anatomical system in Europe.
The progress of anatomical discovery continued in the mean time to advance. In the course of the 16th century, Eustachius, in studying minutely the structure of the *vena azygos*, had recognised in the horse a white vessel full of watery fluid, connected with the internal jugular vein, on the left side of the vertebral column, corresponding accurately with the vessel since named *thoracic duct*. Fallopius also described vessels belonging to the liver, distinct from arteries and veins; and similar vessels appear to have been noticed by Nicolaus Massa. The nature and properties of these vessels were, however, entirely unknown. On the 23rd July 1622 Gaspar Asellius, professor of anatomy at Pavia, while engaged in demonstrating the recurrent nerves in a living dog, first observed numerous white delicate filaments crossing the mesentery in all directions; and though he took them at first for nerves, the opaque white fluid which they shed quickly convinced him that they were a new order of vessels. The repetition of the experiment the following day showed that these vessels were best seen in animals recently fed; and as he traced them from the villous membrane of the intestines, and observed the valves with which they were liberally supplied, he inferred that they were genuine chyliferous vessels. By confounding them with the lymphatics, he made them proceed to the pancreas and liver,—a mistake which appears to have been first rectified by Francis De le Boe. The discovery of Asellius was announced in 1627; and the following year, by means of the zealous efforts of Nicolas Peiresc, a liberal senator of Aix, the vessels were seen in the person of a felon who had eaten copiously before execution, and whose body was inspected an hour and a half after. In 1629 they were publicly demonstrated at Copenhagen by Simon Pauli; and the same year the thoracic duct was observed by Mentel for the first time since it was described by Eustachi. Five years after (1634), John Wesling, professor of anatomy and surgery at Venice, gave the first delineation of the lacteals from the human subject, and evinced more accurate knowledge than his predecessors, of the thoracic duct and the lymphatics. Highmore in 1637 demonstrated unequivocally the difference between the lacteals and the mesenteric veins; and though some perplexity was occasioned by the discovery of the pancreatic duct by Wirsung, yet this mistake was corrected by Thomas Bartholin; and the discovery by Pecquet in 1647, of the common trunk of the lacteals and lymphatics, and of the course which the chyle follows to reach the blood, may be regarded as the last of the series of isolated facts by the generalization of which the extent, distribution, and uses of the most important organs of the animal body were at length developed.
To complete the history of this part of anatomical science one step yet remained,—the distinction between the lacteals and lymphatics, and the discovery of the termination of the latter order of vessels. The honour of this discovery is divided between Jolyffe, an English anatomist, and Olaus Rudbeck, a young Swede. The former, according to the testimony of Glisson and Wharton, was aware of the distinct existence of the lymphatics in 1650, History and demonstrated them as such in 1652. It is nevertheless doubtful whether he knew them much before the latter period; and it is certain that Rudbeck observed the lymphatics of the large intestines, and traced them to glands, on the 27th January 1651, after he had, in the course of 1650, made various erroneous conjectures regarding them, and, like others, attempted to trace them to the liver. The following year he demonstrated them in presence of Queen Christina, and traced them to the thoracic duct, and the latter to the subclavian vein. Their course and distribution were still more fully investigated by Thomas Bartholin, Wharton, Swammerdam, and Blaes, the two last of whom recognised the existence of valves; while Antony Nuck of Leyden, by rectifying various errors of his predecessors, and adding several new and valuable observations, rendered this part of anatomy much more precise than formerly.
After this period anatomists began to study more accurately organs and textures already known, and to obtain more precise knowledge of the intimate structure and organization of the human body. Francis Glisson distinguished himself by a minute description of the liver, and a clearer account of the stomach and intestines than had yet been given. Thomas Wharton investigated the structure of the glands with particular care; and though rather prone to indulge in fanciful generalization, he developed some interesting views of these organs; while Charleton, who appears to have been a person of great genius, though addicted to hypothesis, made some good remarks on the communication of the arteries with the veins, the fetal circulation, and the course of the lymphatics. But the circumstance which chiefly distinguished the history of anatomy at the beginning of the seventeenth century, was the appearance of Thomas Willis, who rendered himself eminent not only by the first good researches on the brain and nerves, but by many judicious observations on the structure of the lungs, the intestines, the blood-vessels, and the glands. His anatomy of the brain and nerves is so minute and elaborate, and abounds so much in new information, that the reader is struck by the immense chasm between the vague and meagre notices of his predecessors, and the ample and correct descriptions of Willis. This excellent work, however, is not the result of his own personal and unaided exertions; and the character of Willis derives additional lustre from the candid avowal of his obligations to Wren and Millington, and, above all, to the diligent researches of his fellow-anatomist Richard Lower.
Willis was the first who correctly numbered the nerves, and described their origins in the order in which they have been generally named till the recent improvements of Soemmerring. His observation of the connection of the eighth pair with the slender nerve which issues from the beginning of the spinal chord is known to all. He remarked the parallel lines of the mesolobe, afterwards minutely described by Vieq d'Azyr. He seems to have recognised the communication of the convoluted and figurate surfaces of the brain, and that between the lateral cavities beneath the fornix. He designates the objects of the central surface—the anterior as the lentiform eminences, with the striated appearance of their internal substance—the posterior as the optic chambers or thalami; the four orbicular eminences, with the bridge, which he first named annular protuberance; and the white psiform bodies, since called mammillary eminences, behind the infundibulum. In the cerebellum he remarks the arborescent arrangement of the white and grey matter, and gives a good account of the internal carotids, and the communications which they make with the branches of the basilar artery. Wepfer had already demonstrated the peculiar curvature of History, the former vessels in the carotid canal, and refuted the fiction of the rete mirabile.
About the same time the researches of Malpighi tended greatly to improve the knowledge of minute structure. He gave the first distinct ideas on the organization of the lung, and the mode in which the bronchial tubes and vessels terminate in that organ. By the microscope he traced the transition of the arteries into the veins. He examined the omentum, and inquired into the manner in which fat and marrow are secreted. He endeavoured to unfold, by dissection and microscopic observation, the minute structure of the brain. He demonstrated the organization of the skin, and considered its constituents as the organ of touch. He studied the structure of bone, and rectified the errors of Gagliardi; he traced the formation and explained the structure of the teeth; and he finally carried his researches into the substance of the liver, the spleen, the kidneys, and the conglomerate glands. In these difficult inquiries the observations of Malpighi are in general faithful, and his descriptions are accurate. He may be regarded as the founder of that part of anatomical science which treats of structure and organization; and, even in the present day, his writings are both interesting and instructive.
Nicolas Steno described with accuracy the lacrymal gland and passages, and re-discovered the parotid duct. Bellini studied the structure of the kidneys, and described the tongue and tonsils with some care; and Drelincourt laboured to investigate the changes effected on the uterus by impregnation, and to elucidate the formation of the fetus. The science might have derived still greater advantages from the genius of Regnier de Graaf, who investigated with accuracy the structure of the pancreas and of the organs of generation in both sexes, had he not been cut off at the early age of 32. Lastly, Wepfer, though more devoted to morbid anatomy, made, nevertheless, some just observations on the anatomical disposition of the cerebral vessels, the glandular structure of the liver, and the termination of the common duct in the duodenum.
The appearance of Frederic Ruysch, who was born in 1638, and became professor of anatomy at Amsterdam in 1665, gave a new impulse to anatomical research, and tended not only to give the science greater precision, but to extend its limits in every direction. The talents of Ruysch are said to have been developed by accident. To repel the audacious and calumniating aspersions with which De Bils attacked De le Boe and Van Horne, Ruysch published his tract on the valves of the lymphatics, which completely established his character as an anatomist of originality and research. This, however, is the smallest of his services to the science. The art of injecting, which had been originally attempted by Eustachi and Varoli, and was afterwards rudely practised by Glisson, Bellini, and Willis, was at length carried to greater perfection by De Graaf and Swammerdam, the former of whom injected the spermatic vessels with mercury and variously coloured liquors, while the latter, by employing melted wax with other ingredients, made the first approach to the refinements of modern anatomy. By improving this idea of using substances, which, though solid, may be rendered fluid at the period of injecting, Ruysch carried this art to the highest perfection.
By the application of this happy contrivance, he was enabled to obtain more correct views than his predecessors of the arrangement of minute vessels in the interior of organs, and to demonstrate peculiarities of organization which escaped the scrutiny of previous anatomists. Scarc- ly a part of the human body eluded the penetration of his syringe; and his discoveries were proportionally great. His account of the valves of the lymphatics, of the vessels of the lungs, and their minute structure; his researches on the vascular structure of the skin, of the bones, and their epiphyses, and their mode of growth and union; his observations on the spleen, the glans penis, the clitoris, and the womb impregnated and unimpregnated, were sufficient to give him the reputation of a skilful and accurate anatomist. These, however, were but a limited part of his anatomical labours. He studied the minute structure of the brain; he demonstrated the organization of the choroid plexus; he described the state of the hair when affected with Polish plait; he proved the vascular structure of the teeth; he injected the dura mater, the pleura, the pericardium, and peritoneum; he unfolded the minute structure of the conglomerate glands; he investigated that of the synovial apparatus placed in the interior of the joints; and he discovered several curious particulars relating to the lacteals, the lymphatics, and the lymphatic glands. So assiduously, indeed, did Ruysch study by injection the tissue of the organs of the animal body, that it is less easy to say what he did than what he neglected. To him we are indebted for many of the facts of which anatomy at the present day consists. The success of his injections, however, though it enabled him to trace the most delicate terminations of vessels in the substance of organs, perhaps exercised an unfavourable bias in making him look for vessels exclusively in the minute structure of all the tissues.
Meanwhile, Meibomius re-discovered the palpebral glands, which were known to Casserius; Swammerdam studied the action of the lungs, described the structure of the human uterus, and made numerous valuable observations on the cæca and pancreatoid organs of fishes; and Kerckringius attempted to explain the process of ossification, and determine its different stages. John Conrad Brunner, in the course of experiments on the pancreas, discovered the muciparous glands of the duodenum,—a fact to which Conrad Peyer gave a more generalized character by his description of the muciparous glands of the intestinal canal at large. Leonard Tassin, distinguished for original observation, rendered the anatomical history of the brain more accurate than heretofore, and gave particular accounts of the intestinal tube, the pancreatic duct, and the hepatic ligaments. About the same time much light was thrown on the intimate constitution of several of the tissues, and on the minute communications of the arterial and venous tubes by the microscopical observations of Leeuwenhoek.
That France might not be without participation in the glory of advancing the progress of anatomical knowledge, the names of Duverney and Vieussens are commemorated with distinction. The former, born in 1648, and first introduced into public life in 1676 in the Royal Academy of Sciences, decorated with the honorary title of professor of anatomy to the Dauphin, and appointed in 1679 professor at the Jardin Royal, distinguished himself by the first accurate account of the organ of hearing, and by his dissections of several animals at the academy, supplied valuable materials for the anatomical details of the natural history of animals published by that learned body. He appears to have been the first who demonstrated the fact, that the cerebral sinuses open into the jugular veins, and to have been aware that the former receive the veins of the brain, and are the venous receptacles of the organ. He understood the cerebral cavities, and their mode of communication; distinguishes the posterior pillars of the vault from the pedes hippocampi; recognises the two plates of the septum lucidum; and, what is still more remarkable, he first indicates distinctly the crossing or plaiting of the cerebral chords in the linear furrow between the right and left pyramidal bodies—a fact afterwards verified by the researches of Mistichelli, Petit, and Santorini. He studied the ganglions attentively, and gives the first distinct account of the formation, connections, and distribution of the intercostal nerve. It is interesting to remark, that his statement that the veins or sinuses of the spinal chord terminate in the rena azygos has been verified by the recent researches of Dupuytren and Breschet, which show that the vertebral veins communicate by means of the intercostal and superior lumbar veins with the azygos and demi-azygos. His account of the structure of bones, and of the progress of ossification, is valuable. He recognised the vascular structure of the spleen; and he gives a correct account of the excretory ducts of the prostate gland, the verumontanum, and the anteprostates.
One of the circumstances which the history of this period of anatomical science shows tended considerably to its improvement, is the attention with which Comparative Anatomy was beginning to be cultivated. In ancient times, and at the revival of letters, the dissection of the lower animals was substituted for that of the human body; and the descriptions of the organs of the latter were too often derived from the former. The obloquy and contempt in which this abuse involved the study of animal anatomy made it be neglected, or pursued with indifference, for more than two centuries, during which anatomists confined their descriptions, at least very much, to the parts of the human body. At this period, however, the prejudice against Comparative Anatomy began to subside; and animal dissection, though not substituted for that of the human body, was employed, as it ought always to have been, to illustrate obscurities, to determine doubts, and to explain difficulties, and, in short, to enlarge and rectify the knowledge of the structure of animal bodies generally.
For this revolution in its favour, Comparative Anatomy was in a great measure indebted to the learned societies which were established about this time in the different countries of Europe. Among these the Royal Society of London, embodied by charter by Charles II. in 1660, and the Academy of Sciences of Paris, founded in 1665 by Colbert, are undoubtedly entitled to the first rank. Though later in establishment, the latter institution was distinguished by making the first great efforts in favour of Comparative Anatomy; and Perrault, Pequet, Duverney, and Mery, by the dissections of rare animals obtained from the royal menagerie, speedily supplied valuable materials for the anatomical naturalist. In England, Nehemiah Grew, Edward Tyson, and Samuel Collins, cultivated the same department with diligence and success. The first has left an interesting account of the anatomical peculiarities of the intestinal canal in various animals; and the second, in the dissection of a porpoise, an opossum, and an orang outang, adduces some valuable illustrations of the comparative differences between the structure of the human body and that of the lower animals. To the third belongs the merit of conceiving, and executing on an enlarged plan, a comprehensive system, embodying all the information then extant. With the aid of Tyson and his own researches, which were both extensive and accurate, he composed a system of anatomical knowledge, in 1685, which he not only delivers ample and accurate descriptions of the structure of the human body, and the various morbid changes to which the organs are liable, but illustrates the whole by accurate and interesting sketches of the peculiarities of the lower animals. The matter of this work History, is so excellent, that it can only be ascribed to ignorance that it has received so little attention. Though regarded as a compilation, and though indeed much of the human anatomy is derived from Vesalius, it has the advantage of the works published on the Continent at that time, that it embodies most of the valuable facts derived from Malpighi, Willis, and Vieussens. The Comparative Anatomy is almost all original, and acquired from personal research and dissection; and the pathological observations, though occasionally tinged with the spirit of the times, show the author to have been endowed with the powers of observation and judicious reflection in no ordinary degree.
About this time also we recognise the first attempts to study the minute atomic constitution of the tissues, by the combination of the microscope and the effects of chemical agents. Bone furnished the first instance in which this method was put in use; and though Gagliardi, who undertook the inquiry, had fallen into some mistakes which it required the observation of Malpighi to rectify, this did not deter Clopton Havers and Nesbitt, in England, and Courtial, Du Hamel, and Delasone, and afterwards Herissant, in France, from resuming the same train of investigation. The mistakes into which these anatomists fell belong to the imperfect method of inquiry. The facts which they ascertained have been verified by recent experiment, and constitute no unessential part of our knowledge of the structure of bone.
Ten years after the publication of the work of Collins, Henry Ridley, another English anatomist, distinguished himself by a monograph on the brain, which, though not free from errors, contains nevertheless some valuable observations. Ridley is the first who distinguishes by name the restiform processes, or the posterior pyramidal eminences. He recognised the figure of the four eminences in the human subject; he remarked the mammillary bodies; and he discovered the sinus which passes under his name.
Raymond Vieussens, by the publication of his great work on neurography in 1684, threw new light on the configuration and structure of the brain, the spinal chord, and the nerves; and gave a description of the arrangement and distribution of the latter more precise than heretofore. Of the formation and connections of the sympathetic nerve especially he gave views which have been generally adopted by subsequent anatomists. His new arrangement of the vessels, published in 1705, contains several curious and some hypothetical opinions. His observations on the structure of the heart, published in 1706, and enlarged in 1715, exhibit the first correct views of the intimate structure of an organ, which afterwards was most fully developed by the labours of Lancisi and Senac. His treatise on the ear is not superior to that of Duverney.
To this same period belong the rival publications of Godfrey Bidloo and William Cowper, the last of whom, however, stained a reputation otherwise good, by publishing as his own the engravings of the former. Cowper further distinguished himself by a minute account of the urethral glands, already known to Columbus and Mery; a good description of the intestinal glands, discovered by Brunner and Peyer; and by demonstrating the communication of the arteries and veins of the mesentery.
The anatomical genius of Italy, which had slumbered since the death of Malpighi, was destined once more to revive in Lancisi, Valsalva, and his illustrious pupils Santorini and Morgagni. Valsalva especially distinguished himself by his description of the structure of the ear, which, in possessing still greater precision and minuteness than that of Duverney, is valuable in setting the example of rendering anatomy altogether a science of description.
Santorini, who was professor at Venice, was no unworthy friend of Valsalva and Morgagni. His anatomical observations, which relate to the muscles of the face, the brain, and several of the nerves, the ducts of the lacrymal gland, the nose and its cavities, the larynx, the viscera of the chest and belly, and the organs of generation in the two sexes, furnish beautiful models of essays distinguished for perspicuity, precision, and novelty, above any thing which had then appeared. These observations, indeed, which bear the impress of accurate observation and clear conception, may be safely compared with any anatomical writings which have appeared since. Those on the brain are particularly interesting. Morgagni, though chiefly known as a pathological anatomist, did not neglect the healthy structure. His *Adversaria*, which appeared between 1706 and 1719, and his *Epistles*, published in 1728, contain a series of observations to rectify the mistakes of previous anatomists, and to determine the characters of the healthy structure of many parts of the human body. Many parts he describes anew, and indicates facts not previously observed. All his remarks show how well he knew what true anatomical description ought to be. In this respect, indeed, the three anatomists now mentioned may be said to have anticipated their contemporaries nearly a century; for, while other authors were satisfied with giving loose and inaccurate or meagre notices of parts, with much fanciful supposition, Valsalva, Santorini, and Morgagni, laboured to determine with precision the anatomical characters of the parts which they describe.
The same character is due to Winlow, a native of Denmark, but, as pupil and successor of Duverney, as well as a convert to Catholicism, naturalized in France, and finally professor of anatomy at the Royal Garden. His exposition of the structure of the human body is distinguished for being not only the first treatise of descriptive anatomy, divested of physiological details and hypothetical explanations foreign to the subject, but for being a close description derived from actual objects, without reference to the writings of previous anatomists. About the same time Cheselden in London, the first Monro in Edinburgh, and Albinius in Leyden, contributed by their several treatises to render anatomy still more precise as a descriptive science. The *Osteographia* of the former was of much use in directing attention to the study of the skeleton, and the morbid changes to which it is liable. This work, however, magnificent as it was, was excelled by that of Albinius, who, in 1747, published engravings descriptive of the bones and muscles, which, perhaps, will never be surpassed either in accuracy of outline or beauty of execution. The several labours of this author, indeed, constitute an important era in the history of the science. He was the first who classified and exhibited the muscles in a proper arrangement, and applied to them a nomenclature which is still retained by the consent of the best anatomists. He gives a luminous account of the arteries and veins of the intestines, represents with singular fidelity and beauty the bones of the fetus, inquires into the structure of the skin, and the cause of its colour in different races; represents the changes incident to the womb in different periods of pregnancy, and describes the relations of the thoracic duct and the *vena cava* with the contiguous parts. Besides these large and magnificent works, illustrated by the most beautiful engravings, six books of *Academical Annotations* were the fruits of his long and assiduous cultivation of anatomy. These contain valuable remarks on the sound structure and morbid deviations of numerous parts of the human body.
To render the knowledge of the skeleton more complete, Duhamel and Delasone studied the minute structure of bone, and the process of ossification; William Hunter and Herissant investigated the texture of the cartilages and ligaments. M. Lieutaud also, who had already laboured to rectify many errors in anatomy, described with much accuracy the structure and relations of the heart and its cavities, and rendered the anatomy of the bladder very precise, by describing the triangular space and the mammillary eminence at its neck.
Albinus found a worthy successor in his pupil Albert Von Haller, who, with a mind imbued with every department of literature and science, directed his chief attention, nevertheless, to the cultivation of anatomical and physiological knowledge. Having undertaken at an early age (21) to illustrate, with commentaries, the physiological prelections of his preceptor Boerhaave, he devoted himself assiduously to the perusal of every work which could tend to facilitate his purpose; and as he found numerous erroneous or imperfect statements, and many deficiencies to supply, he undertook an extensive course of dissection of human and animal bodies, to obtain the requisite information. For 17 years, during which he was professor at Goettingen, he dissected 400 bodies, and inspected their organs with the utmost care. The result of these assiduous labours appeared at intervals in the form of dissertations by himself, or under the name of some one of his pupils, finally published in a collected shape, between 1746 and 1751 (Disputationes Anatomicae Selectiores); and in eight numbers of most accurate and beautiful engravings, representing the most important parts of the human body, e.g. the diaphragm, the uterus, ovaries and vagina, the arteries of the different regions and organs, with learned and critical explanatory observations. Some years after, when he had retired from his academical duties at Goettingen, he published, between 1757 and 1765, the large and elaborate work which, with singular modesty, he styled Elements of Physiology. This work, though professedly devoted to the latter science, rendered nevertheless the most essential services to the former. Haller, drawing an accurate line of distinction between the two, gave the most clear, precise, and complete descriptions of the situation, position, figure, component parts, and minute structure of the different organs and their appendages. The results of previous and coeval inquiry, obtained by extensive reading, he sedulously verified by personal observation; and though he never rejected facts stated on credible authorities, he in all cases laboured to ascertain their real value by experiment. The anatomical descriptions are on this account not only the most valuable part of his work, but the most valuable that had then or for a long time after appeared; and it is perhaps a sufficient proof of their intrinsic merit, that they are still resorted to by the anatomist as the most faithful guide to many of his researches. It is painful, nevertheless, to think, that the very form in which this work is composed, with copious and scrupulous reference to authorities, made it be regarded as a compilation only; and that the author was compelled to show, by a list of his personal researches, that the most learned work ever given to the physiologist, was also the most abundant in original information.
With the researches of Haller, it is proper to notice those of his contemporary, John Frederick Meckel, and his pupil John Godfrey Zinn. The former, who was professor of anatomy at Berlin, described with unrivalled accuracy the Gasserian ganglion, the first pair of nerves and its distribution, and that of the facial nerves generally, and discovered the sphenopalatine ganglion. He made some original and judicious observations on the tissue of the skin and the mucous net; and above all, he recognised the connection of the lymphatic vessels with the veins,—a doctrine which, though neglected, has been lately revived by Fohmann and Lippi. He also collected several valuable observations on the morbid states of the heart and brain. At the same time Zinn, who was professor of medicine at Goettingen, published on the eye a classical treatise, which demonstrated at once the defects of previous inquiries, and how much it was possible to elucidate, by accurate research and precise description, the structure of one of the most important organs of the human frame. As a general proof of the extraordinary merit of this work, it is sufficient to say, that in critical learning and descriptive accuracy it has not been equalled, and probably will never be surpassed. It was re-published after his death by Wrisberg.
General anatomy, and the study of the atomic constitution of the tissues which had originally been commenced by Leeuwenhoek, Malpighi, and Ruysch, began at this period to attract more general attention. De Bergen had already demonstrated the general distribution of cellular membrane, and shown that it not only incloses every part of the animal frame, but forms the basis of every organ,—a doctrine which was adopted, and still more fully expanded, by his friend Haller, in opposition to what was asserted by Albinus, who maintains that each part has a proper tissue. William Hunter at the same time gave a clear and ingenious statement of the difference between cellular membrane and adipose tissue, in which he maintained the general distribution of the former, and represented it as forming the serous membranes, and regulating their physiological and pathological properties,—doctrines which were afterwards confirmed by his brother John Hunter. A few years after, the department of general anatomy first assumed a substantial form, in the systematic view of the membranes and their mutual connections traced by Andrew Bonn of Amsterdam. In his inaugural dissertation De Continuationibus Membranarum, published at Leyden in 1763, this author, after some preliminary observations on membranes in general and their structure, and an exposition of that of the skin, traces its transition into the mucous membranes and their several divisions. He then explains the distribution of the cellular membrane and the aponeurotic expansions, and the periosteum and perichondrium, by either of which, he shows, every bone of the skeleton is invested and connected. He finally gives a very distinct view of the arrangement of the internal membranes of cavities, those named serous and fibro-serous, and the manner of their distribution over the contained organs. This essay, which is a happy example of generalization, is remarkable for the interesting general views of the structure of the animal body which it exhibits; and to Bonn belongs the merit of sketching the first outlines of that system which it was reserved for the genius of Bichat to complete and embellish. Lastly, Bordeu, in an elaborate essay on the mucous tissue, or cellular organ, as he terms it, brought forward some interesting views of the constitution, nature, and extent of the cellular membrane.
Though anatomy was hitherto cultivated with much success as illustrating the natural history and morbid states of the human body, yet little had been done for the elucidation of local diseases, and the surgical means by
---
1 "Pene quadrigenitis mea manu dissecitis hemimum cadaveribus." (Prefatio ad tom. vi. Elementorum Physiologici.) 2 Ibid. 3 Annal. Acad. Leh. lil. p. 2. History, which they may be successfully treated. The idea of applying anatomical knowledge directly to this purpose appears to have originated with Bernardus Genga, a Roman surgeon, who published in 1672, at Rome, a work entitled Surgical Anatomy, or the Anatomical History of the Bones and Muscles of the Human Body, with the description of the Blood-vessels. This work, which reached a second edition in 1687, is highly creditable to the author, who appears to have studied intimately the mutual relations of different parts. It is not improbable that the example of Genga led Palfyn, a surgeon at Ghent, to undertake a similar task about 30 years after. For this, however, he was by no means well qualified; and the work of Palfyn, though bearing the name of Surgical Anatomy, is a miserable compilation, meagre in details, inaccurate in description, and altogether unworthy of the honour of being republished, as it afterwards was, by Antony Petit.
While these two authors, however, were usefully employed in showing what was wanted for the surgeon, others were occupied in the collection of new and more accurate facts. Albinus, indeed, ever assiduous, had, in his account of the operations of Rau, given some good sketches of the relative anatomy of the bladder and urethra; and Cheselden had already, in his mode of cutting into the urinary bladder, shown the necessity of exact knowledge of the relations of contiguous parts. The first decided application, however, of this species of anatomical research it was reserved for a Dutch anatomist of the 18th century to make. Peter Camper, professor of Anatomy at Amsterdam, published in 1760 and 1762 his anatomo-pathological demonstrations of the parts of the human arm and pelvis, of the diseases incident to them, and the mode of relieving them by operation. These observations are of the utmost value. The situation of the blood-vessels, nerves, and important muscles, is explained with the greatest clearness; and though the engravings are rather bold and accurate than elegant, they constitute a work indispensable to the anatomical reader. His remarks on the lateral operation of lithotomy, which contain all that was then known on the subject, are exceedingly interesting and valuable to the surgeon. It appears further that he was the first who examined anatomically the mechanism of ruptures, his delineations of which were published in 1801 by Soemmering.
It had been originally observed by Riolan, Severinus, Rudbeck, Harvey, and De Graaf, that in the fetus the testicles are situate in the abdomen; but this observation, so pregnant with important results, appears to have been overlooked, nay doubted, till verified by Haller, who showed that their removal from this region is connected with the formation of congenital hernia. The situation of the testicles previous to birth, their gradual descent into the scrotum, and the mode in which a portion of intestine may slip down with them, was still more fully investigated by William Hunter, by Camper, and finally by John Hunter; and the peculiarities of the inguinal canal, and the manner in which its persistence after birth, or its re-opening, may occasion hernial protrusions, have been well explained by Sandifort, Scarpa, Sir Astley Cooper, Allan Burns, and Lawrence, and more recently by Hesselbach and Langenbeck.
The attention of anatomists was now directed to the elucidation of the most obscure and least explored parts of the human frame—the lymphatic vessels and the nerves. Although, since the first discovery of the former by Asellius, Rudbeck, and Persquet, much had been done, especially by Ruysch, Nuck, Meckel, and Haller, many points, notwithstanding, relating to their origin, and distribution in particular organs, and in the several classes of animals, were imperfectly ascertained or entirely unknown. William Hunter investigated their arrangement, and proposed the doctrine that they are absorbents; and John Hunter, who undertook to demonstrate the truth of this hypothesis by experiment, discovered, in 1758, lymphatics in birds in the neck. As this doctrine required the existence of this order of vessels, not only in quadrupeds and birds, but in reptiles and fishes, the inquiry attracted attention among the pupils of Hunter; and William Hewson at length communicated, in December 1768, to the Royal Society of London, an account of the lacteals and lymphatics in birds, fishes, and reptiles, as he had discovered and demonstrated them. The subject appears about the same time to have been investigated by the second Monro, who indeed claimed the merit of discovering these vessels in the classes of animals now mentioned. But whatever researches this anatomist may have instituted, Hewson, by communicating his observations to the Royal Society, must be allowed to possess the strongest as well as the clearest claim to discovery. The same author, in 1774, gave the first complete account of the anatomical peculiarities of the lymphatic system in man and other animals, and thereby supplied an important gap in this department. Hewson is the first who distinguishes the lymphatics into two orders, the superficial and the deep, both in the extremities and in the internal organs. He also studied the structure of the intestinal villi, in which he verified the observations of Lieberkühn; and in inquiring into the minute structure of the glands, he adopted the views of Ruysch. He finally applied his anatomical discoveries to explain many of the physiological and pathological phenomena of the animal body. Ten years after, John Sheldon, another pupil of Hunter, gave a second history and description of the lymphatics, which, though divested of the charm of novelty, contains many interesting anatomical facts. He also examined the structure of the villi.
Lastly, Cruikshank, in 1786, published a valuable history of the anatomy of the lymphatic system, in which he maintains the accuracy of the Hunterian doctrine, that the lymphatics are the only absorbents; gave a more minute account than heretofore of these vessels, of their coats and valves; and supplied the defect left by Hewson, by explaining the structure of the lymphatic glands. He also injected the villi, and examined them microscopically, verifying most of the observations of Lieberkühn. The origin of the lymphatics he maintains rather by inference than direct demonstration. To these three works, though in other respects very excellent, it is a considerable objection that the anatomical descriptions are much mixed with hypothetical speculation and reasonings on properties, and that the facts are by no means always distinguished from mere matters of opinion. At the same time Haase published an account of the lymphatics of the skin and intestines, and the plexiform nets of the pelvis.
To complete this sketch of the history of the anatomy of the lymphatic system, it may be added that Mascagni, who had been engaged from the year 1777 to 1781 in the same train of investigation, first demonstrated to his pupils several curious facts relating to the anatomy of the lymphatic system. When at Florence in 1782, he made several preparations, at the request of Peter Leopold, grand duke of Tuscany; and when the Royal Academy of Sciences at Paris announced the anatomy of this system for their prize essay appointed for March 1784, Mascagni resolved on communicating to the public the results of his researches—the first part of his commentary, with four engravings. Anxiety, however, to complete his preparations detained him at Florence till the close of 1785; and from these causes his work did History, not appear till 1787. These delays, however, unfavourable as they were to his claims of priority to Sheldon and Cruikshank, were on the whole advantageous to the perfection of his work, which is not only the most magnificent, but also the most complete, that ever was published on the lymphatics. In his account of the vessels and their valves, he confirms some of Hewson's observations, and rectifies others. Their origins he proves by inference much in the same manner as Cruikshank; but he anticipates this author in the account of the glands, and he gives the most minute description of the superficial and deep lymphatics, both in the members and in the internal organs.
General accounts of the nerves had been given with various degrees of accuracy by Willis, Vieussens, Winslow, and the first Monro; and the subject had been much rectified and improved by the indefatigable Haller. The first example of minute descriptive neurography was given in 1748 by J. F. Meckel, whose account of the fifth pair, and their connection with the intercostal, and of the nerves of the face, will long remain a lasting proof of accuracy and research. The same subject was investigated in 1765 by Hirsch, and in 1777 by Wrisberg. In 1766 Metzger examined the origin, distribution, and termination of the first pair,—a point which was afterwards very minutely treated by Scarpa in his anatomical disquisitions published in 1780; and the internal nerves of the nostrils were examined in 1791 by Haase. The optic nerve, which had been studied originally by Varoli, and afterwards by Mery, Duverney, Henkel, Moeller, Hein, and Kaldschmid, was examined with extreme accuracy, with the other nerves of the organ of vision, by Zinn, in his elaborate treatise. The phrenic nerves, and the oesophageal branches of the eighth pair, were studied by Haase; the phrenic, the abdominal, and the pharyngeal nerves, by Wrisberg; those of the heart most minutely by Andersch; and the origins, formation, and distribution of the intercostal nerve, by Iwanoff, Ludwig, and Girardi. The labours of these anatomists, however, were eclipsed by the splendid works of Walter on the nerves of the chest and belly; and those of Scarpa on the distribution of the 8th pair, and splanchnic nerves in general. In minuteness of description, and in beauty of engraving, these works have not yet been equalled, and will never perhaps be surpassed. About the same time Scarpa, so distinguished in every branch of anatomical research, investigated the minute structure of the ganglions and plexuses.
The brain was also studied with great attention by Malacarne, Vicq d'Azyr, and Soemmerring; more recently Reil examined the minute structure of the organ and its component parts with unrivalled research and accuracy; and Rolando studied the structure of the cerebellum.
Lastly, the anatomy of the gravid uterus, which had been originally studied by Albinus, Roederer, and Smellie, was again illustrated most completely by William Hunter, whose engravings will remain a lasting memorial of scientific zeal and sculptorial talent.
The perfection which anatomical science has attained has been evinced during the last ten years of the eighteenth century, and the first half of the nineteenth century, in the improved character of the systems published by anatomists. The first who gave a good modern system was Sabatier; but his work was speedily eclipsed by the superior merits of Soemmerring, Bichat, and Portal. To the first belongs the character of being at once the most learned and critical, and at the same time the most precise, yet published. The General Anatomy of Bichat is a monument of his philosophical genius, which will last as long as the structure and functions of the human body are objects of interest. His Descriptive Anatomy is distinguished by clear and natural arrangement, precise and accurate description, and the general ingenuity with which the subject is treated. The physiological observations are in general correct, often novel, and always highly interesting. It is unfortunate, however, that the ingenious author was cut off prematurely during the preparation of the third volume. It must nevertheless be acknowledged, that if the two last ones betray the want of the genius of Bichat, they are pervaded with the general spirit by which the others are impressed, and are highly creditable to the learning, the judgment, and the diligence of MM. Roux and Buisson. The system of Portal is a valuable and correct digest of anatomical and pathological knowledge, which, in exact literary information, is worthy of the author of the History of Anatomy and Surgery, and, in accuracy of descriptive details, shows that M. Portal trusts not to the labours of his predecessors only. Since the appearance of these standard works, Meckel published a Manual, which combines the philosophical generalizations of Bichat with the precise description and pathological knowledge of Portal. Of this work a French translation was published at Paris in 1825. Lastly, Cloquet formed, on the model of the Descriptive Anatomy of Bichat, a system in which he avails himself of the literature and precision of Soemmerring, and the details of Portal. The system of Gordon is imperfect, its completion being interrupted by the death of the author; but, so far as it goes, it gives a correct summary of General Anatomy, and some accurate descriptive details of the heart and brain. The work of Dr Monro is entitled to mention in this place, as an elementary treatise, containing with anatomical description a good deal of physiological and pathological matter. These, however, must be considered foreign to the subject.
Of treatises on particular departments, those of Blumenbach on the bones, Innes and Sandifort on the muscles, the several anatomical writings and engravings of Charles Bell on the arteries, the nerves, and the brain, Barclay on the arteries, Tiedemann on the nerves of the uterus, and the same author's engraved delineations of the arteries, and Harrison's excellent work on the arteries, deserve notice. The most complete work, however, on the anatomy of the arteries was published at London between the years 1840 and 1844, by Richard Quain, Professor of Anatomy in London University College. In this work, Mr Quain has given with great accuracy, views of the normal origin, course, and distribution of all the important arteries of the human body; and has bestowed great attention in distinguishing and fixing all those which are normal from those which are abnormal. This work consists of eighty-seven most faithful lithographed engravings of large size, and is accompanied by 543 octavo pages of descriptive letterpress. From the attention with which it has been prepared, it ought long to continue a standard work on the anatomy of the arterial system.
The minute structure of bone which had been examined by Scarpa, was again studied by that indefatigable inquirer, and in this country by Howship. In 1834, Deutsch published at Breslau a dissertation containing some good observations on the minute structure of Bone; and in 1836, Miescher, with the aid of John Müller, published at Berlin a history of the general anatomy of bone, with some important observations on the canaliculi of Clopton Havers, and the manner in which the earthy matter is deposited in the bony texture. These observations, which were made by the aid of the microscope, form the basis of much of the modern knowledge on the structure of these organs.
On the minute structure of the teeth, the results of careful investigation were published by Retzius in 1837; by Alexander Nasmyth in 1839 and 1849; and by John Tomes in 1848; and the mode in which these organs are developed was elucidated with much skill in 1839 by Mr John Goodsir. The structure of the limes, which was investigated in 1808 by Reisseissen, in 1821 by Magendie, and in 1827 by Sir E. Home, was anew subjected to scrutiny in 1836 by Bourgery, in 1842 by Mr William Addison; in 1845 by Mr George Rainey; and in 1846 by M. Rossignol.
On the anatomy of the nervous system numerous treatises have appeared during the last forty years. Joseph and Charles Wenzel investigated in 1812 the minute structure of the brain in man and the lower animals; Tiedemann traced the development of the organ in the fetus, and rectified many errors on its formation and minute structure; Sir Everard Home and M. Bauer investigated its atomic constitution by the microscope. But this was done in a manner still more elaborate, and with improved means of observation, by Ehrenberg in 1833, by Valentin in 1834, by Remak in 1838, and by Purkinje about the same time. In 1836 Samuel Solly published an instructive treatise containing the anatomical history of the brain and its parts, elucidated chiefly after the method of demonstration proposed by Gall and Reil, and improved by Foville. A second edition of this work, enlarged and improved by much additional information, appeared in 1847; and though much of the volume is devoted to physiological and pathological matter, it may be regarded as the most complete treatise on the subject in the English language. More strictly anatomical, and not less valuable, is the Descriptive and Physiological Anatomy of the Brain, Spinal Chord, and Ganglions, by Robert Bentley Tod, published in 1845; a treatise remarkable for accuracy and precision in information.
Lobstein investigated in 1823 the structure and distribution of the Great Sympathetic Nerve; Bellingeri published the same year an accurate description of the Spinal Chord and its Nerves; Charles Bell, in his great work on the Nervous System, develops and establishes the truth of the ancient theory of the separate nature of the nerves of motion and those of sensation.
Between 1830 and 1834, Joseph Swan published a series of twenty-five excellent drawings, representing the connections, course, and distribution of all the demonstrable nerves of the human body, upon a scale as large as life; a work, the result of several years of personal dissection. Robert Lee gave in 1842 elaborate views of the position of the ganglia, and distribution of the Nerves of the Uterus in the virgin, and in the impregnated state; and the same parts were made the subject of investigation by Mr Snow Beck.
which, during the eighteenth century, was diligently cultivated by Daubenton, Pallas, Haller, John Hunter, and the second Monro, became during the first thirty years of the nineteenth century a subject of increased interest, from its intimate connection with the sciences of zoology, physiology, and geology, and has consequently been studied with great assiduity and skill by Cuvier, Dumeril, Home, Tiedemann, Meckel, Spix and Martius, Robert Grant, Rymer Jones, Richard Owen, and by numerous inquirers in the several countries of Germany.
The improvement which has been effected in the construction of the compound microscope during the thirty years subsequent to 1822, has contributed, in no small degree, to enable anatomists to obtain more correct information on the intimate structure of different organs and tissues of the animal body. For the first twenty years of the nineteenth century, opticians and instrument-makers had at intervals endeavoured to render the compound microscope at once an instrument of greater power, and more free from sources of error and optical illusion than it had hitherto been possible to obtain it. Two defects, however, still adhered to the compound microscope. The instrument was not achromatic; and a considerable degree of spherical aberration uncorrected rendered the image indistinct.
Between 1812 and 1815, Professor Amici of Modena had attempted to construct an achromatic object-glass of one single lens; but found that this was impracticable. M. Selligues of Paris, in 1823, after various trials, found that this could be done by making the object-glass consist of four achromatic compound lenses, each of which was composed of two single lenses. This method was carried into practice, and improved by the two MM. Chevalier of Paris. About the same time, Dr Goring in London, with the aid of Mr Tulley and Mr Pritchard, constructed compound microscopes upon a similar principle.
On the 5th of April 1824, M. Selligues presented to the Academy of Sciences a microscope, constructed by M. Chevalier, on the principle of combined lenses; and in the course of the same year, and without the knowledge of what had been done in France, the late Mr Tulley, at the suggestion of Dr Goring, constructed a compound microscope, an achromatic object-glass, of nine-tenths of one inch focal length, composed of three lenses, and transmitting a pencil of eighteen degrees. This was the first achromatic microscope that had been made in England.
By the labours of these practical opticians, and the suggestions of various scientific persons, as Sir John Herschel, Mr Airy, Mr Barlow, one great defect of the compound microscope was obviated. There was still another under which the instrument laboured; the effects of spherical aberration. This was overcome, in a very simple manner, by the experiments of Mr Jackson Lister, who had early observed that the combined achromatic object-glasses, devised by Selligues, were fixed in their cells with the convex side foremost, and that this is the most improper position, as it renders the spherical error very great. This gentleman found, after various trials, that, by placing three or more achromatic glasses with their plane surfaces directed foremost, it was possible to correct completely all spherical aberration.
This fact was made known in the beginning of the year 1830; and by its application, the compound microscope was brought to a high degree of perfection as an achromatic instrument in 1831 and 1832, and became the means of affording valuable assistance in anatomical inquiries. After this period, accordingly, we find a succession of valuable monographical essays appearing, from time to time, from the anatomists of this country and the continent, on the minute microscopical anatomy of various important organs of the animal body. The whole of these writings it is impossible to mention in this place, further than to say that the use of the microscope in anatomy, which had in the times of Malpighi, Leeuwenhoek, William Cowper, Baker, Fontana, Hewson, and the second Monro, been much cultivated, but had afterwards, from the imperfection of the instrument, and the illusions to which it not unfrequently gave rise, been unduly neglected, became so general and so necessary, that it may be said that, since the year 1832, minute structural anatomy has been, if not created anew, at least most thoroughly revised. The amount of knowledge has been increased; that which was already possessed was rendered greatly more accurate and precise.
By the aid furnished by these improved instruments, John Muller was enabled in 1830 to publish his elaborate Commentary on the Minute Structure of the Glands, the first work in which the anatomy of these organs was examined and elucidated in a comprehensive and systematic manner. By the aid of the same instrument Ehrenberg was enabled
---
1 On some Properties in Achromatic Object-Glasses applicable to the Improvement of the Microscope. By Joseph Jackson Lister, Esq. Philosophical Transactions, 1830. Read 21st January 1830. History. to publish, in 1833, his observations on the Minute Structure of the Brain; to explain in a manner hitherto impracticable the structure of numerous infusoria, and to disclose the peculiarities of many other structures, animal, vegetable, and mineral, which had previously eluded the most skilful researches. By the same means Francis Kiernan, in 1833, published the first correct account of the Minute Anatomy of the Liver. By means of the same assistance, Dr Martin Barry has communicated a large amount of new and correct information upon the structure of the Germinal Vesicle and the changes which it undergoes; the structure of cells; the minute structure of muscular fibres, and several other subjects intricate and little understood. By the same means, Mr William Addison and Mr George Rainey in this country, and M. Rossigpol in Belgium, have been enabled to investigate carefully the minute structure of the lungs, and the disposition and figure of the air-vesicles. By the same means Gulliver, Quackett, and Wharton Jones, have studied to explain the minute structure of the corpuscles or globules of the blood in different classes of animals, and have thrown much light upon the forms of these globules. Lastly, by means of the same instrument, Mr Bowman has been enabled to give the first clear and intelligible views of the sacculo-vascular structure of the corpora globosa or Malpighian bodies of the kidney, and has shown in what manner the cirriform or curling capillaries of these bodies contribute to the secretion of the urine; while in the same department Huschke, Reichert, Gerlach, and Bidder, have laboured with great perseverance in elucidating various obscure points.
For several years past, in short, anatomists in Great Britain, France, Switzerland, Germany, Belgium, and Holland, have been industriously occupied in studying various departments of minute anatomy, by means of the improved compound microscope, and in throwing light upon all those points that are most obscure and uncertain. It cannot be said, nevertheless, that all has been discovery and all acquisition. These investigations have given rise to a large proportion of discordance in the representations given by different observers; and though all must have beheld the same objects, yet all have not put upon them the same interpretation. The result is, that it is a work of no ordinary difficulty to reconcile these discordant points, and out of the whole stock of facts, to form a consistent and correct description. Perhaps a considerable time must elapse before all these difficulties can be fully explained, and all the points of discordance can be satisfactorily reconciled.
Meanwhile, it is proper to mention that systematic treatises have shared in the general improvements and rectifications thus introduced into anatomical science. In the year 1833 Carl Frederick Theodore Krause published at Hanover the first division or section of the first volume, in the year 1836 the second part, and in 1838 the third division, completing the first volume of a Handbook or Manual on Anatomy, General and Special. The general anatomy is given in the first part of the first division; the rest of the first division is occupied with the anatomy of the skeleton, the muscles, the ligaments, and the fasciae. The second division is employed in explaining the anatomy of the compound organs and apparatus, including the organs of the senses, those of respiration, digestion, the organs of secretion, and those of reproduction. In the third division the author treats of the heart, the bloodvessels and lymphatics, and the nervous system.
This treatise is one of great merit. It is remarkable for clearness and method, brevity, accuracy, and precision; and the author must be allowed to have presented a most instructive system of anatomical knowledge. Krause has given in it accurate average estimates of the weights and dimensions of the different organs. This work appeared in a second edition in 1841 and 1842.
In the year 1837, Joseph Berres, professor of anatomy at Vienna, published in that city the Microscopical Anatomy of the Human Body; and in which he gave views of the anatomy of all the simple textures and the various organs, as disclosed by the microscope. The instrument which Professor Berres employed was one made by Ploesslich. This work is undoubtedly one of great labour and no ordinary value; but probably it is in its plan too comprehensive, and embraces too large a field to be in all points accurate. The descriptions are given in the German and Latin languages.
Crucellier published in 1834 and 1835, a good general treatise on Descriptive Anatomy, which was translated into English, and published in 1841 as part of the Library of Medicine. A new and improved edition of this treatise the author himself published at Paris in 1842 and 1844.
The excellent work by Samuel Thomas Soemmerring, originally published in the German language, between the years 1791 and 1796; then in the Latin language between the years 1794 and 1800; and in a second edition in the German language in 1800 and 1801, maintaining the high character which it first possessed for clear arrangement, accurate description, and general precision; was between the years 1841 and 1844 republished in eight volumes at Leipzig, by Bischoff, Henle, Huschke, Theile, Valentin, Vogel, and Wagner, with suitable additions, and a large amount of new and accurate information. In this edition Rudolph Wagner gives in the first division of the first volume, the Life, Correspondence, and Literary writings of Soemmerring; and, in the second volume, the anatomy of the Bones and Ligaments. The third volume contains the anatomy of the Muscles and the Vascular system by Theile. Valentin devotes one volume, the fourth, to the minute anatomy of the Nervous system and its parts, as disclosed by careful examination by the microscope; and it must be allowed that the author has been at great pains to present just views of the true anatomy of the Brain, the Spinal Cord, the Nervous Branches, and the Ganglia. In the fifth volume, Huschke of Jena, gives the anatomical history of the Viscera, and the organs of the senses; a department which had been left in some degree incomplete in the original; but for one division of which the author had left useful materials in his large figures already mentioned. In the sixth volume, an entire and complete system of General Anatomy, deduced from personal observation; and that of other careful observers, the materials being in general new,
---
1 Handbuch der Menschlichen Anatomie Durchaus nach Eigeneren Untersuchungen und mit Besonderer Rücksicht auf das Bedürfniss der Studirenden der Praktischen Aerzte und Wundärzte und der Gerichtsärzte Verfasst von Carl Friedrich Theod. Krause, M.D., U.S.W. Erster Band In Drei Abtheilungen. Hannover 1833-1838.
2 Anatomische Mittheilungen Gebilde des Menschlichen Körpers. Von Dr Joseph Berres K. K. Öffentliche Professor der Anatomie an der Wiener Universität, &c. Wien 1837, Folio.
3 Anatomia Microscopica Corporis Humani. Auctore Dr Josepho Berres Professore Publico Ordinario in Universitate Vindobonensi, &c. Viennae 1837, Folio, p. 272, with numerous plates.
4 Descriptive Anatomy. By T. Cruveilhier, Professor of Anatomy to the Faculty of Medicine of Paris, Physician to the Hospital of Salpetriere, &c. Two volumes small 8vo, London, 1841-42, pp. 1214. Library of Medicine, volumes seventh and eighth.
5 Samuel Thomas Von Soemmerring vom Bane des Menschlichen Körpers. Neue umgearbeitete und vervollständigte Original Ausgabe Besorgt von W. Th. Bischoff, J. Henle, G. Huschke, F. W. Theile, G. Valentin, J. Vogel und Rud. Wagner. Leipzig 1841-44. Acht Bände.
VOL. II. History, and in all instances confirmed and rectified, is given by Henle, at that time at Zurich, but subsequently professor at Heidelberg. The seventh volume contains the history of the process of Development in Mammalia and Man, by Th. L. W. Bischoff. The eighth volume contains the Pathological Anatomy of the Human Body, by Julius Vogel, but only the first division thereof, relating to the generalities of the subject.
This, which is probably the most accurate, as it is the most elaborate system of anatomical knowledge up to the date of its publication in 1844, was translated into the French language by Jourdan, and published in 1846, under the name of Encyclopedie Anatomique. The eighth volume was translated into the English language in the year 1847.
In 1840, Francis Gerber published at Berne a Manual of General Anatomy in the Human Subject and the Domestic Mammalia. Of this work, which contains a large amount of new and accurate information, an English translation was published by Mr Gulliver in 1842.
In 1846, Joseph Hyrtl published at Prague a system of Anatomy of the Human Body in reference to Physiology, which contains short but interesting views of the Physiological Anatomy of the different organs. In the course of the same year, and in 1847, the same writer published a Manual of Topographical and Surgical Anatomy; the latter chiefly for surgeons and accoucheurs, as the former work was intended for the benefit of physicians. The second volume contains the surgical anatomy of the Male and Female Pelvis, the Spine, and the extremities.
Bourgy began in 1834 to publish a work on Elementary Anatomy; and in 1837 a large and complete system of anatomical knowledge, illustrated with large figures of all the divisions and organs of the human body. This work consist of two divisions, one on Medical and Physiological Anatomy; the other on Surgical Anatomy. It is only now completed.
In England the treatise by Jones Quain, which was highly esteemed, was republished in a fifth edition between the years 1843 and 1848, by Mr Richard Quain and Dr Sharpey, in two volumes. The work was in this form enlarged to about double its previous size; and it contains a large amount of accurate information in General Anatomy, and in several of the divisions of Descriptive Anatomy. The General Anatomy is written entirely anew by Dr Sharpey, who has taken great pains to present a just and accurate view of the state of knowledge in that department. This work is the most complete English system hitherto published. Of various English manuals, those by Ellis, by Wilson, and Harrison, are most entitled to recommendation.
In the three years between 1846 and 1849, Dr Arthur Hill Hassall published the Microscopic Anatomy of the Human Body in Health and Disease. Though in this work the author treats of the morbid state of the fluids and solids, as well as their normal or healthy condition; yet as he takes great pains to give correct views of the minute anatomy of the textures in the state of health, it would be unjust here to omit mentioning his services. The work is illustrated by sixty-nine coloured drawings, and may be recommended as one giving very just views of the minute anatomy of the tissues and organs, both from personal observations, and that of contemporary inquirers.
In the year 1850, Dr A. Kolliker, Professor of Anatomy at Wurzburg, published at Leipzig the first half of the second volume of a work devoted to the elucidation of the microscopical anatomy of the human body; and in 1852 the second half of the same volume. For manifold reasons the author states that he publishes the second volume, which is devoted to the history of the Special or Particular Tissues, before the first. In the first half of this volume, Kolliker treats of the microscopical anatomy of the Skin, the Muscles, the Bones, and the Nerves, and in the first division of the second half of the microscopical anatomy of the Organs of Respiration and Digestion. From the specimens already published, this work gives the promise of being the most complete and accurate hitherto published on the subject of minute structural anatomy. The author has been at great pains in examining every texture with the greatest care, and comparing his own observations with those given by previous and contemporary anatomists; and while the information is ample on every disputed point, every reader must feel that he finds in this work more accurate knowledge on the intimate structure of organs than he had previously possessed. This work, when completed, will, in short, probably prove to be the standard treatise on general and microscopical anatomy. The descriptions are illustrated by numerous beautiful wood engravings (295), and four lithographed tables.
The account now given embraces the principal works upon anatomy, not by any means the whole, that have been published since the use of the improved compound microscope has become general. Many writings of very considerable merit upon individual subjects and questions in anatomy have during the same time appeared in different countries of Europe. Upon the brain and the nervous system they have been most numerous; some inquirers devoting their attention to the nerves, as Remak, Purkinje, Pappenheim, Bidder, and Volkmann, Budge, Schiff, Bowman; others, as Valentin, Longet, Solly, Todd, Lockhart, to the Brain and its Vertebral Prolongation. These, however, the limits assigned to the present outline prevent us from recording. It shall be our study, nevertheless, in the proper place to notice whatever facts may seem most important, as ascertained by each, as far as the nature and objects of this article will admit. Minute details it will not be possible to introduce. But it shall be our endeavour to present upon the structure of the tissues and the different organs, such accounts as may convey a just idea of the facts hitherto ascertained, and may enable readers to form correct notions on the state of anatomical knowledge in the middle of the nineteenth century.
---
1 Fr. Gerber Handbuch der Allgemeine Anatomie des Menschen und der Haussäugthiere mit Steindruck Tafeln. Folio. 2 Durchgesch. Ausgabe gr. 8vo. Bern, 1840. 2 Elements of General and Minute Anatomy by Fr. Gerber, translated by George Gulliver. London 1842, atlas 8vo. 3 Joseph Hyrtl Lehrbuch Anatomie des Menschen mit Rücksicht auf Physiologische Begründe und Praktische Anwendung gr. 8vo. Prag, 1846. 4 Joseph Hyrtl Handbuch der Topographischen Anatomie und ihre Praktische Med-Chirurg Anwendung mit Steindruck Tafeln N. Einer Band gr. 8vo. Wien 1846-47. 5 Elements of Anatomy by Jones Quain, M.D., Fifth Edition. Edited by Richard Quain, F.R.S., and William Sharpey, M.D., F.R.S., Professors of Anatomy and Physiology in University College, London. In two volumes, Illustrated with numerous engravings in wood, 8vo. General Anatomy, ccxvii. pp.; Descriptive Anatomy, cccxxiv pp. 6 The Microscopic Anatomy of the Human Body in Health and Disease. Illustrated with numerous Drawings in colour, by Arthur Hill Hassall, M.B., &c., Member of the Royal College of Surgeons, England. In two volumes. London 1846-9; 8vo, pp. 570. Sixty-nine coloured Drawings. 7 Mikroskopische Anatomie; oder Gewebelehre des Menschen von Dr A. Kolliker, Professor der Anatomie und Physiologie in Wurzburg. Zweiter Band Specielle Gewebelehre; Erste Hälfte mit 168 Holzschnitten. Leipzig 1850, größe 8vo, seite 554, Zweite Hälfte I. Abtheilung Mit 127 Holzschnitten. Leipzig 1852, seite 346. In the foregoing account we have been anxious to trace merely a general sketch of the progressive advancement of anatomical discovery, from the first cultivation of the art to the present time. To mention every circumstance is impracticable, and would have extended this outline much beyond its legitimate limits. Though no name of genuine importance, however, has been omitted, every one not directly connected with strict anatomy has been excluded.
For more minute and detailed information, we refer in general to the elaborate History of Anatomy and Surgery by Portal, the Bibliotheca Anatomica of Haller, and the critical and learned history of Lauth. The latter work is not completed. But by combining its perusal with that of the works already mentioned, and several of the chapters of Sprengel's History of Medicine, the anatomical inquirer will form very just ideas of the literary history of his science.
HUMAN ANATOMY.
All animal bodies agree in the possession of certain general characters, by which they are distinguished equally from inorganic bodies and from vegetables.
Besides the round shape by which organic bodies are distinguished, most animals are, externally at least, symmetrical, or present on each side of the mesial plane, lateral halves mutually alike. The substances of which they consist are not entirely solid, but are soft, compressible, distensible, and elastic, and contain a proportion of liquid matter, which is generally in the ratio of majority to that of the solid. These substances are enveloped in a thready or filamentous matter, named areolar or cellular, from the interstitial spaces which result from the intersection of its filaments; and the whole is inclosed in a general covering, which in several classes is soft, membranous, and elastic, but in others is hard, crustaceous, and even horny. The body is perforated by an internal cavity for the reception of food; and this cavity is lined by a membranous covering, which is continuous with that by which the exterior is involved. In several classes of animals there are tubular canals, distributed in an arborescent form, for conveying, in definite directions, the nutritious matter to all parts of the frame. These are named blood-vessels, or organs of circulation. One modification of these, arranged in such manner that this matter is subjected to the influence of the atmospheric air, forms lungs, gills, or organs of respiration; and another, in which part of it is separated from the whole, constitutes secreting organs or glands. The genital or reproductive organs consist of a cavity, from which the germs or ova are detached. For the purpose of motion, animals further possess organs generally of a fibrous structure, and which have the remarkable property of undergoing contraction on the application of a stimulus or irritating agent. These organs are denominated muscles (lacerti, tori); and their contractile property is termed irritability or contractility. For receiving the impression of external objects, they are provided with one or more organs of sensation, of structure more or less complex. And in almost all animal bodies, except the very lowest, there are found soft, gray, or whitish cords, inelastic, but marked in their course by fusiform, spheroidal, or irregular-shaped swellings, and connected at their further extremity with the muscles, with the organs of sensation, or with the exterior or interior coverings. It is remarkable that the purpose of these cords, which are named nerves, is not exactly known. They neither communicate mobility to the muscles, nor sensibility to the organs of sensation; but they render the actions of the former steady, regular, and voluntary; and the impressions received by the latter they certainly serve to convey to the centre of the nervous system.
The faculty ascribed to the nerves is named nervous action, nervous energy, nervous power, nervous influence, or simply innervation.
In chemical composition, animal bodies consist of gelatine, albumen, fibrin, fat or oleaginous matter, a modification of mucus, and various saline substances. Subjected to combustion, or spontaneous decomposition, while vegetable substances furnish water, carbonic acid, and carburetted hydrogen, animal matters furnish also ammonia,—a circumstance which shows that they contain azote. They furnish also sulphuretted hydrogen, apparently from the decomposition of albuminous matters.
The fluids of animal bodies (liquores, latices, humores) are contained in tubular canals or vessels. If these fluids move through the vessels, they are denominated, generally blood, whatever be their colour. All the fluids consist either of this, or of some modification separated from it by means of glandular action; and of the fluids so separated, some are destined for purposes within the economy, and are therefore secretions proper; others are intended to be eliminated immediately, and may therefore be regarded as excretions. Though it is impossible to estimate accurately the proportion of the fluids, some idea of it may be formed by the fact, that an animal body may be reduced by desiccation to $\frac{1}{9}$ or $\frac{1}{10}$ even of its previous weight. The proportion may be stated, in general terms, to vary from 9 or 6 of fluid, to 1 of solid matter.
The various forms of animal bodies may be referred to general divisions or classes, according to certain peculiarities in configuration and structure. These divisions are, the Vertebrata, Mollusca, Articulata, and Radiata.
In the first class the central portion of the nervous system, consisting of the brain and spinal chord, is inclosed in a case of hard matter, containing much calcareous earth, and denominated bone. While one portion of this forms, by the union of its pieces, a cavity named the skull or cranium, the other is composed of separate pieces, which by their union constitute at once a continuous canal and a sort of internal pillar or column for attaching and supporting the soft parts. These pieces are named vertebrae (στεφάναι); and their presence is so uniform, that they constitute the character of the class, which are therefore named Vertebrated Animals; (Animalia Vertebritis predita, sive Vertebrata).
The presence of vertebrae is accompanied with other peculiarities of structure. Thus the vertebrated animals have red blood and a muscular heart; a system of tubes for conveying blood from this to the different organs,—the distributory, or arteries; another system for returning it,—the regredient, or veins; and a particular system of vessels for exposing the latter blood to the influence of the atmosphere. They have further a mouth with two horizontal jaws; distinct organs of vision, hearing, smell, and taste, lodged in the cavities of the face; never more than four members; separate sexual organs; and considerable similarity in the arrangement of the central masses and the ramified chords of the nervous system.
In all the vertebrated animals the blood which serves for the secretion of bile is the venous, which has circulated in the intestines, and which is afterwards made to undergo a ramifying distribution in the portal vein. In all the vertebrated animals also a peculiar secretion is formed from the arterial blood by two large glands, denominated kidneys.
In the second general division, which are destitute of those firm pieces named bones, the central portion of the nervous system, instead of being inclosed in portions of the skeleton, is placed on the oesophagus, and, with the other internal organs, is inclosed in a general soft envelope, contractile, corresponding to the skin, to which the muscles are attached, and in which stony patches named shells are occasionally formed. Of the four proper organs of sensation, those only of taste and sight are observed; and the last are often wanting. One family only are provided with organs of hearing. There is always a complete system of circulation, and organs for respiration. Those of digestion and secretion are almost as complicated as in the vertebrated animals. The division of the animal world thus distinguished have been named MOLLUSCOUS ANIMALS (Animalia Mollusca).
In the third general division, the nervous system consists of two chords extending longitudinally along the belly, and swelling at intervals into knots or ganglions. The first of these, placed on the oesophagus, and distinguished as the brain, is scarcely larger than the others. The covering of the trunk is divided by transverse folds into a number of rings, the integuments of which may be hard or soft, but to the interior of which muscles are in all cases attached. The sides of the trunk, though often provided with, are nevertheless often without, articulated members. The annular appearance of the trunk has given these animals the character of ARTICULATED (Animalia Articulata). They have been occasionally named ANNULOSA.
This class of animal bodies is remarkable for presenting the first transition from circulation in close tubes or vessels, to nutrition by imbibition, and the corresponding transition from respiration in circumscribed organs to that which takes place in air-tubes distributed through the whole body. The only distinct organs of sensation are those of taste and sight; and a single family have organs of hearing. The jaws, when present, are lateral.
In these three divisions of animals the organs of motion and sensation are arranged symmetrically on both sides of an axis or imaginary line. In a fourth class they are distributed circularly round a centre. In these, which in homogeneous structure approach the nature of plants, neither distinct nervous system nor proper organs of sensation are observed. Scarcely do we recognise traces of circulation. The organs for respiration are almost always at the surface of the body. Most of them have for intestine a sac without vent; and some present only a homogeneous pulp, movable and sensible. To this class, which comprehends those beings denominated since the time of Aristotle zoophytes (ζωοφύτα), or animal plants, the name of RADIATED ANIMALS has been recently applied (Animalia Radiata).
The vertebrated animals, however similar in general characters, present certain peculiarities by which they are naturally distinguished into classes. The first, and perhaps the most striking difference, is in the mode of birth, one large division being separated from the body of the female parent in a state of complete life, and therefore denominated viviparous; the other being detached in the form of an ovum or egg, which, though possessed of the elements of life, is not yet endowed with it, and requires for the full development of that principle the assiduous care of the parent. This difference, however obvious, is more apparent than real. In viviparous birth the fetus or new animal remains attached to the inner surface of the womb by means of nutritive blood-vessels, and is enveloped in membranes, which correspond very accurately to the coverings of the egg of oviparous animals. The rupture of these membranes at the moment of birth or detachment from the body of the parent is the only circumstance which constitutes a material difference between viviparous and oviparous generation. The viviparous animals, nevertheless, are further distinguished by nursing their offspring by means of teats or mammas, glands destined for separating from the mass of blood the oleo-albuminous fluid denominated milk.
A still more important source of distinction among the vertebrated animals is found in the disposition of the vascular organs destined for respiration. The blood, which proceeds from the heart by the distributing tubes or arteries to the different organs, thereby undergoes a certain change, in consequence of which it is no longer capable of answering the several purposes of nutrition, secretion, &c., which are necessary to the maintenance of the animal body in the healthy state. To fit it once more for these purposes, the blood, in whole or in part, is, by means of the veins, brought back to the heart, and thence conveyed by means of a system of arborescent tubes to the surface of an organ, where it is, through the interposition of a thin membrane, exposed more or less freely to the atmospheric air. When it is exposed directly to this fluid introduced into the body by means of a single tube divided into ramifying branches, the respiratory organ is denominated lungs. When the blood, on the other hand, is exposed to atmospheric air by means of water, which passes over a pectiniform organ, the latter is denominated gills. Respiration varies, therefore, according as the structure of the organ allows the whole or part of the blood to be exposed to air, and according as this exposure is direct or indirect.
Taken together, these circumstances may be viewed as the integrant or constituent elements of the quantity, extent, or degree of respiration, which conversely, indeed, depends on two circumstances,—the quantity of blood present in the respiratory organ at any given moment, and the relative quantity of oxygen in the respired fluid.
The organs of circulation may be double, so that the whole mass of blood which is brought by the veins from the remote parts must circulate in the respiratory organ before it is again distributed by the arteries;—or they may be single, so that one portion only of the regredient blood is made to pass through the respiratory organ, while the residue is distributed by the arteries without undergoing this circulation. Of this mode of respiration an example is given by the class of animals denominated Reptiles (Reptilia; Animalia Repentia); in which the heart is so constructed that only part of the blood is conveyed to the lungs, and in which, consequently, the amount or degree of respiration, and the concomitant qualities, vary according to the proportion of this fluid which goes to the lungs at each pulsation.
In Fishes, on the other hand, though the circulation is two-fold, that is, distributory by means of arteries, and regredient by means of veins, the respiratory organ is formed for respiration through the medium of water, and the blood thus exposed to air receives the influence of that only which is mingled or held in solution by the water. Their extent of respiration is therefore supposed to be less than that of reptiles, by reason of the imperfect exposure to the operation of the air. Their respiration may be termed hydro-aerial.
In mammiferous animals, again, though the circulation is two-fold, or distributory and regredient, the respiration is single, or confined to the lungs only. Their extent of respiration is therefore superior to that of the reptiles, by reason of the shape of their circulatory organs, and to that of fishes by reason of the nature of the element in which they live. Their respiration is aerial.
In another class of vertebrated animals, however, respiration assumes a form still more perfect and extensive, since not only is the circulation two-fold, and the respiration aerial, as in the mammalia, but their structure is such that the air of the trachea communicates with other cavities, especially those of the bones, and surrounds the branches of the aorta as completely as it does those of the pulmonary artery. The effect of this arrangement with regard to the ambient atmosphere is at once to render these animals specifically lighter, and enable them to support themselves in the air, and to restore and change the regredient or venous blood so completely, that when again distributed it may impart to the various organs the highest degree of energy of which they are susceptible.
From these characters a division of vertebrated animals may be formed in the following manner. 1st, Quadrupeds, in which the extent of respiration is moderate, and which are distinguished for walking or running, or other muscular exertion with strength; 2d, Birds, in which the extent of respiration is the greatest possible, and is connected with the levity of substance and energy of muscle requisite for flight; 3d, Reptiles, in which the small extent of respiration is connected with languor of motion and occasional seasons of torpor; and, 4th, Fishes, in which the still more limited form of the respiratory organ requires a fluid of nearly equal specific weight to their own bodies to enable them to move with facility. These characters are necessarily general; but they are so essential, that between them and the other circumstances of organization proper to each class, and especially those relating to motion and sensation, a necessary relation exists.
To the quadrupeds, mammiferous animals, or viviparous vertebrated animals, which form the first of these great classes, this place belongs, not only by the mode of generation and respiration, but by the more perfect form of the animal functions, and the higher degree of intelligence which their habits and actions indicate. They are less under the influence of that blind animal propensity denominated instinct, which, like the properties of inorganic matter, seems to operate regularly and uniformly, independent either of sensation or volition.
This class of animals is distinguished by great uniformity and regularity of structure and organization. In all of them the upper jaw forms part of the cranium; and upon this the lower jaw, consisting of two pieces only, articulated by a prominent condyle to the temporal bone, is made to move. The neck consists of seven, and, in one species only, of nine vertebrae; to the sternum are attached certain of the ribs, therefore named sterno-vertebral; the thoracic extremity is supported by a flat bone named shoulderblade (scapula, ωστραχνη), not articulated, but simply suspended in the muscles, and in some species supported on the sternum by an intermediate bone, named collar-bone or clavicle (clavícula, κλαυκή); in all excepting the cetacea or whale-like animals, the first part of the pectoral extremity is fixed to the vertebral column, and forms a cincture or basin (pelvis), which in early life is divided into three pairs of bones, the os ilium, which is attached to the spine, the os pubis, which constitutes the anterior or abdominal part of the pelvis, and the os ischium, which constitutes the most remote lateral portions of the pelvis. At the point of junction of these three bones on each side is a spherical cavity, in which the articular head of the thigh-bone is lodged.
The skull, articulated by two prominent convex surfaces with the first vertebra, denominated atlas, may be represented as consisting of three annular portions, an anterior formed by the frontal and ethmoid bones, a middle by the parietal and sphenoid bones, and a posterior by the occipital bone; the temporal bones, which are common to the face and skull, being interposed between the sphenoid, the occipital, and the parietal bones.
The face is formed essentially by the superior and inferior maxillary bones. Between the former is the cavity of the nostrils above, separated by the zygomatic bone named vomer; before are the intermaxillary bones, and behind are the two palate bones. The entrance of the nasal cavity is bounded above by the proper nasal bones; and to a groove in this cavity are attached the inferior turbinated bones, so as to cover partially the entrance into the maxillary sinus.
The brain consists of two similar hemispherical halves, united by a white mass, fibrous, especially in the transverse direction, named mesolobe, middle-band, or smooth body (σύμη τοξόβολος, corpus callosum). Each hemisphere contains an interior cavity, formed into definite-shaped masses, uniform and symmetrical. These cavities communicate with each other, and with a third situate on the mesial plane, and extending by a narrow canal to a fourth situate between the cerebellum and medulla oblongata. The proper matter of the cerebral and cerebellar hemispheres is united on the mesial plane in a mass named annular protuberance or pons Varolii, the lower surface of which is marked by transverse fibres, while the upper is moulded into four roundish eminences named nodus and testes, or corpora quadrigemina.
In the eye, lodged in a cavity of the cranium named orbit, and provided with two eye-lids and the vestige of a third, the crystalline lens is fixed by the ciliary processes; and the sclerotic, though firm, is cellular. The ear consists of a cavity named tympanum, closed externally by a membrane, and containing four minute but articulated and movable bones; an oval cavity or vestibule, in the orifice of which, one of these bones, the stapes, is fixed, and which communicates with three semi-circular canals; and, lastly, a spiral and tapering cavity, termed cochlea, parted by a thin plate into two spiral canals, one of which communicates with the tympanum, the other with the vestibule. The tongue is fleshy, and is supported by a parabola-shaped bone, attached to the cranium by ligaments, and to the larynx by membranes.
The lungs, in number two, consisting of numerous tubular canals, proceeding from the windpipe, and terminating in an infinity of minute intersecting canals, named cells or vesicles, are inclosed without attachment, in a cavity formed by the ribs on each side, the diaphragm abdominally, and on the mesial plane by a membranous partition named mediastinum, and lined all over by a thin transparent membrane (pleura). At the guttural extremity of the windpipe is placed a particular apparatus, formed of cartilages put in motion by muscles, and which serves at once to regulate the quantity of air admitted into the tube, and to form the voice. This is named the Human larynx. A membranous fleshy production, suspended from the palate bones like a veil or valve, also moved at the will of the animal, establishes a direct communication between the larynx and the posterior nostrils.
The intestinal canal is suspended to a duplicature of the peritoneum, named mesentery, between the folds of which the blood-vessels, nerves, lymphatics, and lymphatic glands pertaining to the canal, are lodged. The peritoneum, after passing over the intestines, forms a similar duplicature, which in the manner of a prolongation hangs freely before them.
The urine, after secretion by the kidneys, is retained for a time shorter or longer in a distensible musculo-membranous bladder, and is expelled at various periods by a canal which opens, with few exceptions, in common with that of the organs of generation.
The latter function is, in all the mammiferous animals, essentially viviparous. The ovum, consisting of the fetus and the enveloping membranes, immediately after conception is conveyed by appropriate tubes into the womb, to the inner surface of which it is attached by one or more plexiform clusters of vessels named placenta, and which furnish the blood requisite to the nourishment of the new body. In the earliest periods of uterine life, however, the mammiferous animals present a bladder or vesicula (vitellar membrane), analogous to that which contains the yolk of the oviparous animals, and receiving also mesenteric vessels.
The peculiar mode in which viviparous animals nurse their offspring has been already noticed as that which distinguishes them particularly from the other three divisions of vertebrated animals.
Another character peculiar to this class, are the hairs with which their integuments are provided, and which, though analogous to the feathers or quills of birds, are nevertheless so characteristic, that they cannot be properly omitted in this enumeration. They are found in all mammiferous animals except the cetacea, in which marine residence is supposed to render them less necessary. Lastly, the blood of the mammalia is said to differ from that of oviparous animals in the shape of the coloured particles. In the former they are represented as lenticular, or of the shape of flat or oblate spheroids; in the latter they are ovoidal, or like oblong spheroids.
The mammiferous animals may be subdivided into subordinate groups or orders, according to certain natural characters in organization, which imply again peculiarities of habit and mode of life. These characters are derived from the organs of touch or prehension, on which depends their degree of ability or address; and from the organs of mastication, which always bear a certain relation to the nature of the food on which the individual animal subsists.
The delicacy of the organ of touch depends on the number and mobility of the toes, and on the extent to which their tips are enveloped in nail or hoof. The latter, enveloping entirely the part of the foot which touches the ground, impairs sensation, and renders the foot or paw incapable of prehension. When, on the contrary, a single plate of nail covers one of the surfaces of the tip of the toe, it not only leaves the other all its natural nicety of touch, but gives each toe that free and unembarrassed motion which enables the animal to seize and hold by the claws.
The nature of the aliment used by animals bears a relation to the teeth, with the form of which, again, the articulation of the jaws corresponds. To divide flesh, incisive teeth, like a saw, and jaws mutually opposed, like the blades of scissors, which simply open and shut, are requisite. In order to break grains or roots, teeth with a flat crown, and jaws admitting of horizontal motion, are required. The crowns of these teeth must further be unequal or tuberculated, like the surface of a mill-stone, and their substance must be unequally firm, since certain parts are more exposed to attrition than others.
All hoofed animals are necessarily herbivorous, or have flat-crowned teeth, since their feet do not allow them to seize living prey. Unguiculated animals, again, are susceptible of greater variety in the shape of the teeth, and their aliment depends on the mobility and delicacy of their toes. One character of this description, which exercises great influence on their address, and multiplies their means of industry, is the faculty of opposing the great toe to the others, or the thumb to the fingers,—a circumstance which essentially constitutes what is termed the hand, and which is carried to its highest perfection in the case of man, in whom the pectoral extremity is entirely free and susceptible of every mode of prehension.
The several combinations now mentioned furnish characters for distinguishing the mammalia into the following orders.
**Bimana**: hands on the thoracic extremity; supported vertically by the pelvic extremities.
**Quadrumania**: hands on the thoracic and pelvic extremities.
**Carnivora**: toes without free and opposable thumb.
**Rodentia**: no canine teeth; gnawing incisors.
**Edentata**: occasionally no canine; sometimes teeth wanting.
**Marsupialia**.
**Pachydermata**: dense, compact, callosus hide.
**Solidipeda**: six incisors and six molars in each jaw; single stomach and large cecum; one undivided hoof.
**Fissipedia & Ruminantia**: no incisors in the upper jaw; quadruple stomach; cloven foot.
**C. Herbivora**.
**C. Capitulata**.
**C. Capitones**.
Of these subdivisions, the first three orders are known by the common character of possessing all the three varieties of teeth, molar, canine, and incisive. They differ from each other in the possession of complete hands on the thoracic extremities, of imperfect hands on the four extremities, and in the want of thumb or opposable toe on the four extremities. The fourth order is peculiar in wanting canine teeth, and having incisors constructed for gnawing. In the fifth the toes are much constrained in motion, being sunk in large claws; and the incisors are wanting. Some genera want the canine teeth, and some are void of teeth entirely.
This distribution of ungualculated animals would be complete, and would form a regular series, were it not interrupted by a small lateral series from New Holland, the native soil of the Marsupial animals. Of these, it is the peculiar distinction, that while some of their genera correspond to the Carnivora, others to the Rodentia, and a third set to the Edentata, in the form of teeth and na- In the series of hoofed animals, which are less numerous, less irregularity is also observed. The order of Ruminant animals is well distinguished by cloven feet, the absence of incisors in the upper jaw, and the quadruple stomach, or that with four compartments. The other hoofed quadrupeds may be united in one order, distinguished by the absence of the ruminating stomach, and a peculiar density of integuments, from which they are named Pachydermata. The elephant alone constitutes a distinct family, and is allied, by the form and mechanism of the teeth, with the family of Rodentia. A third family of hoofed quadrupeds is distinguished by one apparent toe and one hoof in each foot; though beneath the skin, on each side of the metacarpus and metatarsus, are prominences corresponding to lateral toes. This small family (Solidipeda) includes the horse, ass, zebra, and quagga.
Lastly, the Cetaceous or whale-like animals form a family by themselves, so peculiar, that though viviparous and mammiferous, they might readily be regarded as belonging to the class of fishes. Their organization, however, immediately shows their proper place in the classification; and even the fact observed by the ancients, that, though pisciform, they have warm blood, demonstrates their title to the character of Mammalia.
Man, who, as the most perfect specimen of mammiferous animal with which we are acquainted, is placed at the head of this class, partakes of the general characters of structure and function belonging to the class, and possesses also certain peculiarities by which he is distinguished. The study of the facts of the former description belongs properly to Comparative or Animal Anatomy. That of the latter constitutes Human Anatomy proper. It is, however, expedient to waive this distinction, and trace the anatomical history of the human body, without supposing the reader already minutely acquainted with the structure of mammiferous animals in general. In the course of this description, however, it is requisite to recur frequently to the lower animals, and to derive from them information more or less direct, tending to illustrate the structure of the human subject.
The external appearance of the human frame it is superfluous to describe minutely. Naturalists distinguish man as a bimanual and biped animal, or as one possessing two complete hands, and supporting himself in the vertical position by the two pelvic extremities. These characters are neither arbitrary nor unessential. Both depend on invariable peculiarities of structure; and whatever attempts have been made by men, more distinguished for ingenious paradox than accurate observation, to show that man was naturally quadruped, are readily refuted by appealing to the anatomical configuration and disposition of the four members, and their relation to the trunk.
Another character of the human subject is the globular or rather spheroidal shape of the skull, and its large size in proportion to the rest of the frame, with the general tendency of the plane of the face to the vertical direction. In no other mammiferous animal does the head make so near an approach to the spheroidal shape; and in no other is the plane of the face so nearly vertical. In the other Mammalia, the skull is angular-oblong, and the face acquires a peculiar character, which is readily ascribed to the lower animals by the extreme projection of the mouth, or, in other words, by the length to which the two jaws are prolonged. Even in the monkey tribe, the similitude of which to the human face was remarked by the poet Ennius, this remarkable character is by no means lost; and the upper and lower jaws make a much more conspicuous projection than in the human skull.
The great characteristic of the human race, however, is articulate or oral speech, which, combined with the perfect development of which the mental faculties are susceptible, constitutes a very wide distinction between man and the lower animals. The latter possess what may be termed laryngeal voice, or that which is formed in the larynx. To man is superadded the faculty of articulate speech by means of the lips, tongue, and teeth.
All the known individuals of the human species, though agreeing in the possession of the general characters now enumerated, and therefore to be regarded as unigenious, or of one general family, differ nevertheless by certain peculiarities in external characters, which have been supposed sufficient to justify the separation into individual races or breeds. Of these, three appear to be very distinct, the White or Caucasian, the Tawny or Mongolian, and the Negro or Ethiopian; and to one or other of these all the various forms which the human body assumes in different climates and countries may be referred.
The Caucasian race is distinguished by the oval shape of the head, the softened aspect, and symmetrical harmony of the general person, and the high degree of cultivation of which the intellectual faculties admit. The colour of the skin and of the hair varies. In warm climates the former is dark or olive-coloured, and the latter is black and glossy. In colder regions the skin is fair and light-coloured, or ruddy, and the hair becomes chestnut, fair, or even red.
The Mongolian or Altai race is distinguished by prominent cheek-bones, flat countenance, oblique eyes, parted by a small interval, straight black hair, slender beard, and olive, tawny, or copper-coloured complexion. This race has formed great empires in China and Japan, and has sometimes extended its conquests beyond the Great Desert; but its civilisation has remained stationary.
The Negro or Ethiopian race is confined to the south of the Atlas. Black complexion, crisp woolly hair, compressed skull, and flat nose, prominent mouth, and large thick or everted lips, form its distinguishing external characters. The tribes of which it consists have ever remained barbarous.
The first of these races, from which Europe, Asia, and the north and east of Africa have been peopled, is denominated Caucasian, because tradition and the natural affinity of nations seem to justify the opinion that this race had originally inhabited the mountainous range between the Caspian and Black Seas, from which it has spread by radiation. In confirmation of this, it may be observed that the tribes of the Caucasus, the Circassians, the Georgians, and the Armenians, afford at the present hour the most perfect and beautiful specimens of the human form. This race may be distinguished, by the analogy of languages spoken by them, into three principal branches.
1. The Aramean or Syrian branch, proceeding to the south, gave birth to the Assyrians, the Chaldeans, the Arabs ever unsubdued, and who, after Mahomet, aspired at the sovereignty of the world; the Phoenicians, the Jews, the Abessins, colonies of the Arabs, and probably the Egyptian or Koptic race. From this first branch, ever prone to mysticism, the most extended forms of religious belief have issued. Science and literature, occasionally flourishing among them, have, nevertheless, been always disguised or corrupted by fanciful ceremonials and a style highly figurative. 2. The Indian, German, and Pelasgic branch was much earlier divided into tribes, and much more extensively diffused. The most numerous affinities may nevertheless be traced between its four principal languages—the Sanscrit, at present the sacred language of the Hindoos, and the parent of all the dialects of Hindostan; the ancient language of the Pelasgi, the common parent of the Greek, the Latin, of many extinct languages, and of all the present dialects of southern Europe; the Gothic or Tudesch, from which are derived the languages of the north and north-west, for instance the German, Dutch, Anglo-Saxon, and English, the Danish, Swedish, and their dialects; lastly, the Sclavonian, from which are sprung the languages of the north-east, the Russ, the Polish, the Bohemian, and the Vend.
By this branch of the Caucasian race, philosophy, the sciences, and the arts, have been carried to the highest degree of perfection; and of these they may be regarded as the chief depositaries. In Europe this race is believed to have been preceded by the Celt or Titano-Celt, whose tribes, proceeding by the north, and formerly very extensive, were nevertheless confined to the most western points; and by the Cantabrians, who passed from Africa to Spain, and who are now almost lost among the numerous nations, the posterity of which is mingled in the European peninsula. The ancient Persians are derived from the same source as the Indians; and their descendants still bear the most conspicuous marks of connection with the European nations.
3. The Scythian and Tartar branch, bending first to the north and north-east, always erratic in the immense plains of these countries, have returned only to ravage the happier establishments of their brethren. From this branch issued the Scythians, who anciently distinguished themselves by incursions into Upper Asia; the Parthians, who destroyed the Greek and Roman dominions; the Turks, who subverted that of the Arabs, and subdued in Europe the last remnant of the Hellenic nation. The Fins and Hungarians are tribes of the same family disseminated among the Sclavonian and Judaic nations. The north and east of the Caspian, their native soil, still maintains tribes which have the same origin and speak similar languages; but they are intermingled with numerous other small septs of different origin and speech. The Tartar tribes remained more unchanged in that tract from which they long threatened Russia, which has at length subdued them, from the mouths of the Danube to beyond the Irtish. Their blood, nevertheless, has been mixed with that of the Mongols, many traces of which may be seen in the younger Tartars.
On the east of this Tartar branch of the Caucasian race begins the Mongolian, which thence extends to the shores of the Eastern Ocean. Its branches, still nomadic, the Calmucks and the Kalkas, roam the Great Desert. Three times have their ancestors, under Attila, Gengis, and Timour, spread the terror of their name among the settled inhabitants of Europe and Asia. The Chinese constitute the branch most early civilized, not only of this race, but of known nations. The Mantchoux, a third branch, who recently conquered, still retain, China. To the same race in great part belong the Japanese and the Coreans, and almost all the hordes which stretch to the north of Siberia, under the sway of the Russians. Excepting some learned Chinese, the whole Mongolian race are attached to the sects addicted to the worship of Fo.
The origin of this great race appears to be in the mountains of the Altai range, as that of the Asio-European is in the elevation of Caucasus. It is impossible, however, to trace the filiation of its branches with the same accuracy. The history of these nomadic nations is Human as transitory as their establishments; and that of the Chinese, confined to the bosom of their empire, furnishes only short and unconnected views of the contiguous nations. The affinities of their modes of speech are further too little known to guide us in this labyrinth.
The languages spoken in the north of the Ultra-Gangetic peninsula, as well as that of Thibet, present some relations, at least in monosyllabic character, with the Chinese; and the nations by whom they are spoken are not void of features of physical resemblance to the other Mongolian tribes. The south of this peninsula, however, is inhabited by the Malays, a much handsomer race, whose breed and language have spread to the coasts of all the islands of the Indian Archipelago, and have occupied the greater number of those of the South Sea. In the largest of the former, especially in the wildest places, dwell other tribes, with crisp hair, black complexion, and negro features, all extremely barbarous. The best known are denominated Papous, which may be applied to the whole.
Neither the Malays nor the Papous can be readily referred to any one of the three great races. The former it is difficult to distinguish from the neighbouring races on each side the Caucasian Indians and the Mongolian Chinese. The Papous may be negroes anciently cast away in the Indian Seas; but to determine this point we require both accurate figures and descriptions.
The inhabitants of the north of the two continents, the Samoieds, the Laplanders, and the Esquimaux, spring, according to some, from the Mongolian breed; according to others, they are degenerate slips of the Scythian and Tartar branch of the Caucasian breed.
The Americans have not yet been clearly traced either to one or other of the races of the ancient continent; yet they are void of character sufficiently precise and constant to constitute a peculiar race; their copper-coloured skin is inadequate; by the dark hair and slender beard they approach to the Mongols; but from these again they are distinguished by the well-marked features and the prominent nose. The modes of speech are as numerous as their tribes; and neither between themselves nor with those of the ancient world has any satisfactory analogy been traced.
Of the various breeds now enumerated, the Caucasian or Asio-European is supposed to furnish the most perfect model of the human frame; and from this, therefore, anatomists derive their descriptions both of the body at large and of individual parts and organs.
The structure of the human body may be studied in two modes, either as an assemblage of organic substances endowed with characteristic physical and vital properties, or as an assemblage of organs destined to effect particular and definite purposes.
The human body, like that of every other mammiferous animal, consists of several kinds of animal organic substances endowed with appropriate characters and properties. The substances thus distinguished have been named elementary textures, since into them, as into so many elements or integrant principles, the human body is supposed capable of being resolved. To enumerate these elementary textures, to ascertain their minute structure or organization, to investigate their distinctive properties, and to determine the extent to which they enter into the composition of particular organs, is the province of General Anatomy. In this department the anatomist, abstracting from the shape, position, and mechanical configuration of parts, studies only their intimate and distinctive characters as organic substances. The human body may further be regarded as an assemblage of organs, and sets of organs, destined to effect certain purposes. These purposes may be referred to two general heads; those which are common to plants and animals, and those which are proper to the latter. The first comprehends nutrition and generation, and have been named vital, organic, or automatic functions; the second embraces muscular action, sensation, and nervous influence or innervation, and are distinguished as animal functions. Since these purposes are effected by certain processes going on successively and simultaneously by the action of one or more organs, they are distinguished by the general name of functions, or orders of functions. Each function consists of several integral and individual processes; every process consists of one or more actions; each action depends on certain properties; and properties in living bodies, though mechanical, chemical, or vital, are always connected either with the intimate structure of parts or with the configuration of organs. Thus nutrition is at once termed a function, and is said to consist of the several functions of digestion, absorption, circulation, respiration, and secretion. Generation, on the other hand, is said to be a function consisting of several processes—the formation of germs or ova, the secretion of semen, impregnation, gestation, and exclusion. Of the functions proper to animals, muscular action, modified in various modes, produces locomotion, gesture, voice, and several motions necessary to the performance of nutrition and generation. Sensation may be said in all cases to depend on nervous action and the mechanism peculiar to each species of sensation. Nervous energy, again, may be said to consist of three properties, those of receiving, transmitting, and recognizing impressions. Lastly, a form of faculties connected with the immaterial or thinking part of the system peculiar to man constitutes what are named the intellectual functions.
This division of the phenomena of living bodies into certain assemblages or functions, has given rise to a similar division of these bodies into organs. An organ may be defined to be a part of a living body, of a definite shape, consisting of certain parts, composed of various elementary textures, the seat of one or more actions, and placed in a certain position and region. It rarely happens that one organ only is sufficient for the performance of a function. Several are commonly required to concur to the same general purpose; and hence the organs are arranged in classes, sets, or assemblages, according to the functions to which they are subservient. Thus the organs subservient to the function of digestion consist of the teeth, tongue, and mouth, as organs of mastication; General Anatomy, the pharynx and esophagus as the tube of deglutition; the stomach as the organ of chymification; the duodenum and small intestines as that of chylification; and the large intestines as the temporary receptacle of the excremential residue of food and drink. Such assemblages of organs have received, for want of better, the denomination of apparatuses; and the anatomist, when he designates a class of organs devoted to the performance of a specific function, is compelled to distinguish them as the apparatus of digestion, the apparatus of absorption, of circulation, of respiration, of secretion, and so forth. To this method of distinction it may indeed be objected, that scarcely in one instance are all the organs of any apparatus exclusively directed to the performance of the function of that apparatus; and an organ concerned in the function of digestion may also contribute to that of circulation or respiration. Thus the larynx, though more particularly the organ of voice, is also an organ of respiration; the tongue and teeth, though belonging in one sense to the organs of digestion, are not less important as those of speech; the diaphragm and abdominal muscles, though organs of respiration, are also accessory agents of digestion. These, however, are only to be regarded as examples of the ingenuity with which one organ in the animal body is made to answer several purposes; and since all arrangements are artificial, or bear relation, not to the purpose of construction, but to the mind of the observer, the best course is to choose that which is least so, and which makes the nearest approach to the apparent objects of nature.
To acquire a just knowledge of the organs of the human body, with the views now stated, it is requisite to study their external shape and configuration, their position and contiguous relations, their ordinary size and dimensions, the mechanical divisions of which they consist, their external characters and physical properties, their intimate structure and the elementary textures of which they are composed, their chemical constitution, their vital properties and consequent actions, and the uses to which they are obviously applied. The history of the organs, arranged upon these principles, constitutes the business of Descriptive, Particular, or Special Anatomy. The term Topographical Anatomy, which has also been proposed, is inadequate, since it indicates one class only of facts,—those belonging to local relations. That of Morphology is equally objectionable. The term Organology, though preferable by reason of greater generality, is not sufficiently appropriate to justify its adoption, to the exclusion of the one already in general use.
GENERAL ANATOMY.
The human body consists of solid and fluid substances, the former of which are organized, and determine the shape of the body and its parts. These organized solids are not in a strict physical sense solid and impenetrable. Most of them are soft, compressible, and elastic, by reason of the fluid matter contained in their interstices; and when deprived of this by desiccation, they shrink in various degrees, and lose both bulk and weight. The general ratio of the fluid to the solid parts has been already stated to vary from 7 to 1, to 9 to 1. An adult carcass weighing perhaps from 9 to 10 stones, has been reduced by desiccation to 7½ lbs. In short, a human body may be reduced to nearly the weight of its skeleton, which varies from 150 ounces = 9½ lbs. to 200 ounces = 12½ lbs.
These organized solids agree in the possession of certain general characters. Their internal structure appears to consist of a union of solid and liquid matter, which is observed to exude in drops more or less abundant from the surface of sections. The solid parts are generally arranged in the form of collateral lines, sometimes oblique, sometimes perfectly parallel, sometimes mutually intersecting. Such lines are denominated fibres, and occasionally filaments. In other instances the solids are observed to consist of minute globular or spheroidal particles, connected generally by delicate filaments. Most of these solids anatomists and microscopical observers have attempted to resolve into what they conceive to be an ultimate fibre or last element; but this inquiry leads beyond the bounds of strict observation.
Most of the solids may be demonstrated to be pen- General Anatomy.
Trated by minute ramifying tubes or bloodvessels, which traverse their substance in every direction, and in which is contained the greater part, perhaps the whole, of the fluid matter found in the solids. In a few in which ramifying vessels cannot be positively demonstrated, their existence is inferred by analogy from those in which they can. The filamentous, fibrous, or globular arrangement, with the distribution of arborescent vessels, constitutes organisation. The substances so constructed are named organised tissues (teles, textus), or textures, or simply tissues.
The organised solids also resemble each other in chemical constitution. They may be resolved into proximate principles, either the same or very closely allied. The proximate principles most generally found are albumen, fibrin, and gelatine, one or other of which, sometimes more, form the basis of every tissue of the human body. Next to these are mucus, and oily or adipose matter. Osmazome or extractive matter is found in certain tissues. And lastly, several saline substances, as phosphate of lime, carbonate of lime, soda, hydrochlorate of soda, are found in variable proportions in most of them. Of these principles albumen and fibrin, which are closely allied and pass into each other, are the most common and abundant. Osmazome, which is probably a modification of fibrin, is less frequent. These also are contained in the blood, and probably derived from that fluid. Gelatine, though not found in the blood, is nevertheless a principle of extensive distribution, being found in skin, filamentous tissue, tendon, cartilage, and bone. These proximate principles are resolved, in ultimate analysis, into carbon, oxygen, hydrogen, azote, phosphorus, chlorine, and sulphur. From the saline substances, calcium, potassium, sodium, chlorine, iron, manganese, and, according to some, titanium and arsenic may be obtained.
The organised solids, which enter into the composition of the human body, though agreeing in the characters now mentioned, differ, nevertheless, in other respects. The most remarkable differences of this kind consist in peculiarities in the arrangement of their constituent fibres, peculiarities in the nature of these fibres, and different proportions or modifications of their proximate chemical principles. From one or other of these circumstances the organised solids may be referred to the following 17 elementary tissues:—Filamentous or cellular tissue, including ordinary cellular membrane, and adipose membrane; artery, vein, with their minute communications, termed capillary vessels, and the erectile vessels; lymphatic vessel, and gland; nerve, plexus, and ganglion; brain, or cerebral matter; muscle; white fibrous system, including ligament, periosteum, and fascia; yellow fibrous system, including the yellow ligaments, &c.; bone and tooth; gristle or cartilage; fibro-cartilage; skin; mucous membrane; serous membrane; synovial membrane; and lastly, glandular structure, or the peculiar matter which forms the liver, the pancreas, the kidneys, the female breast, the testicle, and other organs termed glands.
These tissues may be distinguished into orders, according to the mode of their distribution in the animal frame. Several,—for instance filamentous tissue, artery and vein, lymphatic vessel, and nerve,—are most extensively distributed, and enter into the composition of all the other simple tissues. To these, therefore, which are named by Bichat general or generating systems, the character of textures of distribution may be applied. A second order, consisting of substances confined to particular regions and organs, and placed in determinate situations, viz., brain, muscle, white fibrous system, yellow fibrous system, bone, cartilage, fibro-cartilage, and gland, may be denominated particular tissues. To a third order, consisting of substances which assume the form of a thin membrane, expanded over many different tissues and organs, may be referred skin, mucous membrane, serous membrane, and synovial membrane, under the denomination of enveloping tissues. It may indeed be objected that the circumstance of mechanical disposition is insufficient to communicate a distinctive or appropriate character, and several of the tissues referred to the second head, e.g., fascia, must, on this principle, be referred to the third. The objection is not unreasonable. But it may be answered that it is almost vain to expect an arrangement entirely faultless; and the present is convenient in being, on the whole, more natural, and therefore more easily remembered, than any other. A distinct idea of it may be formed from the following tabular view.
| General or Common Tissues | Particular Tissues | |---------------------------|-------------------| | Filamentous tissue | Capillary vessel | | Artery | Vein | | Lymphatic vessel | Nerve | | Brain | Muscle | | White fibre | Ligament | | Yellow fibre | Periosteum | | Bone | Cartilage | | Fibro-cartilage | Gland | | Skin | Enveloping tissues | | Mucous membrane | Serous membrane | | Synovial membrane | |
The Fluids or Liquids.
The fluids of the animal body are various, but may be distinguished into three sorts; the circulating nutritious fluid named the blood; the fluids which are incessantly mixed with the blood for its renewal; and those which are separated from it by secretion.
I. The blood is well known to be a viscid liquid, of red colour, peculiar odour, and saline, something nauseous taste. Its temperature in the living body is about 97°; its specific gravity is about 105 to water as 100. Its quantity is in the adult considerable, varying from seventeen and nineteen pounds (Lehmann) to thirty pounds.
The colour of the blood varies in different parts of the system. In the left auricle, ventricle, and arterial trunks generally, its colour is bright scarlet, a tint which it loses in the capillary vessels. In the veins, venous trunks, right auricle, right ventricle, and pulmonary artery, its colour is a dark or purple-red, or Modena. As it moves from the trunk and branches through the minute divisions of the pulmonary artery, it gradually parts with this tint; and in the branches of the pulmonary veins it is found to have acquired the bright scarlet colour which it has in the left auricle, ventricle, and aorta. Hence the Modena or dark-coloured blood is distinguished as venous, or proper to the veins; and the bright red or scarlet-coloured as proper to the arteries.
According to the results of microscopic observation, blood globules consists of red particles suspended in a serous fluid. On or blood the shape of these red particles various opinions have been entertained. Generally represented as globular, Hewson describes them as flattened spheroids, or lenticular bodies, a view which is partly confirmed by the observations of Prevost and Dumas, of Beclard, of Hodgkin and Lister, of Gulliver and Wharton Jones. The opinion of Home and Young, that the flattening of these globules is a process posterior to the discharge of the fluid, is not improbable. These particles have, indeed, since the time of Hewson, been almost universally represented as consisting of a cen- The corpuscles are largest in size in what are called the Amphibia, including the frog, toad, triton, and siren. In the frog, the long diameter is \( \frac{1}{4} \) th part of one inch, the short diameter \( \frac{1}{8} \) th. In the siren, the long diameter is \( \frac{1}{4} \) th part of one inch, and the short diameter \( \frac{1}{8} \) th part of one inch.
In the large Ruminants and Rodents the corpuscula are larger than in the small species. The Ferre, if arranged according to the size of the corpuscula, would assume the following order: the seal, dog, bear, weasel, cat, viverra. Among genera of doubtful affinity, if regard be given to the size of the blood-corpuscula, the hyena would be arranged with the Canide, Bassaris with the Ursine family, and Cercoleptes with the Viverridae. In the fox the corpuscles are smaller than in the dog.
In the Frog, salamander, and other lower vertebrated animals, the large Corpuscula consist of a thin, transparent vesicular covering, enclosing another body in general oval, which appears to be solid, and surrounded by a quantity of soft red coloured matter. This inclosed body has been named a nucleus. When weak acetic acid is dropped upon these corpuscula, the colouring matter is removed, the nucleus becomes distinct, and the envelope is rendered faint. Strong acetic acid dissolves the envelope, and the nucleus escapes.
Some observers have attempted to demonstrate an analogy between the nucleus of the lower vertebrata and the central spot of the human corpuscula. But according to the testimony of the most careful observers, it is not possible to recognise in the corpuscula of the Mammalia any body similar to the nucleus of the lower vertebrated animals.
When blood is drawn from the vessels and immediately afterwards examined by the microscope, the red corpuscula are observed dispersed in a confused manner in the liquor sanguinis, as is represented in Fig. 2. In the course of half a minute or a little longer, the red corpuscula are seen to overlap each other, and assuming the appearance of standing on their edges, to be applied to each other by their broad surfaces, like a pile or rouleau of coins. In a small quantity of blood several piles or rolls of blood-disks are in this manner formed; the direction of these is not exactly straight, but often slightly curved; and the rolls intersect each other so as to form interstitial spaces. In the case of healthy blood, these intervening spaces are small. In the case of blood that is drawn during the state of inflammation, they are larger.
---
**Fig. 1. Red corpuscula of healthy blood dispersed confusedly in liquor sanguinis (W. Jones).**
- **2.** Arrangement of the red corpuscula like coins in rolls, when beginning and when fully formed. - **3.** The irregular net-like arrangement of the rolls of red corpuscula in healthy blood. Meshes small. - **4.** The net-like arrangement of the same rolls presented by buffy blood. The meshes are large. Henle admits two sorts of blood corpuscula; the one coloured, those namely belonging to the vertebrated animals, and especially to Mammalia, Birds, and Fishes; another sort, colourless, found mostly in the lower vertebrated animals, as the frog and triton, and in the Aspondylous animals. These are the same as those called lymph-globules. They are smaller in size than the coloured globules; those in the frog being 0.005 in diameter, according to Wagner. The proportion of these colourless globules to the coloured particles, varies according to rate of feeding and other circumstances. After the blood of a healthy frog has stood two hours, there are, in one drop of the upper stratum, among 55 coloured globules, 76 colourless particles.
Discharged from the vessels, the blood exhales, during the process of cooling, a thin watery vapour, consisting of water suspending animal matter capable of impressing the sense of smell, and undergoing decomposition. During the same space it is observed to be converted into a firm mass, which, though still soft and elastic, is entirely void of fluidity. As this process advances, a thin watery fluid, straw-coloured, not perfectly transparent, is observed to exude from every part of the solid mass, which also diminishes in size, till at length it is found floating like a tolerably thick cake in the thin watery fluid. The thick solid mass is named the clot or coagulum; the watery fluid is denominated serum; and the process of the separation, which is spontaneous, is termed coagulation. The blood at the same time is said to discharge carbonic acid.
The clot, if divided and washed in water often changed, or in alcohol or aqua potasse, may be deprived of its red colour, and made to assume a gray or bluish-white tint. This gray mass, which is tough, coherent, opaque, and more or less dense, homogeneous, but void of traces of organic structure, consists chiefly of albumen or fibrin, or a substance partaking of several of the characters of both. To this substance the blood owes its viscidity and its property of spontaneous coagulation; and from the circumstance of its resemblance to the lymph or albuminous fluid which is effused from wounds and inflamed surfaces, and to the fibrin of muscle, and the albumen of many of the tissues, it may be regarded as the most vital and nutritious part of that fluid. It is a mistake nevertheless to assert, as is done by Beclard and others, that this substance presents to the microscope the aspect and structure of muscular fibre. Its aspect is by no means so regular as this, nor can its particles be said to present traces of organic structure or arrangement.
The red matter removed by washing is a mixture of serum, of globules, and of a peculiar colouring matter. Modern chemistry shows that the latter is a particular substance, insoluble in water, but susceptible of suspension in it to an extreme extent, and consisting of animal matter combined with peroxide of iron. It is distinguished by the name of zoohematine, haematin, and haematosine. Deprived of this, the globules are estimated by Bauer at 2500th of an inch in diameter.
Another principle or element which it has been believed important to distinguish is, that which has been named Globuline. This forms the principal part of the blood globules, indeed, the whole of them excepting the haematosine, or colouring principle. Globuline is an albuminous substance; it has not been obtained in a pure state; but it possesses the composition and characters of albumen. By stirring blood so as to separate the fibrin, and mixing it with six volumes of a saturated solution of sulphate of soda, and then boiling the mass with alcohol acidulated with sulphuric acid, sulphate of hirnatosine is dissolved, and sulphate of globuline remains. This is gray or white, and is said to contain four atoms of sulphuric acid and one of proteine.
The serum, with the taste and odour of the blood, rather alkaline, coagulates at 162° F. or on the addition of acids; separation; nitrate of silver, or corrosive sublimate, and then resembles boiled white of egg. The coagulated matter is albumen; and a little water containing soda and salts of soda may be separated. It is a remarkable difference between this albumen, which is suspended in the serum, and that which constitutes the clot, that while the former requires heat as a re-agent, the latter assumes the solid form spontaneously.
The specific gravity of arterial serum is 1022; of venous serum 1026.
The proportion of serum to clot varies in different animals, in different individuals, and in different states of the system.
In the human body a quantity of five ounces of blood usually furnishes about one ounce and two drachms, or one ounce and four drachms of serum. In inflammatory diseases the amount of the serum is usually increased. In fever, on the contrary, the proportion of serum is diminished, especially at advanced periods of the disease. But the clot is at the same time less firm than usual, and is soft, loose, and flabby. This seems to show, that the force with which the blood is coagulated is diminished.
Liquid fibrin, or the spontaneously coagulable part of the blood, is most abundant in warm-blooded animals; and among these it is more abundant in the blood of Birds than in that of the Mammalia. In Fishes it is scanty; and it is also sparing in the blood of the Reptiles and Amphibia.
It is a well-known fact, that in frogs the blood does not coagulate on exposure of the vessels to air, as it does in the Mammalia. This must be owing, either to the blood of these animals containing a much smaller proportion of fibrin than that of the Mammalia, or the fibrin having much less coagulating power.
This property of spontaneous coagulating power has been supposed by Saisy and others to bear some relation to the state of respiration, or what may be denominated the intensity and energy of that function in the different classes of animals; and the idea seems accordant with the facts. In Birds the function of respiration is most fully developed. In Reptiles and Fishes it is very imperfectly developed.
When blood, drawn from the veins of a person labouring under acute rheumatism and other inflammatory diseases, is Sanguinis undergoing coagulation in a glass vessel, a colourless fluid or Plasma, may be perceived round the edge of the surface; and, after an interval of four or five minutes, a bluish appearance is observed from the formation of an upper layer of the blood, in consequence of the subsidence of the red particles to a certain distance below the surface, and the clear liquor being left between the place of the red particles and the edge of the vessel. This liquid may be collected by a spoon and placed in another vessel, where it is first clear, though opalescent, viscid, homogeneous. After some time, however, it undergoes separation into two parts, one coagulated, the other fluid. The coagulated part is the fibrin of the blood, or that which is spontaneously coagulable; the fluid part the serum. The opalescent liquor has been named Liquor Sanguinis (Babington).
To this the name of Plasma has been given by Miller, Henle, and other German writers. The former by filtering the blood of the frog, which coagulates very slowly, causing the larger corpuscula to be retained by the filter, and the liquor sanguinis to come through clear and colourless, obtained it in a separate form.
---
1 Some Considerations with respect to the Blood, &c. Medico-Chirurgical Transactions, vol. xvi., p. 293. From the facts now stated, it seems reasonable to infer, that the element of the blood which is called Liquor sanguinis and Plasma, is the coagulable part, or the albuminous or fibrinous, freed from the colouring matter and the serum.
In 1830, Dr Babington found a yellow concrete oil in blood in the state of health; Boudet, in 1833, found in the serum a peculiar oily or fat matter, to which he gives the name of seroline, and which melts at 97° F.; and Gmelin, Chevreul, and Lecanu, obtained from the blood stearine and elaine. In certain morbid states these adipose principles are liable to become greatly increased in amount, and their presence then renders the serum opaque and milky-like. The globules are often at the same time deficient (Lecanu).
The chemical constitution of the blood and its elements has been examined by many chemists with different degrees of accuracy and completeness. It may be sufficient here to advert to the results of those given by Denis and Lecanu, the former of which was given in 1830, and the last was published in 1837.
In the first place, it is to be observed, that one thousand parts of blood consist of 869 parts of serum, and about 131 parts of what has been named coagulum, that is, globules and colouring matter.
In the second place, it is admitted, that the serum contains all the immediate principles of the blood, excepting fibrine and colouring matter; that the fibrine and colouring matter make part of the globules; and that the serum represents exactly the fluid, in the midst of which, during life, the globules float; while the clot or coagulated portion represents the globules themselves, though in a state more or less deformed and altered.
For these reasons, chemists in ascertaining the chemical constitution of the blood have subjected the serum only to accurate analysis.
The two following tables exhibit the quantitative analyses of the serum, as given by Denis and Lecanu.
According to Denis.
| Substance | Parts | |--------------------|-------| | Water | 900-9 | | Albumen | 80-9 | | Soda | 0-5 | | Lime | 0-2 | | Magnesium traces | | | Sulphate of potash | 0-8 | | Phosphate of soda | 0-4 | | Chloride of sodium | 4-0 | | Oleic acid and mar- | | | garate of soda | 3-0 | | Volatile sebatic acid | | | Phosphate of lime | 0-3 | | Yellow biliary colouring matter | 3-0 | | Blue colouring in traces | |
According to Lecanu.
| Substance | Parts | |--------------------|-------| | Water | 906-09| | Albumen | 78 | | Extractive matters | 3-79 | | Fat matter | 2-20 | | Hydrochlorates | 6-5 | | Potash | 5-82 | | Subcarbonate of lime and magnesia | 0-91 | | Phosphate of lime and magnesia | 0-87 | | Loss | 1-41 |
These tables show the substances contained in the blood taken as a whole, and the proportions, as nearly as may be, in which each substance is contained. But it is of consequence to ascertain, as nearly as may be practicable, the proportion in which these articles are present in the serum and the globules respectively. This Lecanu attempts to exhibit in the following table, which he gives as representing in man the medium composition of the venous blood in the normal state.
Free oxygen, ... azote, ... carbonic acid, Extractive matters, Fat phosphated matter, Cholesterine, Seroline, Free oleic acid, Free margaric acid, Hydrochlorate of soda, ... of potash, ... of ammonia,
Sulphate of potash, Carbonate of soda, ... lime, ... magnesia, Phosphate of soda, ... lime, ... magnesia, Lactate of soda, Salt with fat fixed acids, ... volatile and yellow colouring matter,
Albumen, Water, Fibrin, Hematosine, Albumen,
Further, if we suppose that one thousand parts of blood give
869-1547 of serum, 130-8453 of globules,
these numbers may then be represented in distribution in the following manner.
869-1547 Serum. 130-8453 Globules.
The main point which it is important to know, is that blood consists of albumen and fibrin to the extent of between 78 and 81 parts in the thousand, suspended in about 902 parts of water, with some adipose matter, and salts, chiefly of soda, potash, and lime. Though these saline substances are neutral, yet in general the blood presents an alkaline reaction, which is ascribed to a slight predominance of soda. In persons and animals that subsist much on vegetable food, this alkaline reaction ought also to depend on the presence of potash.
The blood may be believed to contain all the substances which are found to be present in the different textures and organs. It either does so, or it contains their material elements, excepting in one instance. It contains, so far as is hitherto known, no gelatine. According to Marchand, it contains a little urea. But in the healthy state, this is in exceedingly small quantity.
The blood, that is, the serum, has in the normal state an alkaline reaction, which is ascribed to the presence of phosphate of soda, not carbonate. The saline matter is of use in maintaining the fluidity of the blood; in contributing to General its red colour (Stevens); and probably it may be useful in contributing to certain galvanic or electro-magnetic actions in different organs.
Chemical constitution.
From the blood and its elements the animal tissues derive the materials of their nutrition, and the different secreted fluids are formed.
Arterial blood differs from venous according to Leucanu, besides the difference in colour already mentioned, chiefly in the following circumstances.
It contains a larger amount of globules, a greater proportion of fibrin, an amount of albumen, extractive matters, saline and fatty matters, to all appearance equal, more oxygen in proportion to its carbonic acid, less combined carbon and oxygen. In consequence chiefly of the larger proportion of globules, it shows a greater tendency to coagulation, and the clot is more bulky, more firm, and gives a small proportion of serum. Its density is to that of venous blood as 1050 to 1053 (J. Davy).
The proportion of serum is smaller, and the proportion of globules greater in man than in the female; in the blood of sanguine persons than in the blood of lymphatic individuals of the same sex; in the blood of adults than in the blood of children and of the aged; and in the blood of persons well fed than in those imperfectly nourished.
The blood of the portal vein contains a smaller proportion of globules and a larger proportion of water, serum, and fat, than the blood of the venous system in general.
The blood of the placenta is greatly more rich in globules, and contains less water than the blood of the veins.
In the fetus, the blood contains little coagulable matter; and this principle is entirely wanting in the blood of the menstrual discharge.
II. The fluids received by the blood are chyle and lymph. Chyle is derived from chyme, a gray pulpy substance, formed from the alimentary mass in the stomach and duodenum. Detached from this substance, and received by the chyliferous tubes, it is whitish and scarcely coagulable. In the mesenteric glands, it becomes more coagulable, and assumes a rose colour. Lastly, in the thoracic duct, and before joining the mass of blood, it is distinctly rose-coloured, coagulable and globular in its particles. In the branches of the pulmonary artery it appears to become perfect blood. Lymph is a colourless, viscid, albuminous fluid, imperfectly known.
The globules or corpuscula of the chyle, of the thymus fluid, and of the lymph, appear delicately granulated on the surface. They are generally globular or lenticular, never following the differences in shape and size of the blood-disks in different classes of animals, nor in birds affecting the long oval figure of the nucleus of the red corpuscle.
The globules of chyle, thymus fluid, and of lymph, are smaller than the colourless globules of the blood. They also differ in structure. In the last, two, three, or four nuclei are seen when the envelope is made more or less transparent by acetic, sulphuric, citric, or tartaric acid. But the globules of chyle, of lymph, and of the thymus fluid, like the nuclei of the red corpuscula of the blood, are only rendered more distinct and smaller by any of these acids, so that the central part presents no regular nuclei, or divided nucleus, such as are contained in the colourless globules of the blood. In short, according to Mr Gulliver, who has examined these bodies with great care, the colourless globules of the blood have the character of elementary cells, while the globules of chyle resemble, and probably are, nuclei or immature cells.
The microscopical and chemical characters of the globules of the chyme, of the thymus, and of the lymphatic glands, are nearly the same. When quite recent, they swell on being mingled with pure water, as does the nucleus of the blood corpuscle. When well mixed with a strong solution of alkali, or of a neutral salt, the globules undergo partial solution, become misshapen or faint, forming a ropy tenacious compound with the fluid (Gulliver).
III. Of the fluids separated from the blood, all cannot be said to belong to the animal body. Several,—for instance, fluids, the perspired fluid of the skin and lungs, the fluid of the cutaneous and mucous follicles, and the urine,—become, after secretion, foreign to the body, and require to be removed. Those belonging to the body are such as are prepared for some purpose within it, and after this are either re-absorbed, or, being decomposed, are expelled. Of the former kind, fat, serum of serous membranes, and synovia, afford examples. To the latter description belong tears, saliva, gastric juice, pancreatic fluid, bile, the seminal fluid of the male, and the milk of the female, all of which are the result of a distinct glandular secretion for a specific purpose, after which they are expelled from the economy.
Of the fluids secreted upon the surface, or on different points of the alimentary canal, some are alkaline, some acid; but all agree in possessing some albuminous or albuminoid principle, which is believed to act by what is called catalysis, or being placed in contact with foreign bodies introduced, to act on them, either by inducing chemical changes, or by causing actions of assimilation.
1. Thus saliva contains salivine, a species of diastase, besides sulphocyanic acid, chlorides, lactates, and phosphates. It is alkaline when food is taken, and during mastication.
2. Gastric juice contains pepsine and chlorine or hydrochloric acid, and, according to some, lactic acid.
3. Bile contains cholic acid or biline, taurine, free soda, and the salts of the blood; while taurine, which is an albuminoid principle, contains sulphur. Thenard and Gmelin found in it picromel. Bernard states that the liver forms sugar.
4. Pancreatic juice contains, besides an albuminous principle, which may be named Pancreatinine, according to the observations of Bernard, free soda, which gives it an alkaline reaction.
5. The intestinal fluid (Succus intestinalis) has a reaction, sometimes acid, sometimes alkaline.
Urine may be regarded as urea suspended or dissolved in water. Urea is the peculiar and characteristic element of the secretion. It contains also a little uric acid, which is probably produced from the urea, as this acid can scarcely be said to be a constituent of healthy urine. The other ingredients are saline matters common to the blood and the urine or complementary between them.
The density of healthy urine varies from 1015 to 1033, water being as 1000; and the average, as determined from the examination of the urine in fifty instances of persons in good health, is at the highest 1026 and at the lowest 1017. The general average, therefore, amounts to 1022. This is understood while the quantity discharged daily is from 45 to 53 ounces, which is about the general average in healthy individuals who consume liquids at the ordinary rate.
This density above that of water, urine owes to the presence of urea and saline matters. If the urea and saline matters be increased, the density of the urine is increased; if they be diminished, the density of the urine is also diminished.
It may here be observed, that urea is the form which the elements of the fibro-albuminous parts of the blood assume, after these fibro-albuminous principles have been employed in repairing the waste of the tissues. If the proximate chemical principles of albumen be compared with those of urea, it is seen that the latter are the complement of the former. Thus,— Thus while albumen and urea contain the same proportion of oxygen, the former contains one-seventh more hydrogen, three-fifths more carbon, and two-thirds less nitrogen. It is known that the former proportions of these principles are employed in repairing the waste of the albuminous tissues, especially the muscular system; and while carbon and oxygen are discharged by the lungs, and carbon, oxygen, and hydrogen by the liver, the large superfluous portion of nitrogen not required, namely 31 per cent., uniting with hydrogen, oxygen, and carbon in the form of urea, is left to pass through the blood, and by means of the kidneys to be expelled from the system.
In the healthy state urine is always slightly acid when discharged. This acidity is liable to become excessive on the one hand; and on the other to diminish so far as to render the urine alkaline. This change is much favoured, if not wholly occasioned by the presence of mucus, purulent matter, or other azotised substances.
BOOK I.
CHAP. I.—FORMATION, DEVELOPMENT, AND ULTIMATE ANALYSIS OF THE TISSUES.
It has, at different times, in the history of Anatomy and Physiology, been an object with various ingenious observers to trace to some one simple element all the different forms which the animal textures assume. In general, however, these attempts have not been successful, and have led to generalisations too great to be just, and more fanciful than to be founded in careful observation.
In the year 1773 William Hewson communicated to the Royal Society his account of the Red Particles of the Blood, making known among other points the fact of the existence in them of an opaque central spot, and of an opaque body in the globules of the oviparous vertebrated animals. The application of this fact it was not easy at that time, perhaps not possible, to discover. After the lapse of sixty years, in 1833, Robert Brown, well known as a skilful botanist, in Observations on the family of the Orchideae, in the Transactions of the Linnean Society, made known the existence of a vesicular or celliform body containing a solid, to which he gave the name of Areola or Nucleus of the cell. The signification, however, of this structure was little or not understood. At length in 1838, J. M. Schleiden, professor of Botany in the university of Jena, made known the fact, that when a slice from the succulent part of certain plants is examined under the microscope, part of it appears to consist of an infinite number of minute vesicles, rounded or polygonal, generally flattened, coloring by the margins, and containing in their interior matters coloured or colourless. This appearance is most perceptible in various monocotyledonous orders, as Orchidaceae, Commelinaceae, and Asphodelaceae, and many dicotyledonous orders, as the Cactaceae, Balanophoraceae, &c. But it is also found in different degrees of distinctness in the greater part of the vegetable world. This close vesicle generally contains a fluid, sometimes jelly-like; but it also contains a body more or less rounded, to which Schleiden applied the name of Cell-Kernel General and Cytoplasmus. It is attached on one side to the inner surface of the vesicle, but on the other is free. When perfectly formed it is a flat, lenticular, sharply defined, transparent, pale-yellow body, in which it is possible to distinguish one or two, seldom three, hollow corpuscula. These are called nucleoli.
The Cytoplasm is represented by Schleiden to be a nitrogenous body or protein compound, perhaps in its simplest state pure proteine. Its minuteness is almost inconceivable, being from 0'00009 to 0'0022 of one inch in circumference.
The Cytoplasm has been more generally known under the name of Nucleus; and the vesicle containing it has been called Nucleated Cell; (Cellula Nucleata); Elementary Cells; Primary Cells.
In 1839, the year following that in which Schleiden published his doctrines on Phytogenesis, or the formation of plants, Schwann made known the fact, that in the animal tissues the same structure exists which Schleiden had shown is found in those of the vegetable world. The fact has been stated in general terms by Henle in the following manner. In most vegetable and animal tissues, there exist during the whole period of life, or a certain time of the development of these tissues, microscopical corpuscula of peculiar and very characteristic shape. These are minute bladders or vesiculae, consisting of a fine enclosing membrane and a fluid, occasionally something granular, content. In the wall of these vesiculae lies a smaller darker body, namely, the Kernel or Nucleus of the cell,—Cytoplasm of Schleiden; and this is generally distinguished by one or two, rarely more, darker and almost regularly round specks (Nucleoli).
It is here to be observed, that nucleated cells as thus described are not perceptible in the tissues at all times of their existence. It is chiefly in the early period, or that of formation and development that they are observed. The process of cell-formation is in truth progressive; and this circumstance has led Schwann, Henle, and others, to speak of the life of the cell and of its youth or early period of existence, though Henle himself makes an apology for the use of the term youth in this manner.
The cells lie in a shapeless or amorphous matter, the Cytoplasmata, in which they float when this is fluid, and are imbedded when it is semi-solid or solid. The solid Cytoplasmata, in which the cells are more or less compressed, appears like inter-cellular substance, and is also the connecting medium of the cells.
What is now stated embraces almost all the points in which observers are agreed. Upon all others minute but real differences of opinion exist:—upon the nature and composition of the cell, upon the mode in which cells are developed and multiplied, and upon the transformations which they undergo.
The covering or wall of the cell is allowed by most to be an albuminoid or protein substance. It is rendered transparent and indistinct, but not dissolved by acetic acid. The contents of cells are semifluid, often granular, that is, consisting of small grains or bodies differently coloured, of fat particles, and of a fine molecular substance, that is minute atoms, the nature of which is unknown.
On the nature and general characters of the body called the Nucleus, opinions are discordant. In some instances the nucleus has the appearance of a granular body, more or less solid, while in other instances it has that of a pale vesicle, with a distinct cell-wall and fluid content. The pale vesicular form is the most general, and, according to Kölliker, it is the constant form of the early stages of the life of the cell. That the composition of the nucleus is different from that of the cell, is shown by the fact, that many agents which act upon the one, have no effect upon the other. Kölliker is of opinion, that the membrane of the nucleus is composed of pyrin, the clear content of albumen, and the nucleolus of fat.
In the animal tissue cell, as in the vegetable cell, the nucleus is commonly situate on the wall of the cell, apparently imbedded in its substance, but according to Schwann most frequently attached to its inner surface. Occasionally the nucleus is situate towards the centre of the cell, as is the case in the cells of cylinder epithelium.
The phenomena now mentioned are most easily seen in cartilage in its early or growing stage.
On the mode in which Elementary or Primary Cells are themselves formed, different representations have been given by different observers. In general a nucleus is first formed; and even upon this process different views are given. According to Schleiden and Schwann, in the Blastema or plastic fluid nucleoli first appear; and as new matter continues to collect, round one or more of these, the nucleus is formed. Afterwards, matter deposited on the nucleus forms the cell-wall or vesicular membrane. Henle, on the other hand, thinks, from various facts, that a Nucleus may be formed independent of any Nucleolus. He supposes in the blastema the existence of elementary particles or granules, which, he says, are found wherever new formations are taking place; for instance, in the yolk of the egg, in milk, in chyle, and in lymph, in the delicate commencements of glands, and the epithelium, when rapid regeneration takes place, and in pathological fluids.
These elementary granules are for the most part, as far as can be ascertained, composed of fat, and a membrane inclosing the fat-drops; and he adduces, in proof of the correctness of this view, the fact made known by Ascherson, that when oil and albumen are allowed to unite in small drops, there are formed minute corpuscula, consisting of fat, inclosed in an albuminoid membrane.
It appears, in the second place, that, in certain circumstances, cells are formed without the previous existence of a nucleus. Thus, in addition to the fact, that in cryptogamic, and many higher plants, a minute spherule first appears, soon becomes a vesicle, and is eventually formed into a cell; in the chorda dorsalis of fishes and reptiles, cells are formed without the previous formation of any nucleus. It is to be remarked, however, that even in this instance, nuclei appear after the cells have been formed.
In the third place, it is observed that cells and nuclei are in certain circumstances formed simultaneously. Thus, in the embryonic cartilage of the toad, the formation of both bodies is so simultaneous, that Vogt never could detect nuclei without a cell-wall, or cells which did not enclose a nucleus.
On the mode in which cells are reproduced and multiplied, several conjectures have been formed, but nothing can be said to be ascertained. It is the opinion of Schwann, for the subject cannot be said hitherto to admit of proof, that the continued increase of cells is in most cases effected, though he does not show how, in the plastic fluid or blastema. In other instances new cells are formed within cells which had previously existed; and by these they are surrounded, until they have attained, by growth, a certain size, when they escape, apparently by rupturing the original or parent cell. This is supposed to be illustrated by the process of what is called cleavage in the ovum, and by what cell-formation takes place in the cells of cartilage. But, excepting in these instances, this process of cell-multiplication, which has been termed endogenous, though common in vegetable productions, is rare in the textures of the animal world.
It was believed, with considerable confidence, when the discovery of the existence of elementary cells was made known that an easy and intelligible method was found of explaining the formation of all the textures which enter into the composition of the animal body. It is quite possible that this belief is well-founded; and in a few instances probably it may be said to be in a slight degree realised. But it must not be concealed, that the whole theory is in a state of imperfection and transition; and that it is far from presenting those clear, certain, and consistent phenomena, which might be applied with any confidence in explaining the growth and visible structure of the several tissues of which the animal body is composed. It is manifest, that in order that the cell and its nucleus should be the means of forming these tissues, they should undergo certain transformations. Now, upon these transformations, and upon the mode in which they are effected, observers are by no means agreed. In some instances it appears that the cell is the agent of transformation and creation, and in others it is the nucleus that is believed to be the agent. Schwann supposed, that to form certain tissues, as the Cellular, that is the Filamentous, the Tendinous, and the fibrous or Ligamentous, the cells become elongated and were thus converted into fibres. But though such elongation seems to take place in certain circumstances, the doctrine has not been generally admitted.
The tissues in which the agency of cells and their nuclei are believed with least certainty to be seen, are cartilage in its early state, bone in a certain degree, tooth, nerve-substance, arterial tissue, muscle, adipose membrane, and the secreting glands, as the liver, the kidney, the pancreas, the salivary glands, the female mamma.
The appearances observed during the growth of Nerve-Fibres in the embryo, particularly by Schaffner and Kölliker, are thought to afford good examples of the influence, if such it may be called, of the nucleated cell. In the earliest period of its formation, nerve substance consists almost entirely of round, mostly nucleated, cells, filled with a fine granular material, and, with the exception of being somewhat smaller, exactly similar to the nerve corpuscula, found in the nervous centres of the adult animal. As development advances, many of these cells send forth fine tubular processes of a structure apparently homogeneous, which unite with similar processes from other cells, and thus eventually gave rise to continuous Nerve Tubules. Kölliker finds that in young batrachoid reptiles, a complete net-work of nerve tubules is formed by this junction and coalescence of the processes from branching cells. A similar observation was made by Schwann. In this particular instance, therefore, it appears, that Nucleated Cells, by sending out some shoots, and uniting with similar offsets from other cells, eventually form tubulated structures. According to Schaffner, as the nerve tubules coalesce and increase in size, the walls of the cells from which they proceed are gradually drawn out, and merge into the walls of the tubules, while the granular content becomes continued and identified with the content of the tubules.
Henle gives schemes or plans of the mode in which the General nuclei are transformed into the higher tissues; and Kölliker subsequently gave his representations of the process. It was supposed by Schwann, that the nucleus disappears shortly after the cell is completely formed. But according to Retzius, Henle, and Kölliker, the nucleus is a main agent of development in many tissues. The only parts in which, according to Henle, the nucleus disappears, are the blood-globules, the cells of the epidermis and the nails, most of the fat-cells, the tubules of the crystalline lens and of tooth-enamel, and many of the cartilage corpuscula. But in all fibres or fibriform tissues, supposed to be formed from coalescing cells, excepting those of the lens and of enamel, the nuclei not only remain persistent, but they undergo, or are the agents of, certain transformations.
First, they assume an oval shape, then gradually elongating and becoming narrow, they are converted into fine dark streaks, which lie straight, angular, or curvilinear, or for some space serpentine upon their proper cells. The Nucleus corpuscula then disappear. By reason of their sharp outlines, these streaks look like fibrous tissues, and are frequently taken for elongated cells, in which case the intermediate substance is overlooked or considered as cellular substance. At this stage, sometimes the absorption of the Nucleus commences by being divided into a row of minute dots, which constantly become paler and smaller. Similar rows of minute dots are found in all fibrous tissues, and most numerously in the cornea and in the organic muscles.
In opposite cases the elongated Nuclei gradually form a mutual connection by means of threads which each send out, and which, at first delicate and pale, gradually acquire the strength and firmness of the dark corpuscula from whence they proceed.
In consequence of the representations now given, Henle distinguishes two kinds of fibres:—namely, Cell-fibres and Nuclei-fibres; the former being those in which cells are split or divided into fibres, and the latter into fibrils; the latter those in which the nuclei are elongated, and by mutual union form fibres. The latter, again, he distinguishes into two different types, according to the original position of the nucleus on the surface, or on the edge of the flat nucleus-fibre; and the position of the nucleus is regulated by the form of the Cell-Fibre. Perfectly flat nuclei-fibres have the nucleus on the surface; cell-fibres, which approach the cylindrical form have the nucleus on the edges. To the latter order, he states, belong the fibres or filaments of the cellular tissue (teela conjunctiva), the fibres of the cornea, and those of tooth-bone.
The nuclei and nuclei-fibres are represented by the same anatomist to be of much use in forming the texture of the bloodvessels. In the development of these tissues, layers of cytotlastema are deposited in the form of structureless membrane; in these nuclei are formed, and undergo various changes. In the innermost layer, cells grow round the nuclei, and form the epithelial coat of the vessel. In the next layer, which forms what has been usually called the inner coat of the vessel, the nuclei remain unchanged. In the formation of the fibrous or elastic contractile coat, the nuclei are elongated, and arrange themselves in rows or lines, in the manner already mentioned.
The second type of Nucleus-Fibres, which are arranged on the surface of the flat Cell-Fibres, are distinguished by the tendency which they manifest to shoot lateral branches, and in this manner to form junctions with other lateral branches and make a network which covers the layer of cell-fibres; so that in the normal development they are situate between two layers of cell-fibres. This mode of development may be seen in the tissues of the bloodvessels, both arteries and veins, and in the muscular coat of the viscera.
The whole of this doctrine, however, is yet in a state of uncertainty and contradiction; and it would be unprofitable in this place to spend more time upon it. Whenever under particular heads it is possible to state any well-authenticated facts, this shall be done, so far as the limits and nature of this article admit.
The only subject which it is required further at present Relation to notice, is the relation between the nucleated cells and between the corpuscula of the blood. This subject is still, notwithstanding the observations of several skilful inquirers, Martin Barry, Henle, Vogt, Kölliker, Wharton Jones, Gulliver, beset with contradictions and involved in a considerable degree of uncertainty. Nor have these difficulties been diminished by connecting with the relation between the nucleated cells and the corpuscula, the question regarding the formation of the latter.
One of the great sources of difficulty in the inquiry is this, that the corpuscula of Man and the Mammalia, though similar in several circumstances to those of the lower vertebrated and the Aspondylous animals, do not present complete resemblance to them.
According to the observations of Mr Wharton Jones, the blood of Fishes, that is, of the lower vertebrated animals, presents three kinds of cells, 1st, the granule blood-cell, containing a nucleus not at first visible, but discovered to be so by addition of acetic acid, which dissolves the granules and renders the nucleus evident; and, 2d, The nucleated blood-cell, which is the red oval corpusculum, but with the nucleus cell-form; and 3d, The pale or colourless granule cell. It appears further, that between the granule blood-cell and the nucleated blood-cell there subsists this relation, that they form two different phases of development of the same body; the granule cell being the early stage, and the nucleated cell the second or more advanced. It seems also probable, from the observations of the same inquirer, that the pale or colourless granule cells mentioned as the third kind, form advanced stages of the dark looking granule cell.
In the blood of the frog, which is taken as the representative of the reptile family, there are recognised two forms of corpuscula: 1. Granule cells in coarse and fine granular stages; and, 2. Nucleated cells in colourless and coloured stages. The nucleated blood cell in its coloured stage is the red oval corpuscle of the blood of the frog, that is, the blood globule of the frog in its most complete form.
Regarding the blood corpusculum of the Mammalia and Man, it appears to be certain that the central spot does not correspond to the nucleus, though this has been imagined by some observers.
In all the vertebrated animals hitherto examined, Oviparous and Mamiferous, there are, first, blood corpuscula in the first stage of development, or presenting the phase of Granule Cell, either coarsely grained or finely granular. Secondly, in all the animals examined there are blood corpuscula, in the second stage of development, that is in the phase of Nucleated Cell, which may be a in the colourless stage, or b in the coloured stage.
Regarding the nucleated blood-cell in the coloured stage, this occurs in its highest degree of development, and in great numbers, only in the Oviparous Vertebrata, in which it constitutes the red corpusculum, and in the early mamiferous embryo. In the fully formed blood of the Mammalia it occurs in a comparatively low degree of development, and in very small number.
---
1 Allgemeine Anatomie, Seite 193, 194, 198. In the Mammalia alone is the blood corpusculum found in what Mr W. Jones calls the third stage of development, or the phase of free cell-form nucleus. This is found in both uncoloured and coloured stages. In the former stage it is rare; in the latter it is the red corpuscle of the fully formed blood of man and the mammalia. In short, it is the opinion of Mr Jones, that the red corpusculum or globule of the fully formed blood of man and the mammalia is the cell-form Nucleus of the nucleated cell set free by the bursting of this cell itself, and become filled and red by the secretion of globuline and colouring matter into its interior.
For the facts and arguments establishing this inference, we refer to the memoirs of Mr Wharton Jones.¹
CHAP. II.—THE COMMON TISSUES.
Filamentous or Cellular Tissue. (Tela Cellulosa.—Tissu Cellulaire.—Tissu Mugueux de Borden.—Corpus Cribrosum Hippocratis.—Corps Cribleux de Fouquet.—Reticular Membrane of William Hunter.) Das Bindegewebe of Müller and Henle.
Under the name of Connecting Tissue, Henle describes a tissue consisting in its final elements of long, very fine, soft, transparent filaments, or cylinders or fibrils of uniform strength, and of a diameter varying from 0.0003-0.0008 of one line. This tissue he distinguishes into two general forms; one the shapeless or unformed Connecting Web; the other the formed Connecting Web. The first of these corresponds to what has been described by various authors under the names of Cellular Tissue, Mucous Tissue, and Filamentous Tissue. Under the second, which he divides into two orders, the Non-contractile and the Contractile Joining Web, he arranges a great number of textures in the following manner:—I. Non-contractile formed Web, including, 1. Tendon; 2. Ligament; 3. Fibrous Sheaths; 4. Fibrous Membranes, as the fibrous covering of the Corpora Cavernosa and the Dura Mater, the Membrana Tympani, the Valves of the veins, the Neurilema, the Fascia, the Periosteum, and the Perichondrium; 5. The Tunica Nervosa of the intestinal canal; 6. The External Coat of the Bloodvessels; 7. The Serous Membranes; 8. The Pia Mater and the Choroid Membrane;—II. Formed Contractile Joining Web, including the Skin; the Dartos; the Investing membrane of the Corpora Cavernosa; and the Contractile Web of the longitudinal and annular coat of the veins and lymphatic vessels.
Without pretending to offer any opinion upon the propriety of arranging all these different tissues under the head of Connecting Web, it may be remarked, that it is not very easy in this manner to communicate correct ideas of the true anatomical and physical characters of these tissues; and as the method already adopted in this article possesses the advantage of being at once simple, free from hypothesis, and serviceable to readers, it seems more prudent to adhere to it, after the explanations now given.
The general distribution of the filamentous or cellular tissue was first maintained by Haller and Charles Augustus de Bergen, and afterwards made the subject of elaborate discussion by William Hunter and Borden. It may be described as a substance consisting of very minute thready lines, which follow no uniform or invariable direction, but which, when gently raised by the forceps, present the appearance of a confused and irregular network. As these minute lines cross each other, they form between them spaces of a figure not easily determined, and perhaps not uniform. By some authors these spaces or intervals have been named cells; but, accurately speaking, the term is not fortunately applied. The component lines, which do not exceed the size General of the silkworm threads, are so slender, that they do not form those distinct partitions which the term cell implies; and though by forcible distension, such as takes place in insufflation, or separation by forceps, cavities appear to be formed, these, it will be found, are artificial, and result from the separation of an infinity of the slender filaments of which the part is composed. These interlinear spaces necessarily communicate on every side with each other; and indeed the most distinct way of forming a true idea of the structure of the cellular tissue, is to suppose a certain space of the animal body which is divided and intersected into an infinite multitude of minute spaces (areole) by slender thready lines crossing each other. This description, derived from personal observation, renders the name of filamentous more appropriate to this tissue than that of cellular by which it is generally known.
The interstitial spaces resulting from the interlacement of these filaments do not exist as distinct cavities in the healthy state, so that they cannot be said to contain any substance solid or fluid. But when an incision is made into this tissue in the living body, it is found, that if we except those fluids which issue from divided vessels, nothing is observed to escape but a thin exhalation or vapour, which is evidently of an aqueous nature. This is what some authors have termed, from its resemblance to the serous part of the blood, the cellular serosity (Bichat), and the quantity of which has been greatly exaggerated. In the living body it appears not to exist as a distinct fluid, but merely as a thin vapour, which communicates to the tissue the moist appearance which it possesses.
This fluid is understood to be derived from the minute colourless capillaries named exhalants; and it is supposed to be no sooner poured forth in an insensible manner, than it is removed by the absorbing power of lymphatics, minute veins or both. It is further believed, that whatever serous fluid is secreted into the interstitial spaces or cells of the filamentous tissue, is in the healthy state speedily removed; so that exhalation implies absorption; and the filamentous tissue is therefore represented as the seat of incessant exhalation and absorption.
The serous fluid of the filamentous tissue varies in quantity in different regions. In the cellular tissue of those parts which are free from fat, as in the eyelids, the prepuce, the nymphae and labia, and the scrotum, it is said to be more abundant than in others. The peculiar structure of those parts, which is cellular, may render any excess of serous fluid more conspicuous; for it is matter of observation, that in many persons otherwise healthy these parts are not unfrequently distended with serous fluid. On the other hand, it must be remarked that the submucous cellular tissue, and that which surrounds arteries, veins, and excreting ducts, which is delicate in substance and compact in structure, contains but a small proportion of serous fluid, and does not readily admit its presence.
This fluid has been generally said to be of an albuminous nature; and if it be identical with the serum of the blood, from which it is believed to be secreted, this character is not unjustly given it. Bichat, who maintained this opinion, injected alcohol into the filamentous tissue of an animal previously rendered emphysematosus, and found in various parts whitish flocculi, which he regarded as coagulated albumen. He also obtained the same result by immersing a portion of the scrotum in weak nitric acid; and when a considerable quantity of this tissue was boiled, it furnished much whitish foam, which Bichat regarded as albuminous.² These ex-
¹ Philosophical Transactions of the Royal Society of London for the year 1846, Part II., and Edinburgh Medical and Surgical Journal, vol. sixty-third, 1847, p. 529, and vol. seventy-third, 1850, p. 395. ² Anatome Genitale, tom. I. p. 50. General periments, however, are liable to this objection, that the effects in question may have arisen from coagulation of part of the filamentous tissue itself, which contains a considerable proportion of albuminous matter. The best mode of determining the point is to obtain the fluid apart, and to try the effects of the usual tests on it when isolated from the tissue in which it is lodged.
The description here given applies to the proper filamentous tissue. This substance was shown by Ruysch, and afterwards by William Hunter and Mascagni, to be penetrated by arteries and veins. Exhalants, absorbents, and nerves, it is also said to receive. The arteries certainly belong in the healthy state to the order of colourless capillaries, which are nearly the same with exhalants. It does not appear that the nervous twigs observed to pass through this tissue are lost in it; for in general they have been traced to some contiguous part.
Such are the general properties of this tissue, considered as an elementary organic substance extensively diffused through the body. In particular regions it undergoes some modifications, which may be referred to the following heads:
1. Beneath the skin, or rather under the adipose membrane,—the subcutaneous and intermuscular cellular tissue; 2. Beneath the villous or mucous membranes,—the submucous cellular tissue; 3. Beneath the serous membranes,—the subserous cellular tissue; 4. Round bloodvessels, excreting ducts, and other organs,—the inclosing tissue, vascular sheaths, &c.; 5. In the substance of organs,—the penetrating cellular tissue.
The situation of the subcutaneous filamentous tissue deserves particular notice. Though generally represented as below the skin, it is not immediately under this membranous covering. The skin rests on the adipose membrane, beneath which again is placed the filamentous tissue, extending like a web over the muscles and bloodvessels, penetrating between the fibres and bundles of the former, surrounding the tendons and ligaments, and connected by these productions with a deep-seated layer, on which the muscles move, where they do not adhere to the periosteum and to bones.
The extensive distribution of the subcutaneous filamentous tissue, the mutual connection of its parts, and its ready communication with the filamentous tissue of the mucous and serous membranes, were demonstrated by Haller, William Hunter, and Bordeu, and have been clearly explained by Portal and Bichat. The principal points worthy of attention may be stated in the following manner.
The filamentous tissues of the head and face communicate freely with each other, and with that of the brain by the cranial openings, and with the submucous tissue of the eyelids, nostrils, lips, and the inner surface of the mouth and cheeks. It communicates also with the subcutaneous tissue of the neck all round; and at the angle of the jaw, in the vicinity of the parotid gland, is the common point of reunion. To this anatomical fact is referred the frequency of swellings and purulent collections in the region of the parotid in the course of the various diseases of the head, face, and neck.
The filamentous tissue of the neck may be viewed as the connecting medium between that of the head and trunk. From the former region it may be traced downwards along the back, loins, breast, sides, flanks, and belly. At the cervical region, and between the shoulders, it is dense and abundant; and, surrounding the dorsal part of the vertebral column, it is connected with the mediastinal tissue, the submucous tissue of the lungs, and the subserous tissue of the costal pleura. At the fore part of the neck it is in like manner connected with the abundant tissue of the pectoral region, and by means of that surrounding the larynx and trachea, last, with the submucous tissue of the bronchi; and, General Anatomy, 2d, with the anterior mediastinum. Passing downwards, the same communication may be traced with the intermuscular tissue of the loins and belly, the tissue surrounding the lumbar and sacral portion of the vertebral column, that connecting the mesentery and large vessels to the vertebrae, and extending all round under the muscular peritoneum, and into the pelvis, where, by means of the tissue at the posterior surface of the abdominal muscles, at the anterior surface of the iliacus internus, and through the obturator hole and ischiadic notch, it communicates with the filamentous tissue of the lower extremities. From the rectum and branches of the ischium it is continued along the perineum by the urethra, and into the scrotum.
In the whole of this course, it is abundant in the space before the vertebrae, round the psoas and iliacus internus muscles, and round the bladder, rectum, prostate gland, and womb. The tissue surrounding the vertebral column communicates with that in the interior of the column by the intervertebral holes.
The armpit may be considered as the point of union between the filamentous tissue of the trunk and that of the upper extremities, while the groin is the corresponding spot for the lower extremities. These facts should be kept in mind in observing the phenomena of diseases of this tissue.
Notwithstanding this general connection, however, certain parts of the tissue are so dense and close as to diminish greatly the facility of communication. Thus, along the median line it is so firm, that air injected invariably stops, unless impelled by a force adequate to tear open its filaments; and water is rarely found effused in this situation. In the neighbourhood of some parts of the skeleton also, as at the crest of the ilium, over the great trochanter, and on the shin, the filamentous tissue is very dense and coherent.
In chemical composition it consists principally of gelatine, but contains some albuminous matter.
Adipose Tissue. (Tela Adiposa.—Tissu Adipeux.—Tissu Graisseux.) Fett-Gewebe (Henle).
The separate existence of an adipose membrane was suspected by Malpighi, maintained by De Bergen and Morgagni, and demonstrated by William Hunter. It was however, confounded with the filamentous tissue, under the general name of cellular membrane, adipose membrane, and cellular fat, by Winslow, Portal, Bichat, and most of the continental anatomists, till distinguished and described by M. Beclard.
According to the dissections of De Bergen and Morgagni, the demonstrations of Hunter, and the observations of Beclard, its structure consists of rounded packets or parcels separated from each other by furrows of various depth, of a figure irregularly oval, or rather spheroidal, varying in diameter from a line to half an inch, according to the degree of corpulence and the part submitted to examination. Each packet is composed of small spheroidal particles, which may be easily separated by dissection, and which are said to consist of a cluster of vesicles still more minute, and agglomerated together by delicate cellular tissue. The appearance of these ultimate vesicles is minutely described by Wolff in the subcutaneous fat, and by Clopton Havers and Monro, in the marrow of bones, in which the last two authors compared them to strings of minute pearls. If the fat with which these vesicles are distended should disappear, as happens in dropsy, the vesicles collapse, their cavity is obliterated, and they are confounded with the contiguous cellular tissue, without leaving any trace of their existence.
Hunter, however, asserts, that in such circumstances the cellular tissue differs from the tissue of adipose vesicles, in containing no similar cavities; and justly remarks that the latter is much more fleshy and ligamentous than the filamentous tissue, and contends, that though the adipose receptacles are empty and collapsed, they still exist. When the skin is dissected from the adipose membrane it is always possible to distinguish the latter from the filamentous tissue, even if it contain no fat by the toughness of its fibres, and the coarseness of the web which they make.
The distinguishing characters between the cellular or filamentous and the adipose tissue may be stated in the following manner.—1st, The vesicles of the adipose membrane are closed all round, and, unlike cellular tissue, they cannot be generally penetrated by fluids which are made to enter them. If the temperature of a portion of adipose membrane be raised by means of warm water to the liquefying point of the contents, they will remain unmoved so long as the structure of the vesicles is not injured by the heat. If, again, an adipose packet be exposed to a heat of +40 centigr. =104° F., though the fat be completely liquefied, not a drop escapes until the vesicles are divided or otherwise opened, when it appears in abundance. The adipose matter, therefore, though fluid or semifluid in the living body, does not, like dropsical infiltration, obey the impulse of gravity. 2d, The adipose vesicles do not form, like cellular tissue, a continuous whole, but are simply in mutual contiguity. This arrangement is demonstrated by actual inspection, but becomes more conspicuous in the case of dropsical effusions, when the filamentous tissue interposed between the adipose molecules is completely infiltrated, while the latter are entirely unaffected. 3d, The anatomical situation of the adipose tissue is different from that of the filamentous tissue. The former is found, 1st, in a considerable layer immediately beneath the skin; 2d, between the peritoneal folds which form the omentum and mesentery; 3d, between the serous and muscular tissues of the heart; and, 4th, round each kidney.
In each of these situations it varies in quantity and in physical properties. In the least corpulent persons a portion of fat is deposited in the adipose membrane of the cheeks, orbits, palms of the hand, soles of the feet, pulp of the fingers and toes, flexures of the joints, round the kidney, beneath the cardiac serous membrane, and between the layers of the mesentery and omentum. In the more corpulent, and chiefly in females, it is found not merely in these situations, but extended in a layer of some thickness almost uniformly over the whole person; and is very abundant in the neck, breasts, belly, mons veneris, and flexures of the joints.
Besides the delicate cellular tissue by which the packets and vesicles are united, the adipose tissue receives arterial and venous branches, the arrangement of which has been described by various authors, from Malpighi, who gave the first accurate account, to Mascagni, to whom we are indebted for the most recent. According to the latter, who delineates these vessels, the furrow or space between each packet contains an artery and vein, which, being sub-divided, penetrate between the minute grains or particles of which the packet is composed, and furnish each with a small artery and vein. The effect of this arrangement is, that each individual grain or adipose particle is supported by its artery and vein as by a foot-stalk or peduncle, and that those of the same packet are kept together, not only by contact, but by the community of ramifications from the same vessel. These grains are so closely attached, that Mascagni, who examined them with a good lens, compares them to a cluster of fish-spawn. Grutzmacher found much the same arrangement in the grains and vesicles of the marrow of bones.
It has been supposed that the adipose tissue receives nervous filaments; and Mascagni conceives he has demonstrated its lymphatics. Both points, however, are so problematical, that of neither of these tissues is the distribution known.
The substance contained in these vesicles is entirely inorganic. Always solid in the dead body, it has been represented as fluid during life by Winslow, Haller, Portal, Bichat, and most authors on anatomy. The last writer indeed states, that under the skin it is more consistent, and that in various living animals he never found it so fluid as is represented. The truth is, that in the human body, and in most mammiferous animals during life, the fat is neither fluid nor semifluid. It is simply soft, yielding, and compressible, with a slight degree of transparency or rather translucence. This is easily established by observing it during incisions through the adipose membrane, either in the human body or in the lower animals.
The properties and composition of fat form a subject for chemical rather than anatomical inquiry; and in this respect its nature has been particularly investigated by M. Chevreul. According to the researches of this chemist, fat consists essentially of two proximate principles, stearine (στερα, sebum, sappo), and elaine (ελαιον, oleum). The former is a solid substance, colourless, tasteless, and almost inodorous, soluble in alcohol and ether, and preserving its solidity at a temperature of 138° F., but fusible between 140° and 145° F. Elaine, on the contrary, though colourless, or at most of a yellow tint, and lighter than water, is fluid at a temperature of from 17° to 18° centigrade, =63° to 64° F., and is greatly more soluble in alcohol.
Of this substance marrow appears to be merely a modification; and the membranous cavities or medullary membrane in which it is contained may be viewed as an intraosseous adipose tissue.
Little doubt can be entertained that animal fat is the result of a process of secretion; but it is no easy matter to determine the mode in which this is effected. Malpighi, departing, however, from strict observation, imagined a set of ducts issuing from glands, in which he conceived the fat to be elaborated and prepared. To this he appears to have been led by his study of the lymphatic glands, and inability to comprehend how the process of secretion could be performed by arteries only. This doctrine, however, was overthrown by the strong arguments which Ruysch derived from his injections; and Malpighi himself afterwards acknowledged its weakness and renounced it. In short, neither the glands nor the ducts of the adipose membrane have ever been seen.
Winslow, though willing to adopt the notion of Malpighi, admits, however, that the particular organ by which the fat is separated from the blood is unknown. Haller, on the contrary, aware of the permeability of the arteries, and their direct communication with the cells of the adipose tissue, and trusting to the testimony of Malpighi, Ruysch, Glisson, and Morgagni, that it existed in the arterial blood, saw no difficulty in the notion of secretion, or rather of a process of separation; and upon much the same grounds the opinion is adopted by Portal and others. Bichat, again, contends that no fat can be recognised in the arterial blood, and reduces the fact, that none can be distinguished in blood drawn from the temporal artery.
All this, however, is more or less erroneous. It has been ascertained by Babington, Gmelin, Denis, Boudet, and Lecanu, that fat or oil exists in blood in the normal state; and there is no difficulty in understanding that from this fluid it must be secreted and deposited in the adipose tissue. The truth is, that fatty matter is found in the chyle, and is conveyed into the blood by the chyliferous vessels; and that it is found in the blood after meals of certain kinds of food, has been shown by the researches of Dr R. D. Thomson and others. From these facts, it may be inferred, that adipose matter or its elements are conveyed in minute quantities into the blood, and that the fat itself is deposited from the vessels in various parts of the adipose tissue, and in the medullary membrane of the bones, in which it is afterwards found. From the phenomena of various diseases, and from those manifested by hibernating animals, which retire in the beginning of winter fat and heavy, and come out in spring meagre and emaciated, there is reason to believe that fat is absorbed by the veins and lymphatics.
There is little difficulty in understanding the sources from which fat is derived in animal bodies. All amylaceous and saccharine articles of food furnish the elements of fat; and it is impossible to doubt that from these chiefly, together with the oils found in the seeds and other parts of vegetables, fat may be formed. In animals which live almost entirely on grass and the seeds of grassy vegetables, as the ox, sheep, horse, deer, and camel, the amylaceous and saccharine matters of their food are manifestly converted into fat and marrow.
Insects abound in fat; and in the bee this substance is prepared from sugar.
**Artery, Arterial Tissue. (Arteria,—Tissu Arteriel.)**
Most anatomical writers, previous to the time of Henle, distinguished in the arterial tissue three tunics; 1st, an internal; 2d, a middle or fibrous coat, consisting of annular fibres; and 3d, an external or common covering of condensed filamentous tissue.
Henle enumerates six different tunics; 1st, the first or inner coat, consisting of pavement epithelium; 2d, the striped or trellised coat; 3d, the longitudinal fibrous coat; 4th, the annular fibrous coat; 5th, an elastic tissue found only in arteries of large calibre; and 6th, the external, filamentous, or adventitious coat.
Of these six tissues, the first three correspond to the inner coat; the fourth is the ordinary fibrous or elastic coat of arteries; the fifth is not present in all vessels; and the sixth is the ordinary external coat of filamentous tissue.
The Epithelial coat is seen in the smallest vessels as a simple granular membrane in which the cell-nuclei only are deposited in a certain order. Frequently it has quite the same structure as the Epithelium of the Serous Membranes; in other instances the nuclei are oval, the cells extremely pale, and so flat, that those standing on the edge appear as thin filaments, something swollen in the centre, the region of the nucleus. Henle allows that this arterial epidermis may be wanting or transformed into the next tissue.
The second layer, the Striped or Trellised coat, is a very fine, transparent, moderately stiff, brittle membrane, the filaments of which divericate and decussate each other.
The third layer, the best specimens of which are seen in the valves of the veins, belongs only doubtfully to the arterial tissue.
The two first-mentioned tissues correspond to the inner coat described below.
Every arterial tube greater than one line in diameter is visibly composed of one adventitious and two essential substances: the first, the sheath, reputed to consist of condensed filamentous tissue; the last two, the proper arterial and internal tissues. (Tunica propria et membrana intima.)
1. The inner surface of the arterial tube is formed by a very thin semitransparent polished membrane, which is said to extend not only in the one direction over the inner surface of the left ventricle, auricle, and pulmonary veins, but in the other to form the minute vascular terminations which are distributed through the substance of the different organs. This membrane is particularly described by Bichat under the name of common membrane of the system of red blood, because he believed it to exist wherever red blood was moving,—in the pulmonary veins, in the left side of the heart, and over the entire arterial system.
The inner membrane may be demonstrated by cutting open or inverting any artery of moderate size, when it may be peeled off in the form of thin slips by the forceps. Or, if the tube be fitted on a glass rod, by removing the layers of the proper membrane in successive portions, the inner one at length comes into view in the form of a thin translucent pellicle, of uniform, homogeneous aspect, without fibres or other obvious traces of organization. Under the microscope, however, if we can trust the descriptions of Henle, this coat appears to be composed of the filaments above mentioned. These filaments cannot be said, strictly speaking, either to be transverse or longitudinal in relation to the axis of the artery. Most of them are rather oblique; and they ramify at acute angles, and form anastomotic unions with each other. The stripes formed by these filaments are extremely pale and difficult to be seen. Henle further mentions as scattered between the fibres, holes variable in size, mostly round in shape, but here and there regularly broad, as if the effect of laceration.
This membrane is supposed to be prolonged to form those minute vessels in which the proper coat cannot be traced. It is very brittle, and is distinguished during life by a remarkable activity in forming the morbid states to which arteries are liable. In other respects it is deemed by Bichat peculiar, and, though similar to the proper membrane, is to be considered as unlike any other tissue. Its chemical composition is not known.
2. Exterior to this common or inner membrane is placed a dense strong tissue of considerable thickness, of a dun yellowish colour, which is found to consist of fibres disposed in concentric circles placed contiguous to each other round the axis of the artery. If this substance be examined either from without or in the opposite direction, it will be found that, by proper use of forceps, its fibres can be separated to an indefinite degree of minuteness, even to that of a hair, and that they uniformly separate in the same direction. Longitudinal fibres are visible neither in this nor any other tissue of the arterial tube. This is the proper arterial tissue; (tunica propria.) Its uniform dun yellow colour is perceived through the semitransparent inner membrane, and is most conspicuous either when this is removed, or when the outer cellular envelope is detached and the component threads separated from each other; and if it be less distinct in the smaller branches, it is because the tissue on which the colour depends is here considerably thinner. In this respect it varies in different regions. Though in general less dense and abundant as the arteries recede from the heart, it is thicker, ceteris paribus, in those of the lower than in those of the upper extremities. In the vertebral and internal carotid arteries, and in those distributed in the substance of the liver, spleen, &c., it is thinner than in vessels of the same size in the muscular interstices.
This is the tunic which Henle calls the Annular Coat. His description includes both this proper or middle coat of the Arteries and the proper coat of the Veins, and has thereby been made less appropriate than it might otherwise have been. He describes the arterial annular coat as presenting fine dark streaks, or rows of dark-coloured punctula, running across the axis of the artery; and he thinks it certain that these streaks proceed from the original transverse oval Nueléi, and that therefore they give distinct evidence of the mode in which the annular coat is developed.
In acetic acid the annular arterial coat is resolved into fine vessels, so that the transversely oval nuclei float about free in the mass. The peculiar fibres of the middle arterial coat become by acetic acid pale, transparent, yet not dissolved. The dark stripes and punctula remain unchanged.
In rare instances the proper fibres of the middle arterial coat are curled as fasciculi of fibro-filamentous tissue.
Henle maintains that no proper filamentous tissue is found in the annular coat, not even to connect the separate layers of the coat, though this is frequently asserted. He has occasionally met with shreds of the trellised coat itself in the external layer of the annular coat. Räuschel saw on all fine sections of the aorta, the layers of the proper fibres separated by means of transparent fine partitions, which consequently must perforate the proper fibres in all directions. If the middle coat be stripped from an artery, after it has been treated with wood vinegar, and again softened in water, it is easily divided into layers which are not separated by fibres, but by a white, fibreless transparent substance. Portions of this are sometimes attached to the transverse fibres. Henle thinks, in short, that the trellised coat forms not only the internal layer of the annular coat, but also separates the component layers of that coat. Räuschel counted in the aorta forty-four layers, in the carotid artery twenty-eight, in the axillary artery fifteen layers, separated by similar partitions. In the other arteries, these must be wanting.
The nature of this tissue has been the subject of much controversy. It was long believed to be muscular, and to possess the properties of muscular fibre. Bichat showed that the arguments by which this opinion was supported are inconclusive, and that the arterial tissue has very few qualities in common with the muscular. The circumstances from which he derived his proofs were its physical and physiological properties.
The arguments derived from the physical properties of this tissue are chiefly the following:—The arterial tissue is close, elastic, fragile, and easily divided by ligature; muscular fibre is more loose in structure, by no means elastic; and, instead of being divided or cut by ligature as artery is, undergoes a sort of strangulation. The action of alcohol, diluted acids, and caloric, by means of hot fluids which are not corrosive, affords a proof of the chemical difference of these animal substances. All of them produce in the arterial tunic a species of shrivelling or crisping, which seems to depend on more complete coagulation of one of the chemical principles; but no similar effect takes place in muscular fibres. According to Berzelius, the proper arterial tunic contains no fibrin.1 Beclard, however, asserts that he has ascertained that it contains a portion of this principle; but nevertheless hesitates to consider it as a muscular or fibrous tissue, and expresses his opinion that it would be with greater propriety referred to that order of substances which he has named yellow or tawny fibrous system.
The consideration of the physiological or organic properties leads to similar results. Neither mechanical nor chemical agents applied as stimulants produce any change or motion in the living arterial membrane. 1. The arteries of an amputated limb, exposed the moment after amputation, while the muscles are in active motion, do not contract or move when punctured by the scalpel. 2. The experiments of Bicker and Van-den-Bos with the electric spark, and those of Vassalli-Emidi, Ginilio, and Rossi with the galvanic pile, may be considered as disproved by the experiments of Nysten,2 who found no contraction in the human aorta after violent death, while the heart and other muscles could still be excited. In performing the same experiment with the artery of the living dog, this physiologist was equally disappointed. 3. The circular contraction of the calibre of an artery either partially or wholly divided, depends not on irritability, but either on its elasticity, or on that property which it possesses of contracting strongly the instant the distending agent is removed. This power is different from muscular contraction or irritability, and must not be confounded with them; but it depends on the living state of the body and the individual arterial tube. 4. The contraction said to take place in living arteries after the application of alcohol, acids, or alkalies, is to be ascribed to the chemical crisping, and not to stimulant power. It does not relax. 5. These inferences are not inconsistent with the experiments of Thomson, Philips, Hastings, Wedemeyer, and Kaltenbrunner, on minute arterial tubes, which may be admitted to possess something like irritability, or rather susceptibility of contraction, without the necessity of supposing the same property in the large branches and trunks. 6. This is so much more probable, as in these minute arteries the proper arterial tunic is either wanting, or is so much thinner and so modified, that it is impossible to conceive its presence capable of affecting the result of experiments made to determine the degree or kind of arterial contraction.
On the other hand, Henle maintains that the outer layers of the annular coat are muscular, and belong to the same category to which are referred the muscular fibres of the intestinal canal and those of excretory ducts.2
3. The outer surface of the proper arterial tissue is enveloped, as above noticed, in a layer of dense filamentous or cellular membrane, which is very firmly attached to it, and which was formerly considered as part of the arterial tissue. It is adventitious; a modification of filamentous or cellular texture, which establishes a communication between the artery and the contiguous parts, and is necessary to the nutrition and healthy state of the vessel. It incloses and transmits the minute vessels anciently denominated vasa rerorum (arteriola arteriarum, Haller); and if detached even through a trifling extent, the arterial portion thus divided is sure to become dead, to be affected with inflammatory and sloughing action, and ultimately to give way and discharge the contents of the vessel. M. Beclard considers it a fibro-cellular membrane, which may in the larger arteries be divided into two layers; one exterior, similar to the general filamentous tissue; the other inside, between the outer layer and the proper tissue, yellowish and firm, but still sufficiently distinct from the proper tunic. In the cerebral arteries it is wanting, and in most parts of the chest and belly its absence is supplied by a portion of pericardium, pleura, or peritoneum. Yet even there a thin layer of fine cellular tissue appears to connect these membranes to the proper tunic. In the extremities the cellular sheath is removed in dissecting arterial preparations.
The internal filamentous tissue above-mentioned is what Henle calls the fifth arterial coat. It occurs only in arteries of large size. It is a coat of true elastic tissue; a white membrane, which can be rent into fibres neither transversely nor longitudinally, but always follows the tug of the forceps in small shreds. This membrane possesses the firmness of the elastic tissue, while the annular coat is slender and brittle. When treated with acetic acid, this membrane retains completely its white colour, while the annular coat becomes transparent; though thinner, it has a much greater degree of elasticity than the annular coat; and it possesses the microscopical character of the elastic tissue in a remarkable degree.
At different periods several anatomists, as Willis, Douglas and Delasone, have maintained the existence of longitudinal fibres in arterial tissue; and even at the present day this no-
---
1 A View of the Progress of Animal Chemistry, by J. J. Berzelius, M.D. &c. &c., p. 24, 25. London, 1813. 2 Nouvelles Expériences Galvaniques, &c., par P. H. Nysten, &c., l'an 11, p. 235-6. Paris. Recherches de Physiologie, 1811, p. 307. Paris. 3 Adversaria Anatomica, tom. ii. p. 78. General tions is not entirely abandoned. Morgagni was the first who, Anatomy, trusting to mere observation, doubted the existence of these fibres, and stated that he was unable to perceive them. Upon the same ground Haller would not admit of their existence; and Bichat and Meckel positively denied them. The longitudinal filaments mentioned by Henle are found principally in the veins.
Though arterial tissue does not appear to be very vascular, it is furnished with arteries and veins (easae vasa- rum, arteriae arteriarum), which do not come from the artery or vein itself, but from the neighbouring vessels. Thus the aorta at its origin is supplied with minute arteries from the right and left coronary, and in some instances with a proper vessel adjoining to the orifice of the right coronary artery, which Haller regards as a third coronary. The rest of the thoracic aorta derives its vessels from the upper bronchials, from twigs of the internal mammary arteries, from the bronchials, from the cesophageals, and from the phrenics. The abdominal portion is supplied from the spermatics, the lumbar, and in some instances the mesocolic artery. The same arrangement nearly is observed with regard to the veins.
Few textures are more liberally supplied with nerves than arteries are. Almost every considerable trunk or vessel is surrounded by numerous plexiform filaments of nerves, many of which may be traced into the tissue of the artery. The anterior part of the arch of the aorta is abundantly supplied with branches from the superficial cardiac nerves, which Haller was unable to trace beyond the artery. The celiac, the mesenteric, and the mesocolic arteries are invested with numerous plexiform nervous filaments derived from the large semilunar ganglion of the splanchnic nerve. The renal arteries in like manner are surrounded by numerous twigs of the renal plexus; and each of the intercostal arteries at its origin receives nervous threads from the intercostal nerves. This arrangement, which is observed chiefly in the blood-vessels going to the internal organs, led Bichat to announce it as a general fact, that the arteries derive their nerves almost exclusively from the ganglions and the ganglial nerves. The inference does not rest upon strict observation, and evidently owes its birth to the hypothetical opinions of this ingenious physiologist. All the arteries going to the extremities, the axillary, and iliac, and their branches, receive nerves from the neighbouring nervous trunks, which are formed chiefly from cerebral or spinal nerves, and have no immediate connection with the system of the ganglions. In the internal carotid and the vertebral arteries, and their branches, nerves cannot be distinctly traced.
Organized in the manner now described, it is requisite to take a short view of the anatomical connections of the arterial system, or to consider it in its origin, its course, and its termination.
The arterial system of the animal body may be viewed as one large trunk divided into several branches, which again are subdivided and ramified to a degree of minuteness which exceeds all calculation. It is requisite, therefore, to consider the origin, 1st, of the aorta, the large trunk; 2dly, of the branches which arise from it; and, 3dly, of the small vessels into which these are divided.
Every one knows that the aorta is connected at its origin with the upper and anterior part of the left ventricle. The manner of this connection has been well examined by Lancisi, by Ludwig, and particularly by Bichat. It may be demonstrated by dissection, but is much more distinctly shown by boiling the heart with the blood-vessels attached. In a heart so treated, the thin internal membrane may be traced passing from the interior of the ventricle along the margin of its orifice to the inside of the arterial tube. Exactly at the point of union it is doubled into three semicircular folds, forming semilunar valves, and thence is continued along the whole course of the artery. This membrane is entirely distinct from the proper or fibrous coat. Of the latter, the cardiac extremity or beginning is notched into three semicircular sections, each of which corresponds to the base or attached margin of a semilunar valve. These sections are attached to the aortic orifice of the ventricle by delicate filamentous tissue, but are not connected with the fleshy fibres of the heart; and at the angle or point of attachment the thin inner membrane is folded in so as to fill up a space or interval which is left between the margin of the orifice and the circumference of the proper arterial tissue, where it is notched or trisected.
The aorta is soon divided into branches, which again are subdivided into small vessels. With the mathematical physiologists it was a favourite problem to ascertain the number of branches into which any vessel might be subdivided. Keill made them from forty to fifty. Haller states that, counting the minutest ramifications, he has found scarcely twenty. The inquiry is vain, and cannot be subjected to accurate calculation. In no two subjects is the same artery found to be subdivided the same number of times; and in no two subjects are the same branches found to arise from the same trunk.
A branch issuing from a trunk generally forms with it a particular angle. Most generally, perhaps, these angles are acute; but in particular situations they approach nearly to a right angle. Thus the innominate, left carotid, and left subclavian, issue from the arch of the aorta nearly at a right angle, at least to the tangent of the arch. The intercostals form a right angle with the thoracic aorta; the renal and lumbar arteries form a large acute angle, approaching to right, with the abdominal; and the celiac comes off nearly in the same manner from the anterior part of the vessel. The internal and external carotids, again, the external and internal iliacs, the branches of the humeral, and those of the femoral, form angles more or less acute with each other. The angle which the spermatics make is, generally speaking, the most acute in the arterial system.
I have already alluded to the structure of the arterial tissue at the divarications. These changes relate both to the inner and to the proper membrane. In the inside of the vessel the inner membrane is folded somewhat so as to form a prominent or elevated point, the disposition of which varies according to the angle of divarication. 1st, When this is rectangular, the prominence of the inner membrane is circular, and is equally distinct all round. 2d, When the angle is obtuse, as in the mesenteric artery, the prominence is distinct, and resembles a semicircular ridge between the continuation of the trunk and the branch given off, but indistinct on the opposite side where the angle is obtuse. 3d, If the angle is acute, and that
---
1 Allgemeine Anatomie, seite 575. 2 "Verum anatome et microscopium omnino fibras longitudinem sequentes nunquam demonstravit, aut mihi, aut aliis ante me scriptoribus, quorum auctoritate meam teor." (Elementa Physiologica, lib. ii. sect. 1, § 7.) 3 Hunter, sect. iv. p. 131. 4 Le grand arbre à sang rouge ou l'artériel est presque exclusivement embrassé par la première classe des nerves." (Anatomie Générale, tom. i. p. 302.) 5 H. A. Wrisberg, De Nervis Arteriarum Venarum comitantibus, apud Haller, Dissert. Anatom. Select. tom. iii. General formed by the branch with the continuation of the trunk is obtuse; the beginning of the artery presents an oblique circle, the elevated half of which is near the heart, the other more remote.
The arrangement of the fibres of the proper tissue is described by Ludwig from the divarication of the iliac arteries, and may be seen in any part of the arterial system where the vessels are large. The circular fibres separating form on each side a half-ring, from which is produced a complete ring, which incloses the smaller rings formed by the circular fibres of the vessel given off. These circular fibres proceed to the prominence of the internal membrane already described, and are arranged round it much in the same manner in which those of the large vessel surround its inner membrane. In this, however, no continuity between the rings of the large vessel and those of the small one can be recognised. The latter are inserted as it were into the former, and they are connected by the continuity of the inner membrane only.
In observing the course or transit of arterial tubes, the principal point deserving notice is the sheltered situation which they generally occupy, their tortuous course, and their mutual communications. In the extremities they are always found towards the interior or least exposed part of the limb, generally deep between muscles, and sometimes lying along bones. When they are minutely subdivided, they enter into the interior of organs, without, however, sinking at once into their intimate substance. In the muscles they are lodged between the fibres; in the brain, in the convolutions; in glands, between their component lobes. In such situations they are generally observed to be more or less tortuous in the course which they follow. On the reasons of this much difference of opinion still prevails. (Bichat and Magendie.)
In the course of the arteries, no circumstance is of greater moment than their mutual communications or inosculation (anastomoses). Of this there may be two forms, the first when two equal trunks unite, the second when a large vessel unites with a smaller one. Of the first, three varieties have been mentioned. 1st, Two equal trunks may unite at an acute angle to form one vessel. Thus, in the fetus, the ductus arteriosus and the aorta are conjoined; and the two vertebral arteries unite to form the basilar trunk. 2d, Two trunks may communicate by a transverse branch, as the two anterior cerebral arteries do in forming the anterior segment of the circle of Willis. 3d, Two trunks may, by mutual union, form an arch, from the convexity of which the minute vessels arise, as is seen in the branches of the mesenteric arteries. (Plate XXIX. fig. 4.)
The second mode of inosculation is frequent in the extremities, especially round the joints. The multiplied communications of the arterial system in these regions, though well known to anatomists, and enumerated by Haller, were first clearly and systematically explained by Scarpa, and afterwards by Cooper and Hodgson. The importance of this arrangement, in facilitating the motions of the circulation,—in obviating the effects of local impediment in any vessel or set of vessels,—and in enabling the surgeon to tie an arterial trunk when wounded, affected with aneurism or any other disease,—has been clearly established by these authors. Their researches have shown, that there is not a single vessel which may not be tied with full confidence in the powers of the collateral circulation. Even the aorta has in seventeen instances been found narrowed or obstructed in the human subject, and a ligature has been put on its abdominal portion. (Cooper.)
To ascertain the several modes in which arteries terminate has been a problem of much interest to the physiologist, and of no small difficulty to the anatomist. The General alleged terminations, as believed to be established, are minutely and elaborately enumerated by Haller, who, however, multiplied them too much according to the modern acceptation of the term.
1. The first undoubted termination of arteries is immediately in veins. It is unnecessary to adduce in support of this fact the long list of observers enumerated by Haller. It is sufficient to say that it was clearly established by the microscopical observations of Leeuwenhoek, Copper, and Baker, by Haller himself, and by Spallanzani in his beautiful experiments on the circulation of the blood.
2. The second termination which may be mentioned here is that into the colourless artery, (arteria non rubra.) This is sufficiently well established by the phenomena of injections.
3. A third termination which is supposed to exist, but of which no sensible proofs can be given, is that into colourless vessels supposed to open by minute orifices on various membranous surfaces, and therefore termed exhalants. The nature of these vessels shall be considered afterwards.
Haller admits a termination in, or communication with, lymphatic vessels, but allows that it is highly problematical. Partial communications have been traced between arteries and lymphatics by several anatomists; but the point requires to be again submitted to accurate researches.
Another mode of termination, that namely into excretory ducts, admitted by Haller, scarcely requires particular mention. So far as an artery can be said to terminate in such a manner, it would come under the head of that into exhalant vessels. Many of the proofs mentioned by Haller, however, may be shown to be examples of a morbid state of the mucous membranes of these ducts, in which their capillary vessels are disorganized.
In considering the several terminations of arteries, it is not unimportant to advert to the distribution of these vessels. Injections show that they penetrate into every texture and organ of the animal body, excepting one or two substances in which they have never yet been traced. But in different textures they are found in different degrees; and they may vary in extent even in the same texture in two different conditions. The parts which receive the largest and most numerous vascular ramifications are the brain and spinal chord, the glandular organs, the muscles voluntary and involuntary, the mucous membranes, and the skin. In bones, on the contrary, in the fibrous membranes, and their modifications, tendons, and ligaments, and in the serous membranes, few arteries are seen to penetrate; and these are generally minute, sometimes only colourless capillaries. In some textures arteries cannot be traced, though their properties indicate that they must receive vessels of some kind. Such are cartilage and the arachnoid membrane. (Ruysh and Haller.) Lastly, arteries are not found in the scarf-skin, in nails, the enamel of the teeth, the hair, nor in the membranes of the umbilical chord. In early life bones are much more vascular than in adult age; and in the bones of young subjects arteries may be traced going out through the epiphyses into the cartilages, in which they cannot at a later period of life be demonstrated. (Phil. Trans. No. 470.)
Vein, Venous Tissue. (φλαβον—Vena.—Tissu Veineux.)
The structure of the tubular canals, termed veins, has been much less examined by anatomists than that of the arteries. Some incidental observations in the writings of Willis, Glass, and Clifton Wintringham, comprise all that was published regarding them previous to the short ac- General count of Haller. Since that time they have been described Anatomy, with various degrees of minuteness and accuracy by John Hunter, Bichat, Magendie, Gordon, Marx, and Meckel. In the following account, the facts collected by these observers have been compared with the appearance and visible organization presented by veins in different parts of the human body.
Veins.
The veins are membranous tubes extending between the right side or pulmonary division of the heart and the different organs in which their minute branches are ramified.
Every venous tube greater than one line in diameter consists of three kinds of distinct substance. The outermost is a modification of the filamentous tissue (membrana cellulosa), and though less compact and less thick than the arterial filamentous envelope, is in every other respect quite similar, and is in general intimately connected with it. The innermost (membrana intima) is a smooth very thin membrane. Between these is found a tunic somewhat thicker, which is termed the proper venous tissue (tunica propria vene). The structure and aspect of this proper membrane shall be first considered.
1st. When the loose filamentous tissue in which the blood-vessels are inclosed, and the more delicate and firm layer immediately contiguous to the veins, are removed, the observer recognises a red or brown-coloured membrane, not thick or strong, but somewhat tough, which is the outer surface of the proper venous tunic. If dissected clean it is tolerably smooth; but however much so it can be made, a glass of moderate powers, or even a good eye, will perceive numerous filaments adhering to it, which appear to be the residue of the cellular envelope.
According to Bichat, parallel longitudinal fibres, forming a very thin layer, may be distinguished in the larger veins; but he admits, although they are quite real, that they are always difficult to be seen at the first glance. In the trunk of the inferior great vein (vena cava inferior), they are always seen, he observes, more distinctly than in that of the superior; and they are always more obvious in the divisions of the former than in those of the latter vessel, and also in the superficial than in the deep-seated veins. These longitudinal fibres, he asserts, are more distinct in the saphena than in the crural vein, which accompanies the artery. Lastly, he remarks, these fibres are proportionally more conspicuous in branches than in trunks. (Anatomie Générale, tom. i. p. 399.)
Notwithstanding the apparent correctness of this description, Magendie informs us he has sought in vain for the fibres of the proper venous membrane; and he remarks that, though he has observed very numerous filaments interlacing in all directions, yet these assume the longitudinal and parallel appearance only when the tube is folded longitudinally,—a disposition often seen in the larger veins.
By Meckel, on the contrary, the accuracy of the observation of Bichat is maintained. This anatomist states that he has, by the most minute dissections, assured himself that these fibres are longitudinal; but he admits that they are not uniformly present in all parts of the venous system, and that in degree and abundance they are liable to great variation. He follows Bichat also in representing these fibres as thicker and more distinct in the system of the inferior than in that of the superior cava, and in the superficial than in the deep veins.
In the inferior cava of the human subject, certainly, filaments or fibres may be recognised. But instead of being longitudinal, they may be made to assume any direction, according to the manner in which the filamentous tissue is removed. For this reason probably these fibres are to be viewed as part of the filamentous sheath. In the saphena vein of the leg oblique fibres may be seen decussating each other; but it is doubtful whether these belong to the proper venous tissue or to the filamentous covering.
The nature of this proper membrane, or venous fibre, as it is sometimes named (Bichat), is not at all known. Its great extensibility, its softness, its want of elasticity in the circular direction, or fragility, its colour and general aspect, distinguish it from the arterial tunic. It possesses some elasticity in the longitudinal direction, and is retracted vigorously when stretched. It possesses considerable resistance, or in common language is tough. The experiments of Clifton Wintringham show that it sustains a considerable weight without breaking; and that this toughness is greater in early life, or in the veins of the young subject, than at a later period. In short, it may be stated as a general fact, that venous tissue, though thinner, possesses greater elasticity and tenacity than arterial tissue. According to the experiments of the same inquirer, this property depends on that of the superior density of the venous tissue; the specific gravity of the matter of the vena cava being invariably greater than that of the aorta in the same subject, both in man and in brute animals.
From some experiments Magendie is disposed to consider it of a floridinous character. But it exhibits in the living body no proof of muscular structure or irritable power. When punctured by a sharp instrument, or exposed to the electric or galvanic action, it undergoes no change or sensible motion.
This tunic is wanting in those divisions of the venous system termed sinuses, in which its place is supplied by portions of the hard membrane (duro mea).
2dly. The inner surface of any vein which has been laid open and well washed is found to be smooth, highly polished, and of a bluish or blue-white colour. This is the inner or free surface of the inner venous membrane (membrana intima). It is exceedingly thin, much more so than the corresponding arterial membrane, much more distensible and less fragile. It bears a very tight ligature without giving way as the arterial does; but it also sustains considerable weight, which shows that it is tough and resisting. This is the membrane termed by Bichat common membrane of dark or modern blood. According to the views of this anatomist, it forms the inner or free surface, not only of all the venous twigs, branches, and trunks composing this system of vessels, but it is extended from the superior and inferior great veins over the inner surface of the right auricle and ventricle, and thence over that of the pulmonary artery and its divisions; and through this whole tract it is the same in structure and properties.
This doctrine has not yet been controverted. But perhaps it may be doubted, both with regard to the inner arterial membrane, that the inner tunic of the aorta and of the pulmonary veins is quite the same; and in regard to this inner venous membrane, whether that of the veins in general is quite the same with that of the pulmonary artery. The subject demands further research. Meanwhile strong confirmation is found in the interesting remark of Bichat, that the osseous or calcareous depositions which are common in various spots of the inner arterial
---
1 Distrilae Anatomico-physiologica de Structura atque Vita Venarum. Carolinum, 1819. 2 Experimental Inquiry on some parts of the Animal Structure. London, 1740. General membrane, and especially at the mitral and aortic valves, are never found in the inner venous membrane, or at the tricuspid valve, or in the semilunar valves of the pulmonary artery. Have these depositions been found inside the pulmonary veins, and not inside the pulmonary artery? Ossific deposit in the valves of the pulmonary artery was seen by Bransby Cooper.
The inner or common venous membrane is, however, the most extensive and the most uniform of all the venous tissues. It is the only one which is found in the substance of organs, and is present where the cellular and proper membranes are wanting. This is the case not only with venous branches and minute canals as they issue from the substance of muscles, bones, and such organs as the liver, kidneys, spleen, &c., but is also very remarkably observed with regard to the venous canals of the brain. I have already noticed the absence of the cellular and proper tissues in these tubes; and I have now to remark, that the cerebral veins consist solely of the inner membrane while in the brain or membranes, and when in the sinuses, of this inner membrane, placed between two folds of the dura mater. When the jugular vein reaches the temporoparietal sinusosity, it loses its proper membrane, while its common or inner membrane passes into the hollow of the dura mater, called sinus, and thus forms the venous canal. This fact is readily demonstrated by slitting open either the lateral or the superior longitudinal sinus, when a thin delicate membrane, quite distinct from the fibrous appearance of the dura mater, will be found to line the interior of these canals.
The inner surface of many veins presents membranous folds projecting obliquely into the cavity of the vessel. These folds, which, from their mechanical office, have been named valves (valvulae), are parabolic in shape, have two margins, an attached and free,—and two surfaces, a concave turned to the cardiac end of the vein, and a convex turned in the opposite direction. The attached margin is not straight, as may be imagined, but circular, and adheres to the inner surface of the vessel. The free margin resembles in shape an oblong parabola; and the direction of the valve is such, that a force applied to its convex surface would urge it more closely to the vein, whereas a force applied to the concave surface would either obliterate the circular area of the vessel, tear the valve from the vein, or otherwise meet with resistance.
The size of the valves is variable. In some instances they are sufficiently large to fill the canal of the vessel, and in others they are too small to produce this effect. The obliteration of the circular area of the vessel is most perfect when there are two or three at the same point. Bichat ascribed the variable state of this quality to the dilated or contracted condition of the veins at the moment of death. This, however, is denied by Magendie.
In structure these valvular or parabolic folds are said to consist of a doubling, or two-fold layer of the inner membrane; and with this statement no fact of which we are aware is at variance. A hard prominent line, which generally marks the attachment of their fixed margin to the vein, is asserted by Bichat to consist of the proper venous tissue, the fibres of which, he says, alter their direction for this purpose; and when the common or inner membrane reaches this line, it doubles or folds itself to form the valve, which thus consists of two layers of the inner or common membrane. This, however, is denied by Hunter, who considers them of a tendinous nature, and by Gordon, who made several unsuccessful attempts to split these two layers.
Valves are not uniformly present in all veins. They are found, 1st, in the following branches of the superior great vein—the internal jugular, the azygos, the facial veins, those of the arms, &c.; 2d, in the following branches of the inferior great vein—the divisions of the posterior iliac, of the femoral, tibial, internal and external saphenous, and in the spermatic veins of the male.
They are wanting in the trunk of the inferior great vein (vena inferior), in the renal, mesenteric, and other abdominal veins, in the portal vein, in the cerebral sinuses, in the veins of the brain and spinal chord, in the veins of the heart, of the womb generally, and of the ovaries, and perhaps in all other veins less than a line in diameter. In the cerebral sinuses the transverse chords are supposed to supply their place.
In the lungs they were supposed to be wanting, till their presence was established by Mayer of Bonn.
In situation the valves vary considerably. In general they are found in those parts of venous canals at which a small vein opens into a larger. But even from this arrangement there are deviations. The only valve which is definite and invariable in its situation is the Eustachian (valvula Eustachiana, valvula nobilis), which is always placed at the cardiac end or beginning of the inferior vena, where that vessel is attached to the sinus of the right auricle. Shaped in general like a crescent, the attached margin of which is the arch of a large circle, and the free that of a small one, it proceeds from the left extremity of the sinus downwards, forwards, and towards the left side, where it is insensibly lost on the membrane of the auricular septum. At its lower end it generally covers the orifice of the large coronary vein. This membranous production is always larger, more perfect, and more distinct in the fetus and in the infant, than in the adult. In the latter it is almost always reticulated; and sometimes the only vestige of its existence is a thin chord or two representing its anterior margin. I have seen it reticulated even at the age of sixteen or seventeen, and almost destroyed beyond thirty. Haller was much perplexed to account for the use of this membranous fold. The conjecture of Bichat, that it is connected with some purpose in the fetal circulation, is entitled to regard.
Dr Gordon mentions a third partial substance, which is occasionally found in local patches at various parts of veins. This I believe to be the deposit found at the union of two veins to form one trunk.
Besides the cellular or filamentous envelope, veins receive capillary arteries, to which there are corresponding veins. The arteries rise from the nearest small ramifying arteries; and the corresponding veins do not terminate in the cavity of the vein to which they belong, but pass off from its body, and join some others from different parts; and at last terminate in the common trunk somewhere higher. Nervous branches, or rather filaments, are observed in the pulmonary artery and great veins only. Are they derived from the great sympathetic, as is generally said?
In the veins, as in the arteries, the anatomist recognises two extremities, the cardiac or collected, and the organic or the ramified. Examined physiologically, however, the terms origin and termination are not of the same import as when applied to the arteries. In reference to the veins, they become convertible terms; and it is the General usage even of writers on anatomy to represent the veins as arising where the arteries terminate, and terminating at the organ from which the latter arise. This distinction must be kept in view in the following observations.
The cardiac extremity or termination of the veins is so well known as to render any minute explanation unnecessary.
The organic extremity or origin of the venous system is more obscure and difficult to be understood. It is indeed impossible to trace the origin of the small venous vessels, unless in the manner in which Leeuwenhoek, William Cowper, Henry Baker, Haller, and Spallanzani did in their observations on the transparent parts of animals in general cold-blooded. From the experiments of these observers, we know that a very small vessel, evidently tending and conveying blood towards a larger, connected with a venous branch, may be seen passing directly from a similar small vessel, as evidently conveying blood from a larger, which is connected with the arterial system. All that we know from this, however, is, that a vein containing red blood may rise from an artery conveying red blood. This is matter of observation; all beyond is little more than conjectural.
Haller, indeed, admits origins of veins as manifold as the terminations of the arterial system, a view in which he has been followed by almost all subsequent authors; and Bichat states it as a leading proposition, that the veins arise from the general capillary system. Neither conclusion is founded on strict observation; and while that of the former physiologist is derived chiefly from uncertain facts and loose analogies, the statement of the latter is too hypothetical and general to be either entirely true or wholly false.
Of one fact only are we certain. The blood which is conveyed into the small vessels and the substance of the tissues and organs is brought back by the veins. We have seen that the only origin which is strictly susceptible of demonstration is that of the red vein from the red artery. The point then to be ascertained is, whether colourless veins and absorbent veins arise from the several textures, as colourless and exhalant arteries terminate in them. The proper place for the further examination of this question is the subsequent section.
I must not omit to mention, nevertheless, that the veins have been shown to be connected at their ramified extremities with the lymphatics.
When the veins become distinct vessels, branches, and trunks, they become once more objects of sensible examination. In their course from their organic to their cardiac extremities they present various circumstances which merit attention.
1. In general every artery is accompanied by a venous tube, which is divided in the same manner, and furnishes or receives an equal number of branches. Thus the descending aorta is accompanied by the vena cava inferior; the common iliac arteries by common iliac veins; the anterior iliac, femoral, and popliteal, by anterior iliac, femoral and popliteal veins. These veins are deep-seated, and are generally named the concomitant veins (venae comites et venae satellitae). In some situations an artery may be accompanied either in its trunk or in its branches by two veins of equal size. Thus in general the brachial artery, and its branches the radial and ulnar, are each accompanied by two veins. The only situations in which the number of veins can be said to be exactly equal to that of the arteries, are in the stomach, in the intestinal canal, in the spleen, in the kidneys, in the testicles, and in the ovaries.
2. In the extremities and in the external regions of the trunk we find, in addition to the concomitant veins, an external layer of venous tubes immediately beneath the skin, (venae subter cutem dispersae, Pliny). These subcutaneous or superficial veins do not correspond to any artery; but as they are chiefly destined to convey the blood from the skin and other superficial parts, they open into the deep-seated veins. Thus in the case of the basilic and cephalic, two superficial veins of the arm, the former, after passing the bicipital fascia, forms in the sheath the brachial vein; and becoming the axillary in the axilla, receives the latter vessel. In the same manner the saphena (φασιν επιφυλη, vena manifesta), or superficial vein of the leg, passes through the falciform process of the fascia lata to join the femoral vein.
From this it results that the venous canals are on the whole more numerous than the arterial. In a few situations only a single vein corresponds to two arteries, as in the penis, the clitoris, the gall-bladder, and the umbilical chord. Often also in the renal capsules and the kidneys two or more arteries have only one corresponding vein. In such circumstances the vein is always large and capacious.
It has been generally stated that the calibre and area of the venous tubes are much larger than those of the corresponding arteries, and consequently that the capacity of the venous system is much greater than that of the arterial. I acknowledge that I know not on what exact evidence the former of these propositions, the only one with which the anatomist is concerned, is made to rest. If it be mere inspection in the dead subject, or the effects of injection, little doubt can be entertained that the alleged greater calibre depends chiefly on the laxity and distensible nature of the venous fibre. The arterial tubes appear small in consequence of annular contraction, or the tendency which they have to collapse, when the distending force has ceased to operate. The venous canals appear large by reason of their distension and distensibility during life, from the tendency to accumulation in their branches in most kinds of death, except that by hemorrhage, and from a smaller degree of the physical property of shrinking and annular contraction when empty.
When a vascular sheath is exposed in the human subject, as in the operation for aneurism, or in the lower animals in the way of experiment, the vein generally appears larger than the corresponding artery. This, however, is never so considerable as it is represented by most authors, and certainly cannot afford grounds for the estimates which Kessel, Jurin, and other mathematical physiologists have assigned to the relative capacity of the arteries and veins. It is also to be observed that something of this greater size depends on the increase of dilatation resulting from removing the pressure of incumbent parts. In young animals also the difference between the size of the veins and their corresponding arteries is so trifling as to be scarcely discernible. This shows that
---
1 Arcana Naturae Detecta: Opera Omnia, tom. ii. p. 160, 168. 2 Philosophical Transactions, No. 239, p. 1179. Cowper saw this communication of arteries and veins not only in cold-blooded animals, as the lizard, tadpole, and fishes, but in the omentum of a young cat and a dog. 3 On Microscopes, and the discoveries made thereby. London, 1755, 2 vols. 8vo. 4 Experiments on the Circulation of the Blood, by Lazzaro Spallanzani; translated by W. Hall. London, 1891. something is to be ascribed to the incessant operation of a dilating force increasing uniformly with the duration of life.
Upon the whole, it is chiefly on the ground of their larger numerical arrangement that the veins collectively can be said to be more capacious than the arteries. On this subject some observations of Bichat are entitled to attention.
3. The veins in general accompany the arteries. The venous trunk placed contiguous to the arterial in the same sheath, is divided into branches at the same points, and is distributed into the substance of organs much in the same manner. From this arrangement, however, certain deviations are observed in particular regions. Thus, in the brain, neither the internal carotid, nor the basilar artery, nor their large branches, are accompanied with veins. The small branches only have corresponding veins, which, as they unite to form large ones, pour their blood into the venous canals termed sinuses, the arrangement of which is unlike any other part of the venous system. In the chest also a different disposition of the venous from the arterial tubes is observed. The cavae cavae, though conveying the blood to the pulmonic division of the heart, as the aorta conveys it from it, do not, however, correspond with the latter either in situation or in dependent branches. The azygos and the hemiazygos veins, in like manner, which receive the intercostal veins, have no concomitant artery, but open into the superior cava, to which they may be viewed as appendages. Lastly, The portal vein, which is formed of the united trunks of the splenic, superior mesenteric and inferior mesenteric veins, corresponds to no individual arterial trunk, and forms of itself a peculiar arrangement in the venous system.
Some anatomists have dwelt much on the more superficial and less sheltered situation of the veins than of the arteries. On this point no positive inferences can be established. In the extremities the former are in general most superficial; but in the interior of the body, especially in the chest, the venous trunks are quite as deep-seated as the arterial.
The course of the venous canals is in general more rectilineal and less tortuous than that of the arteries. In no part of the venous system is such an inflection presented as that which the internal carotid makes in the carotic canal. The general result of this is, that a set of venous tubes is shorter than a corresponding set of arterial ones. The trunks also are less infected than the branches.
4. The mutual communications of the venous system (anastomoses, inosculationes,) are more numerous and frequent than those of the arterial. 1. The minute veins communicate so freely as to form a perfect net-work. 2. In the twigs, though more rare, these communications are still frequent. 3. In the branches, though less numerous, they are nevertheless observed; and in this respect alone the venous must be greatly more numerous than the arterial inosculations, which are confined chiefly to the smaller and more remote parts of the system. These inosculationes, indeed, between the venous branches constitute one of the most peculiar and important characters of their arrangement, in so far as by their means the communication is maintained between the superficial and deep-seated vessels of the system. Thus the emissary veins are the channel of communication between the cerebral sinuses and the temporal, occipital, and other external veins. The external and internal jugulars communicate by one or two considerable vessels; and the free communication between the basilic and cephalic by the median veins, that between them and the deep brachial vessel, and that between the saphena and its branches and the femoral vein, are sufficiently well known. The application of these anatomical facts to the ready motion of the venous blood is obvious.
But of all the communications between the branches or large vessels of the venous system, the most important, both anatomically and physiologically, is that maintained by means of the vena azygos between the superior and inferior cavae. The azygos itself is connected at its upper or bronchial extremity with the superior cava, and at its lower extremity it is in some subjects connected directly with the inferior cava, in others by means of the right renal vein, and in most by the first lumbar veins. By means of the hemiazygos, again, it is connected with the left renal vein, or the lumbar of the same side, and in some instances directly with the inferior cava. To the azygos and hemiazygos, therefore, belongs the remarkable property of connecting not only the venous canals of the upper and lower divisions, but those of the right and left halves of the body.
System of Capillary Vessels.—Terminations of Arteries,—Origins of Veins.
Though we can scarcely, with propriety, speak of the capillary tissue, or the tissue of capillary vessels, we find it requisite to introduce in this place the general facts of the anatomical peculiarities of this important part of the human body.
The term capillary system, though much spoken of in physiological and pathological writings, is perhaps not always precisely defined or distinctly understood. According to Bichat, it is not only the common intermediate system between the arteries and veins, but the origin of all the exhalant and excreting vessels. If we consider the modes in which arteries have been said to terminate, and veins to take their origin, we find, that in this view of the capillary system there are some things which are doubtful, and some which are inconsistent with the rest.
Haller, and most of the physiological authorities since his time, concluded, chiefly from the phenomena of injections, sometimes from microscopical observation, and, where these failed, from the obscure and uncertain evidence of analogy, that an artery traced to its last or minute divisions will be found to terminate in one or other of the following modes. 1st, Either directly in a red vein or veins; 2d, in excreting ducts, as in the lacrymal and salivary glands, the kidney, liver, and pancreas, the female breast, and the testicle of the male; 3d, in exhalingants, as in the skin, in the membranes of cavities (serous membranes); the cavities of the brain, the chambers of the eye, the filamentous tissue, the adipose cells, the pulmonary vesicles, and mucous surfaces and their follicular glands; 4th, in smaller vessels, for instance lymphatics; and, 5th, in the colourless artery (arteria non rubra).
A similar application of the same facts has assigned to the veins a mode of origin not unlike. If, therefore, we admit the definition given by Bichat, it follows that the capillary system consists, 1st, of minute arteries communicating with veins; 2d, of excreting ducts; 3d, of exhalingants; and, 4th, of minute arteries or veins containing a colourless portion of the blood. It is obvious, however, that it is absurd to say that the system of capillary vessels at once comprehends and gives origin to the excretories and exhalingants. In other respects the whole of
---
1 Anatomie Générale, tome i. p. 378. 2 Ibid. vol. i. p. 471. Système Capillaire, article 1. 3 Elements Physiologique, lib. i. sect. 1, p. 22-29. One of the first distinct and intelligible descriptions of the physical characters and arrangement of the capillary vessels was given in 1831 by Dr. Marshall Hall, from microscopical observations made on the vessels of the fin and tail of the stickleback, the web of the frog's foot, the mesentery of the toad, and the lungs of the salamander, frog, and toad.
The arteries, veins, and intervening capillary vessels as seen in the lung of the toad, highly magnified.
In the web of the foot of the frog, the minute arteries are characterized by their straight course and small size, by the light colour and rapid motion of their contents, and by a distinct pulsatory movement, which extends not to the capillaries. The arteries are nearly equal in number to the veins.
Capillaries in the web of the foot of the frog (A. Thomson).
The latter, which first strike the eye, are tortuous, red, and present the most distinct view of the blood moving within their canals in single globules or successive rows. Though Dr. Hall could in no instance detect any anastomosis or in-
---
1 Gordon, p. 58. 2 Ibid., p. 26. osculation between the minute arteries, except in the mesentery of the toad, this arrangement was frequent among the veins, and in the anastomosing branches of two apparent veins a double and contrary current of blood is sometimes observed. In no instance could Dr Hall observe a distinct termination of an artery or a vein, and the medium of communication between these two orders of tubes is generally, if not invariably, Capillary Vessels.
The manner in which arteries pass into capillary vessels is the following.—The large arteries first divide into branches. These subdivide into smaller branches, which by successive subdivision terminate in tubes, which are successively smaller than those from which they issue. At a certain point of this subdivision, a small artery is observed to terminate in two, each of which is equally large as itself; and these vessels further traced are observed not to terminate in smaller tubes, but to communicate with others of the same size as themselves. At this point the course of the blood becomes of only half its former velocity; and the globules, instead of moving too rapidly to be seen, become distinctly visible. To this order of vessels, which open into, and communicate exclusively with others of the same calibre, and in which the blood is observed moving so much more slowly than they did in the decreasing vessels, that the motion of individual globules may be observed, the author restricts the denomination of Capillary System. The object of the uniform diameter, and its concomitant phenomenon, retarded motion, he thinks is obvious, since by this arrangement the blood is retained in the vessels of organs, a sufficient time for the accomplishment of the functions of nutrition and secretion. The capillaries, therefore, are situate intermediate between the arteries and veins, and their character is that they form minute cylinders, and have a uniform diameter, while the arteries and veins are conical.
Alcohol applied to these vessels has the effect of interrupting the motion of blood within them; and by applying this fluid to the web of the frog's foot, two layers of capillaries are brought into view; one superficial, in which the motion of the blood is suspended, the other deep-seated, in which it is still moving.
Of the pulmonary capillaries, the arrangement is slightly modified. The division of the minute arteries into capillaries is more immediate, and without those successive subdivisions observed in the arteries of the systemic circulation. On the other hand, the capillaries open into the veins with equal abruptness, and without the gradual reunion observed in the minute veins of the systemic order. These ultimate arteries also give off capillaries, not only from their extremities but from their sides, by minute pores; and the veins receive capillaries in the same manner. The arteries and veins in no case communicate by direct anastomosis, at least in the lung of the salamander. The intermediate vessels, on the contrary, which constitute the capillaries, insinuate in every possible manner, and infinitely more frequently than in the systemic order, and hence constitute an extensive network of cylindrical tubes, of uniform diameter. Through this network the blood flows with extreme rapidity in a uniform current; and as each artery communicates with several capillaries, the blood appears to run like diverging rays from a point or line, and to converge in the same manner, when it proceeds from the capillaries opening into the pulmonary veins. It may be inferred, that one effect of this arrangement is to distribute the moving globules over a surface as extensive as possible, and thus to expose the greatest possible number of them, in a given time, to the inspired air.
This is the distribution of the Capillary Vessels in the lung of the salamander. In the frog and toad, the lungs of which combine the vesicular and cellular arrangement, it is much the same, with this exception, however, that the arteries, previous to their termination in capillaries, follow the external margins of the vertical meshes of which the vesicles consist, while the veins run along their internal margins.
This account applies of course to the capillaries of the Saurial and Batrachoid Reptiles. But there is every reason to believe, that the same arrangement takes place in the Mammiferous class of animals.
The difference of the capillary network depends on three circumstances: 1. The calibre of the tubes; 2. the diameter of the interposed spaces between these tubes; and 3. on the shape of these spaces.
1. The calibre of the tubes varies in different tissues and organs. The smallest are still large enough to allow the blood corpuscules to pass one after the other; consequently, in man, the smallest capillaries are not much below 0.003 of one line. This rate is also given by the measurements of Weber from preparations injected and dried in the method of Lieberkühn. In some parts they vary between 0.004 and 0.005 of one line; and Valentin estimates the smallest vessels of the stomach at 0.0057 in diameter, and in the ileum at 0.0048. Müller represents those of the kidney to range between 0.0037 and 0.0069 of one line.
2. The dimensions of the intervening spaces depend in some measure on the fulness of the tubes. The fuller these are, the smaller are the interstitial spaces. The spaces in the vascular network of the white substance of the brain are, according to C. H. Weber, 0.0142 broad, and 0.025 long; in length, consequently, from eight to ten times, and in breadth from four to six times larger than the diameter of the capillary vessels. In the capillary network of the mucous membranes and the external skin, the meshes are often only between three and four times larger than the diameter of the vessels—often of the same width, or even narrower. In the kidneys, Müller found the diameter of the capillary vessels, in relation to the intervacular spaces, as 1 to between 3 and 4.
3. As to figure, Henle distinguishes two principal shapes; the roundish and the oblong. But besides these, some assume the square figure, others the polygonal, and some are irregular.
escribes two great capillary systems in the human body: 1st, The general one, or that which consists of the minute terminations of the aortic divisions, and the origins of the superior and inferior great veins; and, 2nd, the pulmonary capillary system, or that which consists of the minute terminations of the pulmonary artery, and the origins of the pulmonary veins. The general capillary system further consists of an individual capillary system, not only for every organ, but in some instances for every tissue. The brain possesses an individual capillary system; and that of the membranes is evidently distinct from that belonging to the organ itself. The heart and the kidneys possess each an individual capillary system; and the liver may be said to have two, one formed by the communication of the hepatic artery and veins, and another consisting of the divisions of the portal vein, with the branches of the hepatic hollow vein; (Vena cara hepatica).
The organic properties of the capillary vessels are as little known as their structure. Many physiological and pathological writers, especially experimentalists, have ascribed to them a power which has at different times been called muscular, tonic, irritable, contractile; and have asserted that, because the larger arteries are provided with a fibrous membrane, which they have called muscular, and to which they have ascribed irritability, or the power of contraction when stimulated, their minute or
---
1 A Critical and Experimental Essay on the Circulation of the Blood, p. 29. General capillary terminations must have the same property. This conclusion is completely unfounded for two reasons. 1st, I have already shown that the proper arterial tunic is not muscular in structure, and, according to the best experiments, possesses no property of contraction when stimulated. 2d, Although it be admitted that the proper arterial tissue is muscular and irritable, it is quite certain that observation has not hitherto shown that this tunic can be recognised in arteries smaller than a line in diameter; and in the capillaries properly so called, that is, in vessels which partake of the nature of artery and vein, no such structure has yet been observed.
It is not improbable, however, that the capillaries possess certain organic or vital properties; but all that has been taught on this subject is either hypothetical or derived from an insufficient and imperfect collection of facts. It is certain that the blood which moves through them is beyond the direct influence of the action of the heart, and can be affected by this only so far as it keeps the larger vessels constantly distended with a column of blood which cannot retrograde, and must therefore move forward in the only direction left to it. It has been, therefore, argued that the capillaries must have an inherent power of contraction, by which this motion is favoured. Is it not sufficient to say that they act merely as resisting canals, to prevent their contents from escaping, and to minister to the various tissues and organs those supplies of blood which the several processes of nutrition, secretion, &c., require?
The effects which the application of mechanical irritants, or chemical substances, as alcohol, acids, and alkalies, produced in the experiments of Hunter, Wilson Philip, Thomson, and Hastings, have been supposed to demonstrate the irritable nature of the capillary vessels. The conclusion is illegitimate, in so far as the results of these experiments are open to several sources of fallacy. In some instances these effects are to be ascribed to incipient inflammation, in others to shivering of the capillary structure, or crisping by chemical action, in others to actual coagulation of the blood of the capillaries; but none of them prove satisfactorily any peculiar properties in the vessels of which the capillary system is composed.
While the views of Reuss, and the experiments of Dutrochet, Wedemeyer, and Kaltenbrunner, render it probable that the capillaries possess some contractile power, they by no means prove that this is adequate to impel the blood through them, independently of the impulse of the heart. According to the hypothesis of Reuss, the arterial system is in a state of positive, and the venous in that of negative, electricity; and by the operation of this agent the blood is made to move from the former class of vessels through the capillaries into the latter. From the experiments of Dutrochet, again, on the transmission of fluids through organic membranes, that author infers that, by means of the inward and outward impulse, or that property which he denominates Endosmose and Exosmose, the blood flows through the capillaries into the veins. Lastly, Wedemeyer, who further maintains that the impulsive force of the heart is propagated to the capillary system, concludes, from the effects of injecting fluids, both mild and irritative, and from microscopic observation, combined with the effects of mechanical and chemical irritants, that the capillaries possess considerable contractile power, the operation of which is under the influence of galvanism, or General nervous energy, or both; but that this, instead of promoting, ought to resist the motion of the blood through them.
Erectile Tissue. (Vasa Erigentia,—Vascula Erectilia,—Tissu Erectile.)
The system of capillary arteries and veins does not present the same arrangement in all situations and in all the tissues of the human body. A peculiar arrangement of these vessels was early recognised by our countryman William Cowper, who states that he demonstrated the direct communication of arterial and venous canals, not only in the lungs, but in the spleen and penis, "in which," says he, "I have found these communications more open than in other parts." This fact, however, was long overlooked by subsequent anatomists.
Among the terminations of arteries enumerated by Haller, one which he referred to the head of exhalants was that of a red artery or arteries pouring their blood into the spongy or cellular structure of the cavernous bodies of the nipple, the clitoris, and the penis, that of the wattles of the turkey, and the comb of the cock. His detailed examination of those parts shows, that, with a correct knowledge of their anatomical structure, he had not a very distinct conception of the manner in which their vessels are disposed. It was afterwards observed, however, by John Hunter, that the spongy structure of the urethra and glans consists of a plexus of veins.
Bichat remarked that the spleen, and the cavernous body of the penis, instead of presenting, as the serous surfaces, a vascular or capillary net-work, in which the blood oscillates in different directions according to the impulse which it receives, exhibit only spongy or lamellar tissues, still little known in their structure, in which the blood appears often to stagnate instead of moving. As this peculiar structure was known in the cavernous body to be the seat of a motion long known by the name of erection, MM. Dupaytren and Richerand distinguished this arrangement of arteries and veins as a peculiar tissue, under the name of erectile,—a distinction which, though partly understood before, has only now been admitted as well founded in the writings of anatomical authors. According to the recent arrangements of M. Bechard this tissue comprehends not only the structure of the cavernous body, but that of the spongy substance (corpus spongiosum), which incloses the urethra, and forms its two extremities, the bulb and gland, the clitoris, the nymphæ, and the nipple of the female, the structure of the spleen in both sexes, and even that of the lips.
It is unfortunate that the researches of anatomists on this erectile tissue have been restricted chiefly to the spongy body of the urethra and the cavernous body of the penis; and it is rather by analogy than direct proof that similarity of structure between them and the other parts referred to the same head is maintained. I shall here state what is ascertained.
The cavernous body of the urethra, or what is now termed its spongy body, is represented by Haller to consist of fibres and plates issuing from the inner surface of the containing membrane, and mutually interlacing, so as to form a series of communicating cells, into which the
---
1 Philosophical Transactions, No. 285, p. 1396. 2 Additions à l'Anatomie Générale de Xav. Bichat, par P. A. Bechard, p. 118. 3 Haller applies the name of cavernous body not only to the structure of the penis, but to that of the urethra. (Elementa Physiologica, lib. xxvii. sect. 1.) 4 Elementa Physiologica, lib. ii. sect. 1, § 24. 5 Ibid. lib. xxvii. sect. 1, § 33. General proper urethral arteries pour their blood directly during the state of erection.
The cavernous body of the penis is in like manner represented to be a part of a spongy nature, or to consist of innumerable sacs or cells separated by plates and fibres, which at the moment of erection are distended with blood poured from the arteries, and which is afterwards removed by some absorbing power of the veins.
This opinion, which was that of many subsequent anatomists, even Bichat himself, was derived apparently from the facility with which the blood so deposited escapes, not, as it was believed, from divided vessels, but from areolar, or interlaminar spaces. It appears, however, to have been at variance with what had been anciently taught by Vesalius, Ingrassias, and Malpighi, and positively stated regarding these vessels by Hunter; and modern researches have shown it to be completely erroneous. Cuvier and Ribe in France, Mascagni, Paul Farnese, Moreschi in Italy, and Tiedemann in Germany, have shown that there are no cells or spongeform structure in the erectile tissue of the cavernous body.
The first correct view of the structure of parts of this description in the human subject was given by Mascagni in his account of the arterial and venous communications in the spongy body of the urethra. In 1787 he announced in his work on the Lymphatics, that the parts called cavernous bodies, both in the penis and in the clitoris, are simply fasciculi, or accumulations of arterial and venous vessels without interruption of canal; but that between the arteries and veins of the spongy bodies a dilated cavity or minute cell is interposed. In 1795 repeated minute injections led him to doubt the existence of this sort of cell; and about the close of 1805 he publicly demonstrated the fact, that many veins of considerable calibre, collected in the manner of a plexus, with corresponding arteries, but small and less numerous, really form the outer and inner membranes of the urethra, the whole of the glans penis, and the whole substance of the spongy body. In each of these parts, and also in the spongy structure inclosing the orifice of the vagina, he ascertained by repeated injections that there are no cells, as was imagined, and that the arteries, reflected as it were, give origin to numerous veins, which, forming an intimate plexiform net-work, constitute the whole glans, and the entire vascular body which surrounds the urethra and the entrance of the vagina.
In the cavernous bodies of the penis and clitoris he had not sufficient facts to ascertain the existence of the same structure, as he had never succeeded in injecting these parts so completely as the glans and the spongy part of the urethra. Eventually, however, he succeeded, especially in children, in injecting fully these cavernous bodies of the penis and clitoris. He found in their interior nothing but fasciculi of veins, with corresponding arteries, but rather smaller. He inferred, therefore, that these vessels, collected and ramified in various directions, constitute a vascular texture capable of expanding and shrinking, according to the quantity of blood conveyed to it.
The general accuracy of this description has been since confirmed by the researches of Paul Farnese and Moreschi. The latter, especially, has shown, 1st, that the glans consists of arteries and a very great number of minute veins, which pour their blood into the cutaneous dorsal vein; 2d, that the urethra, and especially its posterior part, may in like manner be shown to consist of numerous minute veins, which terminate in a posterior branch of the dorsal vein, and communicate with the veins of the bulbous portion of the urethra; and, 3d, that in the cavernous bodies, though also receiving blood-vessels, these are much less numerous, and are chiefly derived from the urethral vessels.
The same arrangement was recognised by Cuvier in the penis of the elephant, by Tiedemann in that of the horse, by Shaw in the human subject and in the horse, and by Mr Houston in the tongue of the chameleon.
Upon the whole, the facts collected by different anatomists on this subject furnish the following results.
If the arteries, on the one hand, be injected, they are found to terminate in very fine ramifications, the disposition of which is exactly the same as in other parts. If, on the other, the veins be injected, it is easy to perceive the two following circumstances: 1st, That they are much dilated at their origin, that is, that the venous radicula are really more dilated than might be anticipated from the other characters of these vessels; 2d, That the tubular dilatations to which they are accessory form very numerous inoculations or anastomoses, precisely as the capillary system of which they constitute a part. The effect of this arrangement is to give these vessels the appearance of being penetrated with sieve-like openings, resembling areolar, or interlaminar spaces mutually communicating. As the whole difference, therefore, between the capillary vessels of this and other parts of the human frame consists in the minute veins (radicula venosa) being dilated or distended in a peculiar manner, Belclard concludes that the erectile tissue of the cavernous body consists simply of minute arteries and dilatable veins interwoven in the manner of capillary nets. These distended venous cavities are indeed so remote from being cells, that they are truly continuous with veins, the inner membrane of which may be easily recognised among them.
During erection the blood accumulates in this tissue; but the cause and mechanism of this accumulation are completely unknown.
Since these observations were made, Johann Müller of Berlin has, by injecting the arteries of the penis, been enabled to give an account of the characters of Erectile vessels, something more detailed and specific.
By injecting the principal artery of the penis before its subdivision, and dividing longitudinally one of the corpora cavernosa, the ramifications of the nutrient arteries are seen upon the inner side of the venous spaces, the arteries becoming gradually smaller, until they pass into the capillary net-work, where their divisions cannot be seen by the naked eye. Besides these nutrient ramified arteries there is seen, on careful inspection, another set of arterial branches, of
---
1 "Sed et in pene, et in clitoriide, et in papilla mammae, et in collo galli indici, nimis manifestum est, verum sanguinem effundit, neque unquam ejus color totus de illis partibus evanescit, quae ab effuso sanguine turgere solent." (Elementa, lib. xxvii, sect. 3, § 10.)
2 Systema Anatomiae, sect. 3, p. 596.
3 Le arterie vi si ritorcono, e danno origine alle vene, e queste formano in seguito alcuni plessi, i quali accumulati in varia maniera, costituiscono tutto il glande, e tutta quella massa vascolare, che trovasi intorno al canale dell' uretra, e all' ingresso della vagina." (Prodruck della Grande Anatomia di Paolo Mascagni, capitolo ii. p. 61. Firenze, 1819, folio.)
4 Prodruck del Pene Manuale, loco citato, p. 61.
5 Considerationes de Urethra Corporis Glansque Structura &c idus Decembris 1610 detecta, Alexandri Moreschii, Eq. Coron. Ferrari, in Ticinensi primum, tum Bononiensi Archigymnasio Anatomiae Professoris. Mediolani, 1617.
6 Medico-Chirurg. Trans. vol. x. p. 338, 333. London, 1619.
7 Trans. of Royal Irish Academy, 1828.
8 Additions, p. 119. General Anatomy.
ize, shape, and disposition, which are given off nearly at right angles, from both the large and small trunks. These arterial processes are about one-hundredth part of one inch in diameter, and one-twelfth long; and are clearly seen by the naked eye. They project into the cavities of the spongy substance, and terminate either in blunt extremities or in dilated extremities, without undergoing any division or ramification. These short arterial processes are turned round at their extremities into a semicircle or more, and present a spiral appearance like the end of a cork-screw. This disposition suggested to M. Müller the name of Helicine, or Spiral or Screw-like Arteries (Arteriae Helicine).
The helicine arteries of the penis are more easily seen in man than in any other animal examined by Professor Müller. He found them in all the animals in which he sought for them; they are to be seen at the posterior part only of the penis in the stallion, but in the dog exist throughout the whole organ.
In man the helicine twigs of the penial arteries sometimes come off singly; at other times they form tufts or clusters, consisting of from three to ten branches, and having in general one very short common stem. The swelling at the extremity, when present, is gradual, and is greatest a little way from the end. The helicine branchlets given off from large arteries are not of greater size than those coming from small ones; and even the smallest capillary arteries of the Profunda Penis, which can be seen with the aid of a glass alone, give off helicine twigs of a much greater size than themselves.
Each helicine branchlet projecting into a venous cavity is covered by a thin membrane, which Professor Müller regards as the inner coat of the dilated vein; and when there is a tuft of helicine twigs, the whole tuft is covered with one envelope of a gauze-like membrane. This covering is considerably thicker on the helicine arteries in the posterior part of the Corpus Spongiosum Urethrae, than in the Corpus Cavernosum; but it is possible that this is in some measure connected with the state of repletion of the arteries; for when the injection has gone well, it becomes difficult to distinguish the external covering.
Professor Müller could not discover any apertures either on the sides or on the ends of the helicine arteries. But he seems to regard it as probable that there are minute apertures, which may be of that nature that they allow the passage of the blood in certain states and not in others.
The helicine arteries are not, as some may suppose, loops of vessels which have been incompletely filled, and which, after forming a coil, pass into venous spaces, as E. H. Weber found to be the case with the arteries of the maternal portion of the placenta. Müller, it is seen, distinguishes in the branches from the Arteria Profunda, p. 800, two orders of vessels; one Rami Nutritii, corresponding to the arteries of other organs which serve the purpose of nutrition, and pass continuously into the veins; the others, Rami Helicinei, with shut ends, forming processes or shoots from the Arteria Profunda, bent in the manner of tendrils which project into the cells or spaces of the Corpora Cavernosa, and, according to the conjecture of Müller, pour the blood during erection through openings in their ends immediately into the spaces of the Corpora Cavernosa. Their diameter is between 0.07 and 0.08 of one line.
The helicine arteries are more numerous towards the root than near the point of the penis. They are observed in the Corpus Spongiosum Urethrae, especially towards its bulb; but are not there so easily seen as in the Corpora Cavernosa. They have not hitherto been observed in the Glans.
Their structure is nearly the same in all the animals in which they have been examined. The helicine arteries of the ape bear the nearest resemblance to those of man; and in most animals they are less obvious than in the human subject. In the horse and dog, they give off from their sides small nutrient twigs, which render them more difficult to be seen in these animals than in man.
---
1. Ueber die Arterie Helicine, von Johann Müller. Archiv fur Anatomie und Physiologie, Heft II., 1835. 2. Müller's Archiv fur Anatomie und Physiologie, 1838. Seite 182. 3. Müller's Archiv, 1837. Seite 31. 4. Oesterreichen Jahrbuch, 1838, xix. 349. 5. Allgemeine Anatomie. Seite 486. Leipzig, 1841. General accompanied with obvious enlargement of this organ, which subsides at the conclusion of the paroxysm. It appears that the same phenomenon takes place during digestion.
Sir Everard Home, with the assistance of the microscopic inspection of M. Bauer, has made many observations on the structure of this organ. But his purpose appears to have been more particularly directed to ascertain the phenomena of its function and uses; and I cannot discover that his ideas on its intimate structure, and the arrangement of its capillary system, are precise or distinct.
The most distinct examples, therefore, of erectile tissue are to be found in the spongy texture which surrounds the urethra, in the cavernous body of the penis, in the vessels of the clitoris, the vascular structure of the nymphae, and in the nipple of the female. The structure of the lips in both sexes is not unlike. The veins of these parts may be shown to be well marked and largely dilated at their origin, so as to give the appearance of cellular net-work. The same disposition is observed in the pulp of the fingers. It has been attempted to explain the motions of the iris by supposing it to be formed of this erectile tissue; but the justice of this conjecture seems doubtful.
In the tissue now described it is manifest that the physiologist ought to place the phenomena of the process distinguished by the name of vital turgescence (turgor vitalis) by Hebenstreit, Reil, Ackermann, and Schlosser. Though these authors suppose vital turgescence in different degrees in almost all the textures of the animal body, their most distinct examples are taken from those parts which consist of erectile vessels. After the explanation of the anatomical structure above given, it is superfluous to seek for any other cause except the arrangement of the minute vessels, and especially that of the veins.
System of Exhalants. Exhalant System. (Vasa Exhalantia.—Système Exhalant.)
Exhalants. Are there such vessels as the exhalants described by physiological authors? Is their existence proved by observation or inspection? If not, what are the proofs from which their existence has been inferred?
The existence of minute arteries, the open extremities of which are believed to pour out various fluids in different tissues of the human body, has long been a favourite speculation with physiological anatomists. The decreasing vessels (vasorum continuo decrecscentium multum subique succedentes ordinis), and exhalant orifices of Boerhaave, must be known to almost all. Haller ascribes to the skin, membranes of cavities (serous membranes), ventricles of the brain, the chambers of the eye, the cells of the adipose membrane, the vesicles of the lung, the cavity of the stomach and intestines, an abundant supply of these exhalant arteries or canals, which, according to him, pour out a thin, aqueous, jelly-like fluid, which, in disease, or after death, is converted into a watery fluid susceptible of coagulation. The existence of these vessels, he conceives, is established by the watery exudation which appears in these several parts after a good injection of the arteries.
hese minute canals, however, through which this injected fluid is believed to percolate, have never been seen, or rendered capable of actual inspection, their existence was denied by Mascagni, who ascribed the phenomena of exhalation to the presence of inorganic pores in the arterial parietes, through which, he imagined, the fluids transuded to the membranes or organs in which they were found. This mechanism, which was equally invisible with the Hallerian, was, for obvious reasons, denied by Bichat, who resolved to reject every opinion not founded on anatomical observation, and to determine the existence of the exhalants by this evidence alone. Obliged, however, to avow the difficulty of forming a distinct idea of a system of vessels, the extreme tenacity of which prevents them from being seen, he undertook to attain his object by what he terms a rigorous train of reasoning.
This consists in the effects observed to result from successful injections of watery fluids, or of spirit of turpentine containing some finely levigated colouring matter; from the phenomena of active hemorrhage, which Bichat considers merely as exhalation of blood instead of serous fluid; and from numerous considerations unfolded in the further prosecution of the subject. In this manner he concludes, that the only points ascertained are, 1st, the existence of exhalants; 2d, their origin in the capillary system of the part in which they are distributed; and, 3d, their termination on the surfaces of serous and mucous membranes, and the outer surface of the corion or true skin.
The exhalant vessels, the existence, origin, and termination of which he thus proved, he distinguished into three classes. The first contains those exhalants which are concerned in the production of the fluids which are immediately removed from the body,—the cutaneous and the mucous exhalants; the second contains those exhalants which are employed in the formation of fluids which, continuing a given time on various membranous surfaces, are believed to be finally taken again into the circulation by means of absorption; and the third class consists of the exhalants concerned in the process of depositing nutritious matter in the different tissues and organs of the human frame. This arrangement is more distinctly seen in the following table.
| Exhalants | 1. Exterior, opening on natural surfaces or cataneous canals | Mucous | |-----------|----------------------------------------------------------|--------| | | 2. Interior, opening on membranes, or within cellular textures | Serous, Synovial, Cellular, Medullary | | | 3. Nutritious |
Each organic tissue is in this system supposed to have its appropriate exhalant arteries, from which it derives the material requisite for its nutrition.
The clearness and regularity of this arrangement would render it desirable that the existence of these vessels were demonstrated with certainty. It is evident, however, that the regularity of arrangement is the only advantage which it possesses over the views of those authors whose method and opinions Bichat professed not to follow. The existence of exhalants is as little proved
---
1 Brevis Expositio Doctrinae Physiologicae de Turgore Vitali, 1795. 2 Opuscula, vol. ii. opusc. vi. 3 Archie, für die Physiologie, i. band, 2. heft, s. 172. 4 Ackermann, Physiologische Darstellung der Lebenskraft, 1797, i. band, s. 11. 5 Georgii Eduardi Schüssler Dissertatio de Turgore Vitali, Extat in Brera Syllage, vol. vii. opusc. ii. 6 Haller, Elementa, lib. ii. sect. 1, and his notes on Boerhaave, Protectiones, tom. ii. p. 243. 7 "Aqueum humorem de arteria perinde exhalarce, olei teretinthine allorumve pigmentorum, et vivi argenti iter persuadet, quod anatomica manu impulsum, aut omissio vivo in homine a consuetis naturae viribus eo deductum, in ejus humoris, quam vocant, came-rum depletur." (Elementa, lib. vii. sect. 2, § 1.) General in the rigorous reasoning of Bichat as in the fanciful theories of Boerhaave, the generalizing conclusions of Haller, or the bold supposition of lateral porosities by Mascagni. This defect in his system has therefore been recognised both by Magendie and Beclard, the first of whom, though he admits the existence of exhalation as a process of the living body, allows that no explanation of its mechanism or material cause has been given, and asserts that Bichat has created the system of vessels termed exhalants; while the second thinks that anatomical observation furnishes no evidence of their existence.
The colourless capillaries, he observes, which are admitted by all, and the existence of which is satisfactorily established by the well-known experiment of Bleucland, proves nothing whatever concerning the existence of exhalant vessels; for these colourless arteries are observed to terminate in colourless veins, and there is no proof hitherto adduced of their proceeding further, or terminating by open mouths. He admits that the fact of exhalations in the living body, of nutrition, of transudation by arterial extremities, shows that these extremities possess openings through which the fluids of exhalation, the materials of nutrition, and the matter of injection, escape. But whether these openings are found at the point at which the capillary arteries are continuous with veins, or belong to a distinct order of vessels continued beyond these arteries, is a question which observation has not yet determined, and which it perhaps is unable to determine. Such is the present state of knowledge in relation to the existence of exhalant arteries. While the process of exhalation is admitted, we must avow, as Cruikshank did long ago, that we are unable to prove satisfactorily the existence of any set of vessels, or any mechanism by which it might be accomplished.
**Lymphatic System. (Vasa Lymphatica, Vasa Lymphifera, Lymphae-Ductus of Glisson and Jolyffe,—Systeme Absorbant.—Die Saugadern.)**
In most situations of the human body, and especially in the vicinity of arterial and venous trunks, there are found long, slender, hollow tubes, pellucid or reddish, which present numerous knots, joints, or swellings in their course, and to which the name of lymphatics or absorbents has been given. It is most expedient to employ the former appellation only, as the latter implies the performance of a function, the reality of which has been much questioned of late years.
Though Eustachius had seen the thoracic duct in the horse, and some slight traces of a knowledge of vascular tubes, different either from arteries or veins, are found in the writings of Nicolaus Massa, Fallopius, and Veslingius, the merit of establishing their existence is generally ascribed to Caspar Aselli, a physician of Pavia. This anatomist, who had in 1632 seen the white-coloured tubes, then first named lacteals, issuing from the intestines of the dog, observed also a cluster of vessels less opaque near the portal eminences of the liver,—an observation which he afterwards repeated in the horse and other quadrupeds. The same vessels were also described and delineated by Highmore.
Passing over the uncertain and obscure hints given by Walrus and Van Horne, the first exact information after General Aselli is that which relates to Olaus Rudbeck, who, in Anatomy, 1650, is said to have seen them in a calf, and to have demonstrated the thoracic duct, and the dilated sac, afterwards termed receptaculum chyli.
Glisson informs us that Jolyffe had in 1652 imparted to him the knowledge of a set of vessels different from arteries and veins; and it appears, from the testimony of Wharton, that Jolyffe had demonstrated these vessels in 1650. In short, the discovery of lymphatics, and the correction of some errors of Aselli, are ascribed to the English anatomist, not only by Wharton and Glisson, but by Charleton, Plott, Wotton, and Boyle.
The existence of these vessels, thus partially demonstrated, was afterwards more fully established by the researches of Bartholin, Pecquet, Bilsius, Nuck, the second Monro, and Haller. It is chiefly to the exertions of William Hunter, and his pupils Hewson, Sheldon, and Cruikshank, in this country, and to those of Mascagni in Italy, that the anatomical world are indebted for the complete examination and history of this system of vessels.
The lymphatic vessels consist, in the members, of two layers, a superficial and a deep-seated one. The first is situated in the subcutaneous cellular tissue, between the skin and the aponeurotic sheaths, and accompanies the subcutaneous veins, or creeps in the intervals between them. A successful injection of these superficial lymphatics will show an extensive net-work of mercurial tubes surrounding the whole limb.
The deep-seated layer of lymphatics is found chiefly in the intervals between the muscles, and along the course of the arterial and venous trunks. In tracing both layers of lymphatics to the upper, fixed, or attached end of the members, we find they increase in volume and diminish in number. At the connection of the members with the trunk, they are observed to pass through certain spheroidal or spherical bodies, termed lymphatic glands or ganglions. The lymphatics of the upper extremity, after passing through the glands of the armpit, terminate in trunks, which open into the subclavio-jugular veins, one on each side of the neck. Those of the lower extremity, after passing through the glands of the groin, proceed with the common iliac vein into the abdomen, where they unite with other lymphatics.
The lymphatics of the trunk consist in like manner of two layers, a subcutaneous and deeper seated one, distributed in the chest between the muscles and pleura, and in the abdomen between the muscles and peritoneum. In the chest and belly, each organ possesses a superficial layer of lymphatics distributed over its surface, and pertaining to its membranous envelope; the other ramifying through its surface, and pertaining to the peculiar tissue of the organ. This twofold arrangement is most easily seen in the lungs, the heart, the liver, spleen, and kidneys.
In a similar manner are arranged the lymphatics in the external parts of the skull; on the face, where they are very numerous; in the spaces between the muscles; and on the neck, in which they pass through numerous glands. No lymphatics, however, have been found in the brain, the spinal chord, their membranous envelopes, the eye, or the ear.
---
1 Francisci Glissonii Anatomia Hepatis, cap. xxxi.; Thomas Wharton Adenographia, cap. ii. p. 93. 2 Experimental Inquiries, Part the second; by William Hewson, F.R.S. London, 1774, 8vo. 3 The History of the Absorbing System, &c. by John Sheldon, surgeon, F.R.S. &c. London, 1784, folio. 4 The Anatomy of the Absorbing Vessels of the Human Body, by William Cruikshank. London, 1786, 4to. 5 Pauli Mascagni Variorum Lymphaticorum Corporis Humani Historia et Iconographia. Paris, 1767, folio. See also Prodromi, &c. All the lymphatics hitherto known terminate in two principal trunks. One of these, termed from its site thoracic duct (ductus thoracicus, die Milchbrustrohre, le canal thoracique), is situated on the left side of the dorsal vertebrae. It receives the lymphatics of the lower extremities, of the belly, and the parts contained in it; those of great part of the chest, and those of the left side of the head, neck, and trunk, and left upper extremity. The other lymphatic trunk, which is situated on the right side of the upper dorsal vertebrae, is formed by the union of the lymphatics of the right side of the head, neck, right upper extremity, and some of those of the chest. Both of these trunks open into the subclavio-jugular vein of each side.
That lymphatics terminate in branches of the venous system, has been asserted on the authority of various observers. Steno, for instance, states that he traced the lymphatics from the right side of the head, the chest, and pectoral extremity, in animals, into the right axillary vein; and he gives delineations of anastomotic connections of several lymphatics with the axillary and jugular veins. Similar facts have been reported by Nuck, Richard Hale, Bartholin, and Hartmann. Ruysh traced the lymphatics of the lung into the subclavian and axillary veins; Drelincourt those of the thymus gland in animals into the subclavians; and Hebenstreit saw those of the loins pass into the vena azigos.
Haller, though unwilling to deny the testimony of these observers, considers it liable to various sources of fallacy, and doubts the direct communication of the lymphatic and venous systems. By John F. Meckel the grandfather, nevertheless, this communication was maintained, from the circumstance that he found mercury injected into the lymphatics pass into the veins without any traces of extravasation. From injecting the lymphatics also he found the inferior cava full of mercury, not a particle of which had passed by the thoracic duct into the superior cava. Injecting afterwards an indurated lumbar gland from a pelvic lymphatic, when he found its lower half only was filled, he increased the pressure, with the view of filling the minute vessels of the gland. When this was continued a little, he observed the fluid metal pass into the inferior cava, and thus traced the minute lymphatics into the venous system.
These facts have received too little attention, from the circumstance that Hewson, though not doubting them as stated by the author, regarded them as liable to considerable fallacy, and, along with William Hunter, imputed the effect in question entirely to extravasation. Both Hunter and Hewson, indeed, appear to have injected veins from lymphatics in the same manner in which Meckel did; but both saw reason to infer that extravasation had taken place. Cruikshank, again, states that he never saw a lymphatic vessel inserted into any other red veins than the subclavians and jugulars. The termination remarked by Steno and his successors constitutes in truth the common trunk or lymphatic vein admitted by Cruikshank—a thoracic duct of the right side.
Recently this mode of termination has been revived by Tiedemann and Fohman, who state that, in the seal, the lactiferous vessels communicate with veins arising from the mesenteric glands, and pass thence into the venous trunks without proceeding through the thoracic duct. General M. Lauth junior, of Strasburg, again, conceives that he has demonstrated that lymphatics communicate with veins within the substance of organs, and in the interior of the lymphatic glands—an inference which at present requires further verification. The statements of Lippi of Florence, that every lymphatic almost communicates freely with venous tubes, is still more improbable, and has been rendered exceedingly doubtful by the recent researches of Rossi.
The connections of the ends of lymphatics with the organs and tissues from which they arise, termed their origins, are completely unknown. In some favourable instances the lymphatics of the intestinal canal are so filled with a reddish or whitish fluid after the process of digestion has continued for some time, that not only are their larger branches easily seen, but by the aid of the microscope some of the smaller may be traced to their commencement. This, which was ascertained by Cruikshank (p. 55 and 58), and confirmed by Hewson, Bleuland, and Hedwig, has been contradicted by the observations of Rudolph and Albert Meckel. In all other parts, however, though a successful injection may show the course and distribution of many of the smallest lymphatics, yet no orifices are perceptible at the point at which they seem to stop, and we are uncertain whether these points are their origins. (Cruikshank.) Mere observation is here as unavailing as in regard to the termination of exhalants. The continuation of lymphatics with arteries, unless in the case of those which arise from the interior of arterial tubes (Lauth), is not satisfactorily established. It has been conjectured, however, that their ends or imperceptible origins are connected to the tissues to which they are traced, and that the lymphatics arise in this manner from these tissues.
The lymphatics are distinguished by being in general cylindrical in figure, and by varying in calibre at short spaces. In this respect they differ from the arteries and veins. It has been further justly remarked by Gordon, that the middle-sized lymphatics are remarkably distinguished from the corresponding parts of the arterial and venous system by three peculiarities: 1st, When two lymphatics unite to form a third, the trunk thus formed is seldom or never larger than either of them separately; 2dly, their anastomoses with each other are continual; and, 3dly, they seldom go a great space without first dividing into branches, and then reuniting into trunks.
The outer surface of a lymphatic is filamentous and rough, the inner smooth and polished, like that of small veins. It is impossible to observe the structure of these tubes in the middle-sized, or even in the large lymphatics; and anatomists have generally been satisfied with supposing that the structure of all of them is similar to that of the thoracic duct, or some other large vessels equally susceptible of examination. According to the observations of Cruikshank (chap. xii.), which have been verified by Bichat, the thoracic duct presents, 1st, a layer of dense, firm, filamentous or cellular tissue, exactly similar to that found inclosing arterial and venous tubes, which the latter regards as foreign to the vessel, but giving it a great degree of support and protection; 2dly, a proper membrane, delicate, transparent, and moistened inside by an unctuous fluid, which he seems inclined to
---
1 Nova Experimenta et Observationes de fluidis Venarum ac Vasorum Lymphaticorum, sect. 1, p. 4. Lugub. Bat. 1772. 2 Anatomische Untersuchungen über die Verbindung der Sangaderen mit den Venen. Heidelberg, 1821. 3 Essai sur les Vaisseaux Lymphatiques. Strasbourg, 1824. 4 Illustrazioni Fisiologiche e Patologiche del Sistema Linfatico-Chilifero mediante la scoperta di un gran numero di comunicazioni di caso col vescovo del Professore Regolo Lippi. Firenze, 1825. 5 Cenni sulla comunicazione dei vasi linfatici colle vene. di Giovanni Rossi, Doctor, &c. Annali Universali di Medicina, anno 1826, vol. xxxvii. p. 52. General anatomy. Muscular fibres, of which Sheldon speaks positively, Cruikshank represents, though seen in some instances (chap. xii.), yet to be more generally not demonstrable. Their existence, though admitted by Schreger and Soemmering, is denied by Mascagni, Rudolph, and J. F. Meckel, and, I may add, by Bichat and Beclard. This account differs not much from that of Dr Gordon, who could not recognize distinctly more than one coat, similar to the inner coat of veins. The filamentous layer noticed by Bichat, and considered by Mascagni as an external coat, is of course excluded.
The knotted or jointed appearance of lymphatics is occasioned chiefly by short membranous folds in their cavity, called valves. These folds are thinner than the venous valves; but they are equally strong, and have the same shape and mode of attachment to the inside of the vessel. They are generally found in pairs, but never three at the same point. A single valve is sometimes found at the junction of a large branch with a trunk, or of a trunk with a vein. According to Cruikshank, there is considerable variety in the distribution of valves; but in general a pair of valves will be found at every one-twentieth of an inch in lymphatics of middling size. In the larger lymphatics they are less numerous than in the small. The structure of these valvular folds is as little known as that of the inner membrane, of which they appear to be prolongations. According to Mascagni, they sometimes contain a small portion of fine adipose substance.
The tissue which forms the lymphatic tubes is strong, dense, and resisting; and from the weight of mercury which they bear without rupture, it has been generally concluded that they are stronger in proportion to their size than veins. This tissue also possesses considerable elasticity.
The opposite states of lymphatics during digestion and after long fasting, and the phenomena of mercurial injections, prove that the tissue of which they consist is distensible and contractile. Though it does not exhibit appearances of muscular structure, it has been long supposed to be endowed with a property analogous to irritability. Such is the inference which Hunter, Hewson, Cruikshank, and others, have derived from various phenomena in the living and recently dead tissue.
Though Bichat doubts what he terms organic sensible contractility, yet he admits insensible contractility as necessary to the functions ascribed to lymphatics. Previous to his time Schreger, in different experiments, observed the first of these qualities, in consequence of the application not only of acids, butter of antimony, and alcohol, but even of hot water and cold air. Similar contractions and relaxations have been induced by mechanical irritation. Such phenomena are observed not only during life, but even after death; and if to this we add, that the thoracic duct is often after death large and flaccid, though empty, but in the living body is almost always contracted and scarcely visible, and that a portion of it included between two ligatures, and punctured, quickly expels its contents, it may be inferred that the lymphatic tissue possesses a considerable degree of this organic property.
Lymphatic Gland or Ganglion, Kernel. (Glandula Lymphatica;—Glandula Conglobata;—Die Saugader-Drüsen.)
This is the proper place to consider the structure of those bodies which are in common language termed kernels, to which anatomists have applied the name of lymphatic glands, and the French anatomists have more recently given that of lymphatic ganglions. The usual appearance, figure, and situation of these bodies are well known. General in general they are spheroidal, seldom quite globular, and most commonly their shape is that of a flattened spheroid. In different subjects, and in subjects at different ages, they vary from two or three lines to an inch in diameter. The medium rate is about half an inch. Their surface is smooth; their colour grayish-pink, sometimes pale red, bluish, or of a peach-blossom tinge,—varieties which seem to depend on degrees of bloody transudation; for, when washed and slightly macerated, they assume the gray or whitish-blue colour. In a few instances they are jet black,—a peculiarity which seems to depend on a degree of black infiltration, or on the incipient stage of that change which has been termed melanosis, or melanotic deposition. The idea that it may be derived from the carbonaceous matter suspended in the atmosphere of great cities, has been shown by Cruikshank to be absurd. Its anatomical possibility may be justly questioned.
They are always situate in the cellulo-adipose tissue found in the flexures of the joints. They are found in small number at the bend of the arm, and that of the elbow; in the armpit and groin they are more numerous; in considerable number in the cellular tissue of the lumbar region, before the psoas and iliacus muscles; and they are most abundant round the neck. The posterior mediastinum, and the cellular tissue between the mesentery and vertebral column, abound with lymphatic glands mutually connected in clusters.
Each gland may be said to consist of a peculiar substance, inclosed in a thin membrane like a capsule. The capsule is a thin, pellucid, colourless substance, which is resolved by maceration into fine whitish fibres. It is very vascular; and Mascagni appears to have detected absorbents in it. It is connected to the proper substance by fine filamentous or cellular tissue. The capsule is considered by Beclard as a fibro-cellular membrane. The proper substance of lymphatic glands consists of a homogeneous pulp, in which injections have shown numerous ramifications of minute vessels. As these vessels are injected from the lymphatics which are seen to enter the body of the gland, they are believed to be continuous with them, and to be lymphatics arranged in a peculiar manner. These vessels are of two kinds, one entering the gland, called vasa afferentia or inferentia, entrant lymphatics; the other quitting, are called vasa efferentia, egressient lymphatics. This distinction is founded on the direction of the valves. In the vasa inferentia the free margins of the valves are turned towards the gland; in the vasa efferentia they are turned from it.
The number of entrant lymphatics varies from one to thirty, and, what is more remarkable, very rarely corresponds with that of the egressient lymphatics, which are in general much fewer. Cruikshank states that he has injected fourteen entrant lymphatics to one gland, to which only one egressient vessel corresponded. When the entrant lymphatic reaches the gland, it splits into many radiated branches, which immediately sink into its substance. The egressient lymphatics are generally larger than the entrants.
The arrangement of these vessels in the interior of the glands is best described by Mascagni, whose observations are confirmed by Gordon. To see this well, it is requisite to inject the entrant lymphatics of two glands in two different modes; one with mercury, the other with wax, glue, or gypsum. After a successful mercurial injection, the entrants are seen, before sinking in the gland, to divide into two orders of branches. One of them, which belongs chiefly to the surface or circumference of the gland, consists of large vessels, bent, convoluted, and in- General terwoven in every direction, communicating with each other, and swelling out into dilated cells at certain parts; and of smaller vessels, which form a minute net-work on the surface, and which seem to terminate in the cells or distended parts of the larger vessels.
From these distended parts or cells, again, arise many minute vessels, which, after winding about on the surface of the gland, unite gradually, and form the egressient vessels of the gland.
The wax, glue, or gypsum injection is employed to show the deep-seated or central vessels of the gland. The distribution of these is found to be quite the same as that of the superficial vessels.
The cells delineated by Cruikshank I am disposed to regard as more dilated parts of the lymphatic vessels which constitute the intimate structure of the gland.
These minute tubes are connected by delicate filamentous tissue, which is more abundant in early life than afterwards.
Injections show the existence of blood-vessels which accompany the convolutions of the lymphatics in the glands; but no nerves have been found either in the glands or their capsules.
The white matter described by Haller and Bichat is not contained in the cellular substance, but in the cells of the lymphatic vessels themselves.
The three orders of tubes or canals, the anatomical characters of which have now been completed, constitute what has been termed the Vascular System; (Vasa; Systema Vasorum; Das Gefass System; Le Système Vasculaire.) The great extent of its distribution, and the part which it performs in all the processes of the living body, both in health and during disease, must be easily understood. In every texture and organ arteries and veins are found; and in all, except a few, the art of the anatomist has demonstrated those colourless valvular tubes denominated lymphatics. The arrangement of the former, especially in the substance of the several textures, essentially constitutes what is termed the organization of these textures. Many anatomists have imagined that each texture has a proper matter, or parenchyma, by which it was supposed to be particularly distinguished, and which was conceived to consist of minute, inorganic, solid atoms. Whether this opinion be well founded or not, it is perhaps of little moment to inquire. At present it is certain that it is not susceptible of demonstration.
The phenomena of injections, in which he was eminently successful, led Ruysch to entertain the opinion, that every substance of the animal frame consists of nothing but vessels. This idea, though opposed by Albinius, on the same grounds on which it was advanced, was nevertheless revived by William Hunter, who believed that the inorganic parts of animal bodies are too minute for sensible, or even microscopical examination. In every part, however minute, always excepting nails, hair, tooth enamel, &c., vessels may be traced; and even a cicatrix, he demonstrated, is vascular to its centre.
By the aid of the microscope the researches of Lieberkühn tended still more powerfully to favour this opinion. But repeated observation of the effects of injection in every part and texture almost of the body, by Barth and Prochaska, has led the latter to conclude that this opinion, understood in the ordinary mode, is not tenable. Prochaska, who has investigated this subject with much attention, thinks he is justified in dividing all the substances of the animal frame into two,—those which may be injected, and those which cannot. In this manner he regards skin, especially its outer surface, muscle, various parts of the mucous membranes, the pia mater, the lungs, the muscular part of the heart, the spleen, the liver, kidneys, and other glands, as very injectible; but tendon, ligament, cartilage, &c., as not injectible. Without entering minutely into the merits of this distinction, or the inferences which Prochaska deduces from it, it is sufficient, so far as all useful knowledge is concerned, to infer that blood-vessels are an essential constituent of every organic texture, however different; and if there be any other matter inherent in such textures, it must be derived from these as a secretion. Nerve, brain, muscle, osseous matter, and cartilage, are depositions or the product of nutritious secretion from the respective arteries of these organized substances.
Nerve, Nervous Tissue. (Nervus.—Nervus.—Tissu Nerveux.—Système Nerveux.)
The nervous system of the animal body includes two general divisions. The first of these, named Brain and spinal Chord, is collected in a single and indivisible mass, and contained in a peculiar cavity, formed by part of the osseous system of the animal,—the vertebral column, and cranium, in the Vertebrated animals generally. The second division of the nervous system, with which alone we are at present concerned, is found in the form of long chords or threads mutually connected, and running in various directions through the body in the mode of ramification. To these the name of nervous trunks or chords, or simply nerves, has been long applied.
The structure of the nerves has been examined with different degrees of accuracy and minuteness by a great number of anatomists. The more ancient authors, who wrote at a period when observation was much corrupted by fancy, and most of those who gave descriptions in general systems, may be without much injustice passed over in silence. It is sufficient to say that some good facts are given in the works of Willis, Vieussens, Morgagni, and Mayer; that Prochaska, Pfeffinger, the second Monro, and Fontana, are the first who professedly wrote on the structure of the nerves; that the works of Reil, Bichat, and Gordon, contain the most accurate information on the nervous chords in general; and that the treatises of Scarpa and Wutzer contain the best descriptions of the arrangement of those parts named ganglions and plexuses.
Lastly, by the microscopic researches of Ehrenberg, Treviranus, Berres, Müller, Purkinje, Valentin, Weber, Burdach, Remak, and Pappenheim, some facts, though rather discordant, have been communicated on the minute structure of the microscopic filaments.
All the nervous chords of the animal body may be distinguished in physical characters into two different orders, which, though frequently mingled with each other, neverthe-
---
1 Annotationum Academiarum lib. iii. 2 Medical Observations and Inquiries, vol. ii. 3 De Villis Intestinis. 4 Georgii Prochaskae Disquisitiones Anatomicae-Physiologicae Organisatis Corporis Humani ejusque Processus Vitalis. Vienna, 1812, 4to. 5 J. C. Reil, Exercitatio Anatomica de Structura Nervorum. Halle, 1797. 6 Anatomiae accuratae Annotationum liber primus de Nervorum Gangliis et Plexibus. Auctore Antonio Scarpa. Ticini, 1792. 7 De Corporis Humani Gangliorum Fabrica alia Utn Monographia. Auctore Carolo Gulielmo Wutzer, Med. Chirurg. Doc. &c. Berolini, 1817. General less possess sufficiently different properties to enable the observer to distinguish them, independent of knowledge of their intimate structure.
Nerves. The first order of nerves are firm, glistening white, marked by cross-stripes, and are distributed principally to the muscles of the trunk and the skin. The second order are soft, reddish-gray in colour, flat, much interwoven with each other, and belong more to the viscera, and accompany the blood-vessels. The former have knotty swellings only at their origins, and at spots where they form connections with nerves of the second sort; the latter are in all parts occupied by small knots. The white nerves of the first order are named animal, or Cerebro-spinal nerves; the gray nerves of the second are known as soft, entropic, sympathetic, vegetative, or organic, also as vascular or Ganglial nerves.
The following description applies to the nerves of the first order, unless where the contrary is expressly stated.
Each nerve forms connections in three different ways. 1st, A nerve must be connected to some part of the central mass by one of its extremities,—the cerebral or spinal end; 2d, it must be connected to some texture or organ, or part of an organ, by the other extremity,—the organic end; and, 3d, it may be connected to other nerves by a species of junction called anastomosis (ansa), anastomosing or uniting point. By means of the first two connections, it is supposed to maintain a communication between the central mass and the several organs; and by the latter it is understood to be subservient to a more general and extensive intercourse, which is believed to be necessary in various functions and actions of the animal system.
Every nerve consists essentially of two parts; one exterior, protecting, and containing; the other interior, contained, and dynamic, forming the indispensable part of the nervous structure.
The first of these, which has been known since the time at least of Reil by the name neurilema (νευρονεύρων, νευρονεύρων), or nerve-coat (Nervenhaute, Reil; Nervenhülle, Meckel), has the form and nature of a dense membrane, not quite transparent, which is found on the outside of the nervous chord or filament, and invests the proper nervous substance. It must not, however, be imagined that the neurilema forms a cylindrical tube, in the interior of which the nervous matter is contained. The latter disposition, if it actually exists, applies to the smaller nerves only, and to some of those which go to the organs of sensation,—a peculiarity which we shall notice subsequently.
Any large nervous trunk, for example the spiral or median of the arm, or the sciatic nerve of the thigh, is found to be composed of several small nervous chords placed in juxtaposition, and each of which, consisting of appropriate neurilema and nervous substance, is connected to the other by delicate filamentous tissue. These, however, do not through their entire course maintain the parallel disposition in respect to each other, but are observed to cross and penetrate each other, so as to form an intimate intercalation of nervous chords and filaments, each of which, however minute, is accompanied with its investing neurilema. The neurilema, in short, may be represented as a cylindrical membranous tube, giving from its inner surface many productions forming smaller tubes (canaliculi; die Nervenröhre; primitive cylinders of Fontana), in which the proper nervous matter is contained.
Of this arrangement the consequence is, that each nerve or nervous trunk, enveloped in its general neurilema, is composed nevertheless, of a number, more or less considerable, of smaller chord-like nervous threads (funiculi nervosi, Prochaska; chordes, funes, Nervenstränge, Reil), into which the nerve, by maceration and suitable preparation, may be resolved. Each chord, again, or nerve-string, as Reil terms it, though invested with a proper neurilem, may be further resolved into an infinite number of minute filiform or capillary filaments (fila, fibrilla, Nervenfasern, Reil), which, invested in a delicate covering, are understood to constitute the ultimate texture of the nerve.
This threefold division may be easily observed in the brachial and spiral nerves of the arm, and still more distinctly in the sciatic in the thigh. The utility of understanding the internal arrangement from which it results will appear forthwith, when the structure of those parts termed ganglions and plexuses comes under examination.
Of this arrangement in different nerves, and in different regions, this membrane undergoes great modification; and all opinions on its nature derived from thickness or transparency are liable to considerably fallacy. Scarpa seems to view it as connected, in anatomical origin and character, with the hard membrane (membrana dura, dura mater). Reil, who devoted more care and time to the examination of its nature and structure than any other inquirer, represents it as consisting of cellular substance, many bloodvessels, and some lymphatics. Bichat thinks it resembles the soft membrane of the brain (pia meningis, pia mater), and is derived from it. The neurilema of the cerebral nerves may be regarded as consisting of soft membrane (pia mater) at their origin, but in all other situations as a species of filamento-fibrous membrane.
The connection supposed by Mayer to exist between the neurilema and the pia mater was disproved by Reil; and though its analogy with the denticulated ligament were established, it would prove nothing regarding the neurilema. Upon the whole, the idea of Reil is the most probable. According to the observations of this anatomist, who examined the neurilema after fine and successful injection, it is liberally supplied with bloodvessels. These proceeding from the neighbouring arteries penetrate the filamentous sheath of the nerve; and, immediately on reaching the neurilema, diverging at right angles, generally run along the nervous threads (funes), parallel to them, forming numerous anastomotic communications, and divide into innumerable minute vessels, which penetrate between them into the minute neurilematic canals. So manifold is the ramification, and so minute the distribution, that in these canals not a particle of nervous substance is found which is not supplied with a vessel. The arrangement of the veins is analogous.
It appears, therefore, that the neurilema is a tissue of membranous form, with a multiplied mechanical surface, liberally supplied with bloodvessels, from which the nervous matter is secreted and nourished. It is impossible, indeed, to doubt that, of the two parts which compose the nervous chord, it is the most perfectly organized; and that, though it may not be similar in structure to the pia mater, it is quite analogous in the use to which it is subservient. Like that membrane, it sustains the vessels of the nerve; it presents a multiplied surface, over which the vessels are distributed; and, by penetrating deep into the body of the nerve, it conveys the nutritious vessels in the most capillary form to the inmost recesses of the nervous substance.
The arrangement which has been above described is the
---
1. The term dynamic is used to denote in a general sense the properties of animal substances. 2. Observations sur la Structure des Nerfs, &c., apud Traité sur le Vein, &c., par M. Felix Fontana. Florence, 1781. 3. Reil, Exercitationes Anatomicae de Structura Nervorum, cap. i. p. 3. 4. Anatomie Générale, p. 137, &c. 5. De Structura Nervorum, cap. v. p. 19. 6. Reil, Exercitationes Anatomicae de Structura Nervorum, cap. i. only one which can be regarded as general. It varies in particular regions; and these varieties in the neurilematic disposition occur principally in the nerves which are distributed to the proper organs of sensation. 1st, The olfactory nerve is soft, pulpy, and destitute of neurilema, from its origin in the Sylvian fissure, to the gray bulbous enlargement which terminates its passage in the cranium; but as soon as it reaches the conical or grooves of the ethmoid bone, and begins to be distributed through the nasal anfractuosities, it is distinctly neurilematic. 2d, The optic nerve is still more peculiar in this respect. The instant it quits the optic commissure (commissura tractuum), it begins to be invested by a firm general neurilema, which sends into the interior substance of the nerve various membranous septa or partitions, forming separate canals, in which the nervous matter is contained. These partitions, however, are so thin, that at first sight the optic nerve seems to consist merely of one exterior membranous cylinder inclosing the proper membranous substance. 3d, Lastly, we may remark, that the auditory nerve, or the soft portion of the seventh pair of most anatomical writers, is the only nerve in which this covering cannot be traced.
The neurilema is much thinner and more delicate in the nerves which are distributed to the internal organs, as the lungs, heart, stomach, &c., (nerves of the organic life, great sympathetic and pneumogastric nerves par vagum,) than in those belonging to the muscular system.
The second component part of the nervous chord or filament is the proper nervous matter which occupies the cavity of the neurilematic canals. Little is known concerning the nature or organization of this substance. It is whitish, somewhat soft, and pulpy; but whether it consists of aggregated globules, as was attempted to be established by Della Torre and Sir Everard Home, or of linear tracts disposed in a situation parallel to each other, as appears to be the result of the inquiries of Monro, Reil, and others, or of capillary cylinders containing a transparent gelatinous fluid, as Fontana represents, seems quite uncertain. It has been presumed, rather than demonstrated, that it resembles cerebral substance. But this analogy, though admitted, would throw little light on the subject; for at present it is almost impossible to find two anatomical observers who have the same views of the intimate nature of cerebral substance itself. Whatever be its intimate arrangement, it appears to be a secretion from the neurilematic vessels. (Reil.)
The structure of the nervous chord may be demonstrated in the following manner. When a portion of nerve is placed in an alkaline solution, the whole, or nearly the whole, of the nervous matter is softened and dissolved, or may be washed out of the neurilematic canals, which are not affected by this agent, and the disposition of which may be then examined and demonstrated. Aquous maceration may likewise be advantageously employed to unfold this structure; for it separates and decomposes the cellular tissue by which the neurilematic canals are united, and subsequently occasions decomposition of the nervous substance, while it leaves, at least for some time, the neurilema not much affected. When, however, the maceration is too long continued, it is separated and detached like other macerated textures.
Lastly, If a large nerve be placed in diluted acid for the space of one or two weeks, the neurilema is gradually dissolved, and the nervous matter becomes so much indurated and consolidated, that it may be separated from the contiguous chords in filaments with great facility. In undergoing this change, the portion of nerve becomes much shorter and considerably contracted,—is subjected, in short, to the process of crispation; so that unless a large nerve like the sciatic be employed for the experiment, it may be impossible to obtain the result in the most satisfactory form. These experiments, with many others of the same nature, were first performed by Professor Reil, and afterwards repeated and varied by Bichat and Gordon.
The minute structure of the nerves has been examined by Fontana, Prochaska, Bauer, Ehrenberg, Valentin, Muller, Wagner, Remak, and Purkinje. But the results at which they have arrived are far from agreeing with each other; and either from the difficulty of the subject, and the minuteness of the objects, or from imperfections in the observations, it is next to impossible to present an account consistent and intelligible.
M. Bauer found the optic nerve to consist of many bundles of very delicate fibres, connected together by means of a jelly-like, transparent, semi-fluid, viscid substance, easily soluble in water. These fibres consist of rows of globules, which are from \( \frac{1}{800} \)th to \( \frac{1}{600} \)th part of one inch in diameter, with a few at \( \frac{1}{400} \)th part of one inch in diameter; the latter being the size of the red globules of the blood, when deprived of colouring matter. The Retina appeared like a continuation of the bundles composing the optic Nerve, consisting of the same sized globules connected into fibrous lines, and forming bundles radiating from the end of the nerve to the circumference of the Retina, where they disappear, terminating in smooth membrane.
Before noticing the observations of Ehrenberg, it may be proper to state that he distinguishes the following forms of organic structure, as visible by the microscope in the Brain or its parts, the Spinal Chord, and Nerves.
1. A series of tubes which present, at definite intervals, globular or spheroidal expansions, so as to resemble a string of beads which do not touch each other, but have a short communicating space interposed between each bead. To these tubes Ehrenberg gives the name of Varicose, from their resemblance to the Varices of a vein, and Jointed or Articulated tubes, because of the slight resemblance to a set of joints. The best name for them is Moniform, or beadlike, when they really resemble a string of beads. These tubes, which present to the microscope the appearance of parallel fibres, he shows by various proofs to have an internal cavity, and to contain a peculiar matter, to which he assigns the name and qualities of nervous fluid. They are confined chiefly to the white matter of the brain; but occur also in several of the sensiferous nerves.
2. A set of tubes, straight and uniform, without the alternate spheroidal enlargements, also hollow, and to which he applies the name of Simple Cylindrical Tubes. These are found chiefly in the nervous trunks and chords. These are generally larger and coarser than the Articulated Tubes; but in certain points the latter are found to pass into the former by gradually losing their bead-like enlargements. These tubes he further represents to be distinguished from the Cerebral Jointed Tubes, by containing in their interior a viscid, white, but less transparent matter, to which he applies the name of Medullary.
3. Besides the two now mentioned, Ehrenberg mentions
---
1 By the term "proper organs of sensation" are understood those of sight, hearing, smell, and taste, which are confined to a fixed spot in the system. 2 Reil, de Structura Nervorum, cap. I. p. 3 and 5. 3 According to the experiments of Reil, nitrous acid diluted with water answers best. Muriatic acid, though equal or even superior in effecting solution of the neurilema, softens the nervous matter too much, and separates the component filaments too completely. (De Structura Nervorum, cap. iii. p. 16.) 4 Philosophical Transactions, 1821 and 1824. General Anatomy.
A substance consisting partly of very minute fine grains, with some coarser-grained matter disseminated, as is said in the language of mineralogy, through the fine-grained matter. The latter is confined entirely to the gray matter of the convoluted surface of the Brain, and the laminated surface of the Cerebellum.
The olfactory, optic, and auditory nerves, Ehrenberg found to consist of varicose or moniliform medullary tubules, directly continued from the moniliform tubes of the white cerebral matter. The moniliform tubules of the olfactory nerves are the thickest known, and vary from $\frac{1}{4}$th to $\frac{3}{8}$th part of one line in diameter. Those of the optic nerve are smaller, being from $\frac{1}{2}$th to $\frac{1}{8}$th part of one line in diameter; and tubules of the same dimensions are observed in the Chiasma or Decussation, in which the tubules are represented as crossing each other; while the Retina consists of articulated tubules $\frac{1}{8}$th part of one inch in diameter, traversing medullary grams about $\frac{1}{8}$th part of one line in diameter. It contains also mace-like or club-shaped bodies, that is, bodies terminating in thick round ends.
The structure of the Auditory Nerve is peculiar. The simple tubules of this nerve Ehrenberg found considerably thicker than those of the others, and the spheroidal enlargements or ampullae flatter, and less permanent, yet everywhere distinctly seen. In other respects it was similar to the olfactory and optic nerves.
The great Sympathetic Nerve, in like manner, consists of articulated cerebral tubules; but there is at each extremity a mixture of simple cylindrical tubules.
The nerves now specified, the Olfactory, Optic, Auditory, and Great Sympathetic, are Articulated or Moniliform Nerves.
All the other nerves consist not of Articulated or Moniliform tubules, but of simple cylindrical tubules somewhat larger, being from $\frac{1}{8}$th to $\frac{1}{4}$th part of one line in diameter. These tubules are surrounded and enclosed by vascular networks, and contained within ligamentous or neurilematic partitions; and they contain a medullary substance, semifluid, but capable of expression from them, and of coagulation within their interior. These are Tubulated Nerves.
The ganglia vary in structure. All consist of articulated or bead-like cerebral tubules, which, either alone, as in the Chiasma, form the knot, or, as in all the ganglia of the sympathetic examined, are mingled with large cylindrical nervous tubules, enclosed within a close slender vascular network, between the meshes of which are deposited granules similar to those observed in the Retina.
The tubules and cylinders now specified, which correspond with the primitive cylinders of Fontana, are merely in juxtaposition, and do not intermingle in substance with each other.
Neither Ehrenberg nor Müller were able to recognise in the roots of the sensiterous and motorious nerves any essential difference in microscopic structure.
In the hypoglossal and glossopharyngeal Nerves are seen only cylindrical tubes.
It is a remarkable proof of the difficulty of microscopical observation, that much, if not the whole, of this varicose or moniliform appearance in the nervous matter is called in question by other observers. Valentin, for instance, regards it as the effect of pressure or some similar force; and Henle is disposed to regard the appearances as probably chiefly dependent on chemical changes.
The nervous content or medulla, he remarks, is a tough, soft substance, which may be squeezed out by pressure, and must therefore be regarded as in some degree fluid. In the recent nerve, it appears to be quite homogeneous, and takes its peculiar form under particular circumstances.
As no good analysis of nervous matter has been given, Henle takes as equivalent the analyses of cerebral matter made by John, Vaquelin, Denis, and Couerbe. The essential result of all these researches is, that a saponaceous and a free fatty substance is found in connection with albumen and water in the nervous medulla. During life, and at the temperature of the body, this is an actual solution, not an emulsion; because in an emulsion the fat is only in a state of minute division, and contained in microscopical globules. But the nervous matter is only separated into globules after death; and even then not pure fat globules are formed, but only fat-like globules; and this probably is caused by the separation of the fat and albuminoid constituents.
Under the microscope this nervous matter forms globules which run together in irregular figures. The dark edge is thus rendered broader, and advances on all sides towards the axis of the nervous chord, and at length fills the whole tube. This is covered by granules and irregular lines, which gradually increase, and thereby give the nervous medulla a fine granulated aspect. Similar changes take place, though more quickly, in the nervous matter, when it springs from a wound or lacerated opening in the sheath; there are then formed irregular granular masses, or it retains the cylindric shape which it had in the sheath. The same process is observed in the fine nerves, though less distinctly.
When the nervous tubules are subjected to pressure or stretching, previous to the action of chemical coagulating agents, there are formed oval swellings, and between these shrivelled puckering, often with great regularity. By continuing the force, the oval swellings are converted into globules which are connected by thinner cylindrical portions. In this manner, says Henle, are formed the varicose swellings, that is the bead-like figures of the nerve fibres, which have been much mentioned since the descriptions given by Ehrenberg. He adds, that from any tough viscid matter, from mucilage, saliva, or albumen, it is possible to manufacture similar varicose fibres, by drawing the substances to a thread between the tips of two fingers. There is even an instant at which the thread is changed into a row or string of globules, and so remains until it is torn asunder.
It thus appears that the moniliform aspect and arrangement is the conjoined result of the physical and chemical properties of the nervous tubular content, and of certain mechanical treatment.
Müller, on the other hand, allows that the nervous matter and the cerebral matter has a great tendency to assume the varicose and moniliform arrangement.
From the statements now made only one conclusion can be deduced. This is, either that the minute atomical arrangement of nervous matter is such that it eludes microscopical research, and is placed beyond the boundary at which correct representations can be obtained; or that hitherto microscopical research has presented results so variable, and so discordant, that they convey little useful information. The greater part of microscopic anatomy is still in a state of great imperfection.
Soon after death, and particularly soon after treatment with cold water, there is formed in large nerves, along each edge, a second parallel-running dark line, which first arises quite close to the outer margin, and gradually turns inward from the same. Each fibre is therefore bounded by two dark outlines on each side; at the same time transverse streaks and wrinkles appear on the fibre, by which it has the aspect of a ligament. The two dark lines on each side are not quite continuous; they are often in one single point, below which, within or without, arises a new point, which is quickly split into two parallel lines, or meet with each other, forming, by inclosure, round or oval figures. This twofold outline is seen only in nerves of a certain size. In fine nervous fibres which swell only at certain points, this is seen only at the swellings. Very frequently, it may be said according to Henle, normally, coagulation, beginning from the margins, does not reach the axis of the nerve tube; and there is left in the middle a clear stripe which looks like a cylinder drawn along the length of the nerve-tube. This is sometimes straight, sometimes tortuous, and follows not exactly the outline of the outer margin. Often it lies closer to the one margin, or it draws near to it at one part of its course. This is seen equally in thick and in delicate tubules; in the former more distinctly; it is particularly remarkable when the external nervous medulla is coagulated uniformly, and in fine grains. This streak is the Cylinder Axis of Purkinje, who considered it to be the same with a structure previously described by Remak under the name of Primitive Band. Its diameter is variable; but often it is seen very much the same in nervous fibres of like diameter, that is, about one-fourth to one-half the size of the diameter of the whole tube. When the cut section of a nerve is turned to the eye, this clear streak appears in general round or oval, often irregular, triangular, or quadrangular. This streak is seen also to be bent like a hook or a shepherd's crook, and upon pressure it may be made straight. In some instances the coagulated parts are dissolved, and the clear substance remains with its dark outline as a pale soft isolated thread.
From all these circumstances, Henle concludes that the Nervous fibre consists of a cortical or outer and a medullary substance, which are chemically different.
It appears, however, doubtful whether the central streak (Cylinder Axis of Purkinje) is always present, and is always to be considered as a substantive and real formation; at least, Henle allows, that similar illusive formations arise from quite a different source.
The Cylinder Axis is not in all instances so regular as it is represented in the examples selected. Sometimes it is seen swelled in certain points, sometimes very much attenuated, often altogether interrupted, consisting only of a row of oblong drops, which after being discharged assume a globular shape. Often the coagulated substance extends far beyond the middle of the tubule; the central stripe is then quite irregular, jagged, corresponding to the outline of the coagulated substance. In short, Henle is inclined to the opinion, that this alleged cylinder axis of Purkinje, is a fluid which has become coagulated either after death or by reason of chemical changes. He remarks, that in nerves which have been stretched but not subjected to coagulating agents, the medullary matter is frequently formed into individual oval necklace-like globules connected with each other in rows, and which are thus connected throughout the whole streak. This, he thinks, would not be possible, were the medulla a solid cylinder. If a part of the medulla, he adds, escape through a lateral rent, often, also, there takes place in the matter protruded a discoloration of the central stripe, which is gradually lengthened, and often at its apex is parted into individual globules; a sure proof, he thinks, that the cylinder axis is in this instance fluid. Other similar proofs he adds. It seems to us doubtful whether the point is of sufficient importance to enter into further detail. It is enough for readers to know that this Cylinder Axis, or central portion of the nerve tube, is a sort of hypothetical part inferred to exist from certain microscopical phenomena, but the existence of which, as a fluid or as a solid, the result of certain changes, is at present problematical. Henle allows that amidst so many sources of illusion, it is difficult to arrive at any certain results regarding the cylinder axis.
Kolliker is of opinion that the Cylinder Axis is not an artificial formation, but a substantive part of the nervous chord; and adduces various reasons in proof of his opinion. These, however, it is unnecessary here to consider.
The Gray, Soft, or Organic Nerves, evince their peculiar characters most distinctly in the roots of the Sympathetic Nerve, especially in those branches which, accompanying the internal carotid artery, proceed from the superior cervical ganglion to the fifth and sixth pairs of cervical nerves; and on the branches which proceed downwards from the same ganglion upon the carotid artery.
These nerves are reddish gray in colour, gelatinous, transparent, but tolerably firm. The transverse stripes are not wanting in them; but they are not easily distinguished, are close, and proceed only from the inflections of the Neurilema.
According to Henle, this Neurilema has an external layer of longitudinal filamentous tissue, like that of the White Nerves. But upon the external layer follows a very dense layer of annular fibres, which resemble the filamentous fibres of the embryo, taken during the period of development. These are very clear, apparently homogeneous, flat fibres, from 0.002 to 0.003 of one line in breadth, with numerous round and oval cell-nuclei placed mostly on the flat surface, and arranged at intervals, many of which show the regular nucleus-corpuscula, and not a few are drawn out at both poles into apices. The oval nuclei are in the longest diameter 0.003 of one line. When the nuclei are oval or are elongated into fusiform corpuscula, their long diameter lies parallel to the long axis of the Nervous Fibre, and consequently at right angles to the long axis of the Nervous Bundle. The more the nuclei are elongated and attenuated, the weaker is the connection with the bundles, the more easily it is dissolved, especially after employing acetic acid, from the bundles; and then they roll together or are twined in a serpentine manner. This is best seen in the smallest branches of the Nerve Mottes, which can be placed without injury upon the object-holder and observed by a powerful lens.
In the Gray Nerves are observed two sorts of longitudinal fibres. The one set differ in no respect from the primitive tubules of the White Nerves; they belong, however, for the most part, to the finest nerves, and are accordingly slightly varicose or moniliform. The other set resemble the fibres of the annular layer of the Neurilema; and in them a division of the fibres into fine fibrils occasionally takes place.
On the relative proportion of the two sorts of fibres depends, according to Henle, the external appearance of the gray nerves. The greater the number of the peculiar nerve-tubules, the closer is their likeness to the animal nerves. In the roots of the Sympathetic Nerve, the nerve tubules are present in proportionally small numbers. They lie detached and at distances of from 0.013 to 0.018 of one line, so that between every four and six of the nucleus-covered fibres a nerve-tube follows. In this manner every nerve-fibre appears to be surrounded by fibres of the second sort, because the nerve presents upon every longitudinal section nearly the same figure. But in what relation the nucleus-covered fibres with their surfaces stand to the nerve-tubes is, to Henle, not clear.
More numerous than in the roots of the great Sympathetic are the Nerve Tubes in the greater part of the Nerves of the Viscera, in the branches which proceed from the Celiac Ganglion, from the hypogastric plexus, and similar foci. In these we easily find within the gray branches, the primitive, several beside each other, forming secondary bundles. Nevertheless, their number is more considerable in the chord of the Sympathetic and in the Splanchnic
---
1 Henle, Allgemeine Anatomie, seite 629. General Nerves. The Nerves of the heart have scarcely any but Nerve-tubes. These, as all those proceeding from the Sympathetic Nerve, are distinguished from those of the voluntary muscles by their tenacity only.
Nervous tissue, like all others, receives a proportion of what may be denominated the systems of distribution—cellular tissue and bloodvessels. In the substance of the former, the disposition of which we have already remarked, we find the more conspicuous branches of the latter distributed. In a more minute and divided form they penetrate the neurilema and nervous substance. Reil, who derived his conclusions from the result of delicate and successful injections, perhaps overrated the quantity of blood which in the sound state they convey; for it is quite certain that, in the healthy state, hardly any red blood enters the nervous tissue, as may be easily shown by exposing the sciatic nerve of a dog or rabbit.
No good chemical analysis of nervous matter has yet been published. Every chemical examination of it has been conducted on the assumption that it is analogous to cerebral matter. Of this, however, there is no direct proof. In the analysis by Vauquelin, the neurilematic covering appears not to have been detached—a proceeding always necessary to obtain correct results in this inquiry. The effects of acids and alcohol show that it contains albuminous matter; but beyond this it is impossible at present to make any precise statements.
This description may communicate an idea of the structure of the nervous chord in general. In particular situations this structure is considerably modified. The modifications to which we allude occur under two forms—ganglia (die Knoten), and plexuses (die Nervengeflechte).
Every ganglion consists essentially of three parts,—1st, an exterior covering; 2d, a collection of minute nervous filament; and, 3d, a quantity of peculiar cellular or filamentous texture, by which these filaments are connected, and which constitutes the great mass of the ganglion.
The ganglia are of two kinds, the spinal or simple, and the non-spinal or compound. These two kinds of bodies differ from each other,—1st, in the situation which they respectively occupy; 2d, in the kind of envelope with which they are invested; 3d, in the mode in which the nervous filaments pass through them and from them. By Wutzer, who considers the ganglion of Gasserius, the ciliary and the maxillary of Meckel, as cerebral ganglia, they are divided into three sets, those of the cerebral system, the spinal system, and the vegetative, or those connected with the organs of involuntary motion.
Void of the dense strong coat with which the others are invested, the cerebral ganglia consist of soft secondary matter, connected to the filaments of one, or at most two branches, and are arranged with less complexity (Wutzer).
The spinal ganglia are said to possess two coverings, one of which resembles the hard cerebral membrane (meninx dura), the other the soft cerebral membrane (meninx tenuis, pia mater). The non-spinal or compound ganglia have also two coverings, which are merely different modifications of filamentous tissue, less dense and compact than in the former. Both these sets of ganglia being by maceration stripped of their tunics, and deprived of the soft, pulpy, cellular matter, are resolved into an innumerable series of nervous threads, most of which are minute and scarcely perceptible: all are continuous with the nerve or nerves above and below the ganglion. It appears that the nervous chord, when it enters the one apex of the ganglion, begins to be separated into its component threads, which diverge and form intervals, between which the delicate cellular tissue is interposed; and that these filaments are subsequently collected at the opposite extremity of the ganglion, where they are connected with the other nerve or nerves. Scarpa, to whom we are indebted for most of the knowledge we possess on this subject, compares the arrangement to a rope, the component cords of which are untwisted and teased out at a certain part. Lastly, in the simple ganglia, the filaments of which they consist invariably follow the axis of the ganglion; but in the compound ones they are found to rise towards the sides and emerge from them; and upon this variety in the direction and course of these filaments depends the variety of figure for which these two orders of ganglia are remarkable. These nervous threads (stamina s. fila nervosa) according to Scarpa, correspond to the medullary filaments (fila medullaria) of Wutzer. According to this anatomist, these filaments, when about to enter the ganglion, lay aside their neurilem; yet they are sufficiently tough to resist a certain degree of tension.
Wutzer mentions a cluster of vesicles or cells (cancelli) in the filamentous tissue of the ganglion; but he was not enabled by any means, mechanical or chemical, to ascertain their exact nature.
Probably the explanation of the nature of these vesicles or cells is to be found in the structure described by Henle. According to this anatomist, if, by means of two needles, a portion of a ganglion be torn and pulled to pieces, we find in the water in which the preparation is washed, a quantity of very peculiarly shaped corpuscula, which have received the name of ganglial globules, though only rarely are they globular. More frequently they are ovoidal, triangular, quad-globules, angular, prismatic, kidney-shaped, wedge-shaped, often even quite irregular. In size these bodies are equally variable. The largest are seen in the ganglia of the cerebral nerves. In the Gasserian ganglion of the calf, Henle found some 0.033 of one line in diameter; the greatest part between 0.022 and 0.027 of one line. In the superior cervical ganglion of the same animal, the majority were from 0.009 of a line and less.
These bodies are distinguished by their reddish-yellow colour and soft consistence.
In all, or almost all, there is seen an exactly round corpusculum, which shines like a drop of fat, and in large and small ganglial globules, has pretty uniformly a diameter from 0.001 to 0.0015 of one line. Concentric with this is observed a very fine-drawn and exactly circular line.
In all the rolling movements of the ganglial globules, the small glistening somation remains in the centre of the clear circle, and both continue perfectly round,—a circumstance which shows that both are vesiculae, or globules inclosed within each other. The external one is transparent as water, and its diameter is from 0.006 to 0.008 of one line. Their size bears a proportion to the size of the globules.
If we compare the Ganglial Globules with other cells, the outer substance of the same might appear to correspond to the Cell, the clear vesicular part to the Cytoblast, and the glistening somation to the nucleus-corpuscle. One circumstance, however, which contradicts this interpretation, is, that the whole globule, consequently not only the cell, but also the Nucleus and the nucleus-corpusculum, is instantaneously completely dissolved by acetic acid.
On the deposited ganglial globules depends the yellowish colour and the swelling or enlargement of the nerves in the ganglion. These globules lie together in dense heaps; the most regular and rounded at the surface, the polyhedral in the substance of the ganglion.
---
1 De Corporis Humani Gangliorum Fabricio, &c., cap. I. li. sect. 41, p. 52. 2 Anatomiarum Annotationum liber primus de Nervorum Gangliis et Plexibus. Auct. Ant. Scarpa. Between these globules pass the nervous threads or filaments to their destination, part of them unchanged and uninterrupted; while part of them are resolved into their primitive constituent filaments, and wind in multiplied bendings and turnings round the individual globules and heaps of globules.
extended nerve-fasciculi approach each other and form plexuses, in the meshes of which globules are received. Normally, the nerve-fibres keep mostly together in the axis of the ganglion, and are dissociated and follow the winding course more at the surface; because one central nerve-bundle is on all sides surrounded by ganglial globules. In other instances, the globules are in a greater degree accumulated on one side, form an eminence on the nerve in which they are seated, or the nerve-fibres are principally disposed at the surface, while the nucleus of the ganglion consists chiefly of ganglial globules. Henle thinks it probable that in the axis of the ganglion lie those nerve-fibres, which only break through the ganglion in order to run still farther away in the nervous chord; that, on the other hand, the external enclosing filaments of each separate ganglion for separation are fixed.
In the ganglion of the sympathetic nerve with the proper nerve-fibres of the gray nerves the gelatinous fibres are united, and these stand to the ganglial globules in a particular relation. This is, that the fibres of one bundle are expanded in a funnel-shaped fashion, in order to receive a ganglial globule or a row of these globules; then they are united in order to be again imbricated. Thus it is often possible to extract a whole string of gelatinous fibres from one ganglion, which are enlarged like the pearls of a necklace, and contain globules in these enlargements.
For further details on this point, readers are referred to the General Anatomy of Henle, and the fourth book of the second volume of Kölliker, who, in figure 161, page 524, gives a delineation of the ganglial globules and the nerve-fibres in the first thoracic ganglion of the great sympathetic.
The ganglia are well supplied with bloodvessels, derived in general from the neighbouring arteries. The intimate distribution is represented by Wutzer to be the following. The artery proceeding to a ganglion gives vessels to the filamentous tissue, and, perforating the proper coat, is immediately ramified into innumerable minute canals, the first order of which forms vascular nets on the inner surface of the tunic, while the residual twigs penetrate the flocculent texture, and the individual vesicles of the secondary or filamentous matter of the ganglion.
This short exposition of the structure of the ganglia shows the mistaken notions of Johnstone, Unzer, Bichat, and others, on the structure and uses of these bodies. 1st, The idea, first advanced by Johnstone and Unzer, adopted by Metzger, Hufeland, Prochaska, Sue, and Harless, and afterwards applied with so much ingenuity by Bichat, that the ganglia are so many nervous centres or minute brains, is disproved by strict anatomical observation. 2nd, That they are connected with the order of involuntary actions, and influence these actions, is not improbable; and has acquired a certain amount of verisimilitude from the facts and arguments adduced by Bellingeri, Charles Bell, Herbert Mayo, Longet, and other inquirers. Ganglia are not observed in any of the nerves proceeding to organs of voluntary motion. Sensation, circulation, nutrition, and secretion, are the functions over which they preside, or at least with which they are associated; and they seem to have considerable relation with, if not influence over, the involuntary motions. By some physiologists again this doctrine is limited and modified; and the sympathetic especially has been several times represented as a nerve pertaining solely and exclusively to the nutritious nerves. This, however, leads to the question of the exact functions of the gray or soft nerves, and globules, cannot be considered in this place. 3rd, Lastly, we remark, as a circumstance of some importance, that the only difference between a ganglion and any other part of a nervous chord is, that in the former the minute nervous filaments appear to be uncovered with neurilema, and lodged in a mass of cellular tissue, which is inclosed in the neurilematic capsule; while in the latter each nervous filament has its appropriate neurilema, and the cellular tissue, instead of being within, is on its exterior, and connects it to the contiguous filaments.
In various situations two, three, or more nervous trunks or chords mutually unite by means of some of their component threads, and after proceeding in this manner for a short space, again separate, but not in the same number of original trunks, or preserving the same appearance. In general, the number of chords into which they finally separate is greater than that of which they consisted before union. Three or four nervous trunks, for example, after uniting in this manner, will form on their final separation five or six nerves or nervous chords; and it is quite impossible to determine which of the latter order was derived from any one or two of the former, or what number of individual chords it has received from each. Between the two points, also, the first point of union and the last of separation, many of the more component threads are detached from two or more of their trunks, and, after first uniting with each other in an indistinct network, are again united to two or more of the nervous chords near the point at which they finally separate from the further end of union. This arrangement has been termed a plexus, plait, or weaving, in consequence of the manner in which the nervous chords are interlaced or plaited together. The arrangement which we have noticed as consisting of the more minute nervous threads has been called a smaller plexus (plexus minor). It is a subordinate plexus within a larger one.
The best and most distinct example of a plexus is that commonly named the brachial or axillary. This, as is well known, is situated in the space contained between the broad dorsal muscle (latissimus dorsi) behind, and the great pectoral muscle before, and is formed in the following manner. The fifth, sixth, seventh, and eighth cervical nerves, and the first dorsal, after following the usual connections (ansa), pass downwards from the vicinity of the vertebrae between the middle and anterior scaleni muscles, and, nearly opposite the lower margin of the seventh cervical vertebra, or about the level of the first rib, begin to be united by the component threads of each nerve. Threads of the fifth and sixth cervical unite, sometimes to form a single chord, in other instances to be connected a short space onward with threads of the seventh cervical in a similar manner. The seventh and eighth form two kinds of union. When the seventh is large, it divides almost equally into two chords or branches, one of which is connected first with the fifth and sixth, afterwards with the eighth, and with the first dorsal by interlace ment of minute nervous threads. The other either passes downward to form one of the separate brachial nerves, or is also connected with the eighth cervical and first dorsal in a plexiform manner.
From this arrangement immediately arise the individual
---
1 Mikroskopische Anatomie oder Gewebelehre des Menschen. Von Dr A. Kölliker, Professor der Anatomie und Physiologie in Würzburg. Zweiter band. Leipzig, 1850. Large 8vo, § 124, seite 544. 2 De Corporis Humani Gangliorum Fabrica, &c., cap. ii. sect 41. General nervous branches which form the nerves of the arm, and which are named brachial nerves. The interlacement of minute nervous threads between the seventh and eighth cervical and the first dorsal, is what Scarpa has termed the plexus minor. He says it is peculiar, in being quite uniform, and in connecting those nervous branches which, from their subsequent destination, are called median and ulnar.
This description, though not generally applicable, will communicate some faint idea of the nervous unions and interlacings termed plexus or webs. For more minute information on the distribution, arrangement, and configuration of this part of the nervous system, we refer to the work of Scarpa already quoted.
Henle thinks that we may distinguish the Plexuses into two orders; the first, those in which the nervous trunks send mutually branches to each other; the second, those in which, simply placed beside each other, they lie for a long tract inclosed in one common sheath, and then divide again into different branches. The first kind Kronemberg names Plexus per anastomosim; the second, Plexus per decussationem. The last author adds a third; that, namely, in which both modes of arrangement are united, Plexus Compositi.
Plexiform arrangements are not confined to the exterior regions of the body. They are more numerous internally; and almost all the organs of the chest and belly have each a plexus, sometimes two, from which they derive their nervous chords.
Plexiform arrangements are generally situate in the neighbourhood of bloodvessels, and in some instances inclosing considerable arterial trunks more or less accurately. Thus the axillary plexus surrounds the axillary artery. The celiac artery is surrounded with the solar plexus; and the coronary, hepatic, splenic, superior mesenteric, and renal, are also surrounded with plexiform nervous filaments. In some instances these nervous filaments are so intimately connected with the arterial tubes as to lead some anatomists to consider them as forming a peculiar network surrounding the vessel, and to exercise great influence on the circulation (Wrisberg, Ludwig, and Haase).
It is remarkable that the structure of the nervous chords which form a plexus has either appeared so simple as not to demand particular attention, or is so obscure as to be never noticed. Have the nervous chords and threads in such situations their usual envelope? Is the nervous matter in the chords quite the same as in other situations? Are there any other means of union, save the nervous substance itself?
We believe there is no doubt that every chord in a plexus is provided with its neurilema, as in other places; but this neurilema is generally thinner and more delicate, and the general neurilema seems to be wanting. Its mechanical properties of cohesion and resistance have not been examined.
The view now given of the structure and arrangement of the nervous plexus leads Scarpa to consider them as nearly allied to ganglia. The same separation of the component threads or filaments of the nerve or nerves, the same interlacement, and the same or similar formation of new chords, appear to take place in both orders of structure. A ganglion, indeed, he conceives, is a condensed or contracted plexus; and a plexus is an expanded or unfolded ganglion.
The anatomical purpose of both appears to be simply a new arrangement or disposition of nervous branches, previous to their ultimate distribution in the tissues or organs to which they are destined. This is nothing but the expression of a fact,—the interpretation in intelligible terms of an arrangement of organized parts, without reference to any supposed uses.
I have already shown what is meant by the organic end or termination of a nerve. Although the nervous trunks are distributed in every direction through the animal body, they do not terminate in all the tissues or organs indiscriminately, and have been observed to be lost in the following only:
1st. The proper organs of sensation, the eye, ear, nose, palate, and tongue; 2dly, the muscles, whether subservient to voluntary or to involuntary motion, as the heart, stomach, intestines, &c.; 3dly, the mucous surfaces; 4thly, the skin; 5thly, glands, salivary, liver, kidneys, &c.; 6thly, bones.
Nerves, therefore, are not organs of general distribution. According to Bichat, they have never been traced to the following tissues—the cartilages, both articular and of the cavities; fibrous textures, viz. periosteum, dura mater, capsular ligaments, aponeurotic sheaths, aponeurosis in general, tendon, and ligament; fibro-cartilaginous textures—those of the external ear, nose, trachea, and eyelids (cartilages of other authors); the semilunar cartilages of the knee-joint; those of the temporomaxillary articulation; those of the intervertebral spaces; marrow; the lymphatic glands.
To this we may add the testimony of Walter of Berlin, who, after several laborious researches, came to the conclusion that the pleura, the pericardium, the thoracic duct, and the peritoneum, receive no nerves, and that, contrary to the opinions of the most eminent recent anatomists, no nerves terminate in the lymphatic or conglomerate glands. Sometimes, indeed, these organs are perforated by one or two twigs, as he often had occasion to observe; but they instantly proceed to the next place assigned to them, and in which they are finally lost. If, after this conclusion of Walter, personal testimony can be of any use, I may add, that I have examined the dura mater, the periosteum, and most of the synovial membranes repeatedly, to discover nervous filaments in them, and always without success; and I may say the same regarding the absence or non-appearance of nerves in the peritoneum and pleura.
The nerves have different uses in the different organs and tissues to which they are distributed. 1. In the organs of sensation they receive the material impressions made on the mechanical part of the organ. In the mucous membrane of the nasal passages, the filaments of the olfactory nerve are affected by aromatic particles, dissolved or suspended in the air. In the eye the retina receives the last image formed by the transmitting powers of the transparent parts. In the ear the terminations of the auditory nerve are affected by the oscillations or minute changes in the fluid of the labyrinth, occasioned by the motions of the tympanal bones. In the palate, tongue, and throat, the gustatory nerves are affected by sapid bodies dissolved in the mouth, or applied in a fluid state to the mucous membrane of that cavity. 2. In the system of voluntary muscles, the nerves retain the action of the muscular fibres in a state of uniformity and equality, and keep them obedient to the will. In the involuntary muscles they appear merely to keep their action equable, regular, and uniform; and in both they maintain a communication, consent, or harmony of action between different parts of the same system of organs, or even between organs concurring to the same function. 3. In the glandular organs the nerves certainly exercise some influence over the process of secretion; but what is the exact nature of this influence, or in what degree it takes place, is quite uncertain.
When we observe the nerves distributed to organs of sensation and organs of motion, it is a natural thought to inquire whether the nerves minister to both functions, and whether different nerves or different sorts of nerves minister to each function. It seems to have been an idea of considerable an-
---
1 Annotation. Anatom. cap. iii. sect 9, p. 94, 95. 2 Prof. Tab. Nerv. Thoracis et Abdominis, J. G. Walter. Berolini, 1783. tiquity, that one set of nerves are sensiferous, and another set motiferous. Erasistratus derives the nerves of motion from the brain and cerebellum, and those of sensation from the membranes; and Galen distinguishes the nerves into Neopla Alogorhena and Neopla Kavrosa, the former soft, from the brain, the latter hard, from the spinal marrow. This distinction was not altogether lost sight of among the anatomists and physiologists of the eighteenth century; but it was rather maintained as a probable speculation than elucidated and enforced as an established doctrine, pregnant with important results. It was recognised by Glisson, and taught by Boerhaave, and received and promulgated by his pupils, Tissot and Van Eems; but opposed by Haller and Cullen. The distinction was, nevertheless, maintained by Lecat, Morin, and Pouteau, the last of whom was led from various examples of persons, who, after injuries, had lost sensation, but retained the power of movement, to espouse it with considerable energy.
In 1784 George Prochaska, Professor of Anatomy at Vienna, published on the functions of the nerves a commentary, in which he gave, after Haller, Caldani, Whytt, and Unzer, a more precise and correct view of the uses, properties, and powers of these organs, than had hitherto been formed. In this commentary he fully recognises the distinction between sensorial nerves, or those devoted to sensation, and motific nerves, or those ministering to motion; he shows that sensorial impressions, or impressions made on the sensitive nerves, are reflected or transmitted in a reflex direction to the motific nerves; that the latter nerves are thereby excited to action; that the purpose of this reflex operation is the preservation of the individual; and that the whole are under the influence of the Sensorium Commune. He distinctly states, that this reflected action is not regulated by physical laws, where the angle of reflection is equal to the angle of incidence, but obeys peculiar laws impressed by nature, as it were, on the sensorium, and which laws we can understand from their effects alone. This reflex action further takes place either without or with the consciousness of the soul. The motion of the heart, stomach, and intestines, is independent of the cognizance of the soul; and in many other instances of sensorial impressions being transmitted to motific nerves, though the soul is conscious, it can neither prevent them nor promote them.
The commentary of Prochaska is the first precise view of functions of the nervous system in modern times; and the first in which the automatic and instinctive phenomena enumerated by Whytt are referred to a reflex operation.
In 1811, Sir Charles Bell, in a tract containing the Idea of a New Anatomy of the Brain, stated that he had proved experimentally that "the posterior fasciculus of spinal nerves, which are gangliophorous, might be detached from its origin without convulsing the muscles of the back; whereas, on touching the anterior fasciculus with the point of the knife, these muscles were immediately convulsed." From this it seemed a probable inference that gangliophorous nerves had no concern in motion, and that nerves void of ganglion ministered in some way to that function.
In 1818, Charles Francis Bellingeri published at Turin, a Dissertation treating, among other subjects, of the anatomy and physiology of the fifth and seventh pairs of nerves. In this he showed that the great portion of the fifth pair or tracial nerve, which forms the large semilunar plexus called Gasserian ganglion, is a nerve not of motion but of sensation; that its three branches are distributed to certain parts of the eye, the nasal cavities, the palate and tongue; ministering in these parts not to motion, but to sensation, and probably to circulation, nutrition, and secretion; and that the small branch of that nerve (nervus masticatorius) is distributed to muscles (temporalis, masseter, pterygoideus, buccinatorius), and is a nerve of motion. He also showed that the seventh pair, or lateral facial, presides over sensation and motion in the functions of the head, face, and neck, but mostly over motion.
In 1821, Sir Charles Bell undertook to establish the principle, that of the two nervous trunks distributed to the face, viz., the trigeminus, or fifth cerebral nerve, and the portio dura, or seventh cerebral nerve, the lateral facial, the former presides over the sensations or common sensibility of the head and face; that it also possesses branches going to the muscles of mastication; whereas the latter nerve regulates the muscular motions of the lips, nostrils, and velum palati, and especially in associated action with the motions of respiration.
About the same time Magendie claimed the merit of showing experimentally the fact of the distinction between nerves ministering to sensation and nerves ministering to motion, and of proving that, of the double row of nervous roots issuing in parallel lines from the lateral regions of the spinal chord, the anterior are destined for motion, and the posterior for sensation.
Lastly, Mr Mayo, partly by dissection, partly by experimental inquiry and reasoning, arrived at the conclusion that almost all the branches of the large or gangliophorous portion of the tracial nerves are nerves of sensation, while those of the small fasciculus, which is void of ganglion, are nerves of motion.
In this manner, by successive steps, has been established one of the most important doctrines on the functions of the nervous chords in modern physiology; and its justice has been confirmed by the labours of many observers. The distinction is most clearly proved by the original experiment of Sir Charles Bell. If the spine be laid open, especially in a cold-blooded animal, as a frog, and the posterior or gangliophorous roots alone be irritated, no movement is produced; but the moment the anterior roots are touched, the extremities are agitated by active convulsive motions.
---
1 Praelectiones Academicæ in proprias Institutiones Rei Mediceæ, Editæ et Notis Auctæ, ab Alb. Haller. VII. Tomi. 12mo. Goettlingæ, 1745. 2 Hermanni Boerhaave, Phil. et Med. Doct., &c. Praelectiones Academicæ de Morbis Nervorum, Quas ex Manuscriptis collectis edit curavit Jacobus Van Eems, Medicus Leydeniensis. Tome I. and II. Lugduni Batavor. 1761. "Omnes (nervi) inserviant motui vel famulantur sensui; sed in illis qui cordi, pulmoni, hepatis, alisque partibus vitalibus destinati sunt, sensus non deprehenditur. Qui motui inserviant, absunt ad musculos, et in illo molliscent, ut in verum quasi cerebrum degenerent. Ramuli, qui sensibus famulantur, in ipsis organis mollitie fere diffundant, ut patet in expansione nervi opticæ, olfactorii, ubi se applicat ad os ethmoides, et acustici in labyrintho," p. 291. 3 Elementa Physiologica, Liber X. Sect. VIII. § xxiii. Tomus Quartus. p. 389. 4 Mémoire et Recherches sur la difference à établir entre les nerfs du sentiment et les nerfs du mouvement, à l'occasion de quelques observations sur cette espèce rare de paralysie, qui prive un membre de tout sentiment, sans lui ôter l'usage du mouvement. Ouvres Postumes de M. Pouteau, Docteur en Médecine et Chirurgien en Chef de l'Hôtel-Dieu de Lyon. Tome II. p. 480. Paris, 1789. 5 Georgii Prochasku, M.D., Professoris Anatomiae, Physiologiae et Morborum Animalium in Universitate Vindobonensi, Operum Minorum. Pars II. Vienne, 1800. Svo. Commentatio de Functionibus Systematis Nervosi. 6 Caroli Francisci Bellingeri E. S. Agatha Derthonensi. Phil. et Med. Doc. Amplissimæ Med. Collegii Candidati Dissertatio Inauguralis quam publice defendebat. In Athenæo Regio Anno MDCCCLXXXVIII. Die IX. Maii; hora IX. ma mututina. Auguste Turinorum. 1818. Ex Anatomia; De Nervis Faciei; Ex Physiologia; Quinti et Septimi Paris Functiones, &c. Of the cerebral nerves, the first or olfactory, the second or optic, and the eighth or auditory, are pure nerves of proper sensation, and are distributed to the sensitive parts of the eye, the nasal cavities, and the cochlea and labyrinth, respectively. The third, fourth, and part of the sixth, or abducent, are motific nerves connected with the movements of the eye. The fifth or tracial is a very peculiar nerve. The gangliophorous, or rather plexiform part of it, communicates with all the organs of proper sensation,—the eye, the ear in a small degree, the nasal cavities largely, and the palate, mouth, and tongue largely; and it is distributed extensively along with the minute arteries of the face. Of this arrangement the result is, that it is a nerve neither of vision nor of hearing, of smell nor of taste, or deglutition nor of touch, or physiognomical expression, exclusively; but over the whole of these faculties and their proper organs exercises a general modulating power. It maintains between them a mutual consent or harmony of action, absolutely necessary to the due separate exercise of each and the conjoined exercise of all. Lastly, by accompanying the arteries of the face, it regulates the circulation of that region, and may be the means of maintaining between the brain and the facial circulation those conditions and expressions which arise from various mental emotions; as paleness, blushing, indignation, the sense of joy, triumph, the sublime, and similar emotions.
Not less peculiar is the seventh, the small sympathetic of Winslow. Though mostly a motific nerve, yet it ministers to motions of a particular order. It is, however, as a nerve distributed to the skin of the face, a nerve contributing to, if not regulating animal sensation and involuntary motion. It is, in fact, as shown by Wrisberg, a double nerve, the large portion of which is devoted to the purposes of animal life, and the small one to those of organic life. It is a musculo-cutaneous nerve of the head and face.
In proceeding further in explaining the respective functions of the nerves, it is requisite to keep in view not only their gangliophorous character and the reverse, but their position as anterior and as posterior nerves, and nerves consisting of anterior and posterior roots.
The ninth pair (nerveus glossopharyngeus), consists of two parts, one large, completing sensation to the root of the tongue and pharynx, the other smaller, moving the pharynx, and connected, notwithstanding, with the tenth pair, pneumogastric, and the great sympathetic.
The tenth pair (nerveus vagus), or pneumogastric nerve, is chiefly a sensiferous nerve, regulating the sensations of the larynx, the oesophagus and stomach, and the lungs, and placing these organs in harmony as to function. One particularly, the recurrent branches, appear to be motific. All the other branches appear to regulate circulation and secretion.
To the accessory nerve, or eleventh pair, seems to belong the function of placing the pulmonary and laryngeal divisions of the pneumogastric in harmony and relation with the external muscles of the back and lateral regions of the neck.
Lastly, the hypoglossal, or twelfth pair, having mostly an anterior origin, are motific. They form the motific nerves of the muscles of the tongue.
It is to be observed, nevertheless, that though this distinction in functions belongs to particular nerves, yet nerves ministering to sensation, and regulating organic or involuntary functions, and nerves ministering to motion, and regulating either voluntary motions, instinctive motions, or involuntary but associated and necessary motions, are often closely connected, and proceed together in the same sheath, or in close apposition, to the same organ. This, which is observed in the fifth, the seventh, the ninth, tenth, and eleventh, is rendered necessary by the offices which the organs have to perform. The impulse or impression is communicated to the organ, and received by its sensiferous nerves. By these the proper sensation is transmitted, and the motific nerves are excited to action. This appears to be the mode in which such actions as sneezing, coughing, yawning, deglutition, and numerous other instinctive and associated actions are called into operation.
Of the spinal nerves it is almost superfluous to speak, after the explanations now given. The splanchnic or great sympathetic appears to be a nerve of organic sensibility and impression, and as such regulates the circulation of the abdominal organs, and transmits their impressions to the central connections. The further continuance of these by its spinal connections establishes a harmonic action with the spinal marrow, always for good purposes, but often under disease producing painful and destructive effects.
The doctrine of reflected action in the nervous chords, as proposed by Prochaska, was either overlooked, and more or less disregarded; or it was thought that the phenomena referred to it were explained, as far as was practicable, by the doctrines of Robert Whytt and Haller. At the same time it was taught by Prevost and Dumas in 1823, that in what is called nervous action, or the operation of nervous influence, there must be, as in galvanism, two currents, an ascending and a descending one; the former proceeding from the ramified to the central end of the nerve, the latter from the central to the ramified or distributed end. In 1826, Sir Charles Bell, in a paper read to the Royal Society, promulgated the general proposition, that, between the Brain and the Muscle, there is a circle of nerves; one nerve conveys the influence from the Brain to the Muscle; another gives the sense of the condition of the Muscle to the Brain.
In 1833, Dr Marshall Hall communicated to the Royal Society a paper on the Reflex Function of the Medulla Oblongata and Medulla Spinalis, in which he undertakes to demonstrate the existence of reflected or retrograding nervous influence, that is, one which proceeds from the ramified, or distributed to the cerebral or cerebro-spinal extremity of the nerve. According to the hypothesis here propounded, the spinal chord is the seat and centre, as it were, of two processes taking place in living animals. It receives sensations caused by impressions on the extreme points of the nerves; and, in consequence of this, it induces or stops actions on certain muscles and muscular organs. An impression acts upon the distributed extremity or extremities of a nerve; this is instantly conveyed by the nerve to the spinal marrow; and in the same instant, the spinal marrow either causes movement, or retains in a fixed state certain muscular organs. As this action or process consists of two parts, an incident impression, and a reflected one causing motion, it was denominated the Reflex Function of the Spinal Marrow; and as it consists in impression supposed to excite or cause movement, it was named by its proposer, excito-motory, and the nerves by the agency of which these movements were induced he denominates Excito-Motory Nerves.
According to Dr Marshall Hall, there are two orders of Nerves. Incident Nerves, proceeding principally from the Cutaneous surface, and the surface of the Mucous Mem- branes to the Spinal Marrow; and Reflex Nerves passing from the Spinal Marrow to a series of muscles destined to be moved simultaneously; and he thinks that he has proved the existence of, 1st, an incident motor action, and, 2d, an incident motor nerve.
The incident motor branches are those of, I. The Trifacial nerve; II. The Pneumogastric; III. The Glossopharyngeal; and, IV. The Posterior Spinal nerves. To these there are corresponding reflex branches; and in the centre between the two, according to the doctrine, is placed the Medulla Oblongata and the Spinal Marrow, as the recipient of impressions and the generator of movements.
Under this system of nerves and nervous movements are placed all the great functions of the animal body; respiration; the acts of ingestion and egestion; the action of the uterus during parturition, and all those movements the object of which is the preservation of the individual from injury, whether arising within the system, or approaching from without.
It is unnecessary here to express upon the merits of this hypothesis any opinion. Its true character is that of placing facts long known and observed, under the head of a doctrine, new, and, it may be, more intelligible and tangible than the former. It is, nevertheless, still in the condition of a hypothesis, though a probable and convenient hypothesis. The further consideration of the subject belongs to the department of physiology.
It may have been observed, that, in speaking of the properties and uses of the nerves, as living and organized textures, we have been obliged to employ various terms which are in common use when speaking of the properties and uses of the nervous system; for instance, Sensibility, Impressions, Sympathy, Irritability, and similar denominations. These terms it would have been desirable to define with as much precision as the imperfections of language and the nature of the subject allow. This part of the subject, however, properly belongs to the doctrine of the functions of the living body, and as such it shall be considered under the head of Physiology.
In the fetus the nerves are developed with remarkable perfection. I cannot speak from personal observation much earlier than the sixth month, when I have found the nerves of the extremities and voluntary muscles large and distinct. At the eighth month they are still more conspicuous. The anterior crural nerves are in the form of flat white cords, one and a half line broad, and their branches like good-sized threads. The sciatic is still more distinct. In the form of a thick cylindrical cord, fully a line in diameter, and not unlike a piece of whipcord, it is tough, stringy, and resists tension; and its constituent threads are well marked. I immersed a portion of this nerve, three and a half inches long, in aqua potassae, when it first became much firmer and denser than before, assumed in two days the satiny fibrous appearance first described by Fontana, and at length by solution of the nervous matter, was separated into chords and neurilematic canals. In this state, preserved in spirit of turpentine, it conveys a tolerably correct idea of the arrangement of the neurilematic canals.
The nerves of the involuntary muscles are equally distinct in proportion. Those of the lung, heart, and splanchnic system are distinct and manifest at the eighth month.
The neurilem is much more vascular in the fetus than in the adult. In the same fetus of about eight months I found the neurilem of the sciatic nerve, from the ischiatic notch to its division in the ham, covered with a thick network of minute vessels, all injected with dark blood.
The Nervous Papillae of Vater—The Corpuscula of Pacini.
The limits assigned to this article permit not to consider in detail all the modes in which the nervous extremities terminate in the organs, and the membranous surfaces to which they are distributed. But one mode of termination has, since the year 1834, attracted so much the attention of anatomists, that it would be improper entirely to omit the mention of it. This is what are called the Corpuscula of Pacini.
In the year 1741, Abraham Vater, Professor at Wittemberg, made known the fact that the nerves of the thumb terminate, when traced to their extremities, in round or spheroidal bodies, to which he gives the name of Papillae Nervae, and Papillae Cutaneae. This discovery of the peculiar mode in which the digital nerves terminate, was made known in an inaugural dissection by J. G. Lehmann, one of the pupils of Vater; and the preparation from which the description by Lehmann was formed, has been preserved in the Anatomical Collection of Wittemberg to the present time.
The description given by Lehmann, which must be regarded as virtually that of Abraham Vater, is not very minute. Vater, or Lehmann for him, states that he found in the body of a man who had been affected by a spasmodic attack in the right arm and the middle and ring fingers, the nerves distributed to the thumb terminated in numerous small eminences or papillae, which required to be carefully and laboriously dissected from the fat in which they were inclosed. These bodies he compares to the ears of corn. Vater found papillae of the same sort, in small number, attached to the extremities of two branches of the posterior crural nerve, distributed over the dorsum of the foot. This occurrence took place several years previously to the time, 2d November 1741, at which it was made known. On the exact nature of these bodies Vater gives no opinion, further than is to be collected from his calling them Nervous Papillae, and Cutaneous Papillae, and mentioning them in connection with the consensus of the parts of the human body. It may be doubted whether he was aware of the signification of these bodies even in an anatomical point of view.
The fact now mentioned has been overlooked and neglected for an entire century; and no one seems to have thought it of sufficient importance after the dissertation of Lehmann to deserve mention. At length, in February 1834, M. Camus, in a minute account of the distribution and termination of the nerves of the hand, described, as existing in the palmar and anterior half of the lateral aspect of the fingers, certain minute bodies, opaque, pearl white, not larger than a grain of mustard-seed, attached to the extremities of the digital nerves. Similar minute opaque pearly-looking bodies, M. Camus found attached to the nerves in the plantar aspect of the foot, most numerous towards the roots of the toes, and in general smaller than those found terminating the nerves of the hands.
It further appears that Philip Pacini, a physician in Pistojja, had seen these minute bodies in 1831, gave an account corpuscula of them in 1835 to the Medical Society of Florence, described them in the Nuovo Giornale of Pisa, gave a second oral communication on them, and demonstrated their existence at the Scientific Congress held at Pisa in October 1839. From this circumstance, and Pacini publishing an enlarged
---
1 The Diseases and Derangements of the Nervous System. By Marshall Hall, M.D., &c. London 1841. Page 48-50. 2 Dissertatio de Consensu Partium Corporis Humani. Expositio simul Nervorum Brachialium et Cruralium Coalita et Papillarum Nervearum in Ditis Dispositione. Quam P. Abrahams Vatero pro O. Doctoris Exponet. J. Gottlob. Lehmannus Vittembergae, die 2 Novembris 1741. Apud Haller Dissertiones Anatomicae Selectae. Vol. II. Gottingen, 1747. Page 953. 3 Archives Generales de Medicine. Fevrier 1834. And Edinburgh Medical and Surgical Journal, vol. xlii, 1834, p. 225. General account of these corpuscula in 1840, these bodies have been usually designated as the corpuscula of Pacini, and the Pacinian bodies.
In 1836, they were mentioned by Cruveilhier, though not as essential parts of the nervous system; and they were again described by A. G. Andral.
In October 1843, M. Lacaniche announced to the Academy of Sciences at Paris, that he had found in the mesentery and mesorectum of various animals, especially the common cat, minute bodies which are manifestly the same as those seen by Pacini in the fingers. According to Lacaniche, they are ovoidal transparent bodies, with the long diameter somewhat more than one millimetre. With the aid of the microscope he distinguished a peripheral part formed of from 15 to 20 concentric layers, and a central hollow portion, which extends the whole length of the body, terminates at one apex in a shut end, and at the other communicates by means of a serpentine canal with the nearest lymphatic canals. These bodies have since been described more or less minutely by Mayer of Bonn, Pappenheim, and most of all by Henle and Kölliker, in a monograph in 1844, and by Strahl in 1848.
The Pacinian corpuscula, which must have been often noticed by observers who studied the chyliferous vessels in the cat, were seen by Pacini first in man, and afterwards in cattle. They are seen normally without exception in adults as in the fetus and new-born infants. Usually they are numerous in the nerves of the hand and foot, in the palm and sole. They are besides observed in the sacral plexus, in the crural nerve, in some cutaneous nerves of the upper arm and fore-arm, in the epigastric plexus and nerves issuing from it, and in the neighbouring plexuses. Their number in the whole body must be considerable; and in a single hand from 60 to 200 have been numbered. They are either detached or accumulated in small heaps. In all cases they are attached by one end by a stem variable in length to an adjoining nerve. They are for the most part distinctly visible to the naked eye; elliptical or long-oval bodies of opal lustre; and through the more translucent middle, in the long direction, are observed slightly tortuous streaks. In adults their average length is from $1\frac{1}{2}$ to 2 millimetres. In the fetus they are often so small that either they cannot be seen, or they are seen by the naked eye with great difficulty. At the point of division of the median nerve, and ulnar nerve, in the fingers, and the plantar nerve in the branches going to the toes, they are largest; at the tips of the fingers they are smallest. The stems or peduncles by which these bodies are attached to the nerves join the nerves either at a right angle, or so that they are inclined sometimes more to the central, sometimes more to the peripheral end of the nerve. Not unfrequently two bodies are attached by means of a bifurcated stem. The stems or peduncles appear to be continued backwards in a conical fashion into the corpuscula, by which they are easily distinguished by their transparency from the substance of the rest of the corpuscula. This prolongation amounts sometimes to one-fourth part and more of the entire length of the Pacinian body.
When the corpusculum is examined under the microscope, it presents numerous fine dark lines, which proceed on the outside or along the periphery of the corpusculum by the edges, and within, run parallel to the long axis of the corpusculum, and are separated from each other by clear, broader intervals. At the stalk-end of the capsule (a), the concentric lines incline to each other, and are continued then, as is observed in large Pacinian bodies, in fine dark lines, which may be seen compressed parallel and closely to the stalk. At the free end, on the other hand, the concentric and parallel lines of the corpuscle are united on both sides; yet here there is also often observed a white line penetrating into the interior of the corpusculum, (ligamentum intercapsulare,) which appears to correspond with the prolongation of the stalk on the other side. The fine, closely compressed, parallel lines of the proper stalk become towards the nerve progressively more subtile, and in most cases vanish altogether from the eye before they sink into the nerve. In the middle of a corpuscle there is observed a longitudinal space, more or less transparent, which follows in like manner the longitudinal axis of the corpusculum. The dark lines lying next to it are more numerous, more closely compressed on each other, and run almost entirely straight. These concentric dark lines appeared to the observer as the outlines of so many capsules placed in layers on each other; and this view was confirmed by careful dissection. In short, when the apex of one corpusculum is cut off, there is observed close to the opening a small quantity of fluid, the corpusculum collapses, and from the interior proceeds a new corpusculum, more sharply defined, and smaller and more pointed than the former. This operation may be repeated several times, always with the same phenomena, except that the size of the corpusculum diminishes, and the oval form passes more and more to the cylindrical.
A Pacinian body consists, therefore, of a greater or smaller number of capsules inclosing each other, which are separated General Anatomy from each other by a greater or less quantity of fluid, easily miscible by water. The spaces between the capsules filled with fluid are named by Pacini intercapsular spaces.
The dark parallel lines of the stalk correspond to tubes encased within each other of the sections of the membranes, which tubes are continued into the capsules, yet contain no fluid. The conical prolongation of the stalk within the corpusculum is formed in such a manner that the stalk of the inner capsule penetrates further into the same than the outer. The innermost tube of the stalk proceeds without expansion into the innermost capsule forming the central cavity.
The internal central cylinder Henle and Kölliker compare to the primitive nervous fibre. Henle discovered a nervous fibre in the central canal of the corpusculum.
The accuracy of these observations has been in general confirmed by Strahl, who proposes to restore the original merit of discovery to Vater by calling the bodies Vaterian Corpuscula.
The Capsules which give the Vaterian Corpuscula their peculiar shape vary much in number and width. Usually there exists, as the early observers represent, a system of internal capsules; but this does not always contain the same number of capsules; and the latter are not in all cases smaller than the outer, but often interrupted in consequence of their width.
The capsule walls consist of structureless filamentous tissue, in which are imbedded Nuclei. Fibrous structure Strahl did not recognize even with strong magnifying powers; and at most he only observed a difference of longitudinal and transverse fibres.
Most commonly only one particular nerve-fibre runs into each Vaterian body.
Anatomists are not agreed as to the nature or the uses of these bodies. All that is known is what is now stated; that by one extremity or pole they are connected with the nervous system, and by another with the lymphatic system. As to uses, it seems reasonable to think that in some manner they are concerned in the functions performed by the extremities of the nerve. But on this point there is great uncertainty. They appear not to be particularly connected either with sensation or with the sense of Tact as possessed by the fingers. In the extremities they are observed in spots in which these functions are not expressed with particular energy. They are generally in greatest number in the ball of the thumb; and they are situate in the toes, in parts at which neither sensibility nor Tact can be said to be considerable.
Pacini entertained the idea that they are connected with the development of electricity; and Henle and Kölliker were disposed to favour this opinion. Strahl subjected the opinion to the test of experiment, and arrived at the conclusion that in the Vaterian Papillae no electricity or electro-magnetism can be demonstrated.1
CHAP. II.—THE PARTICULAR TISSUES.
Cerebral System.—Brain. (Cerebrum.)
The brain or central part of the nervous system may be regarded as a continuous organ, consisting of three divisions,—the convoluted, the laminated, and the smooth or fuciculai portions. Of these divisions, which are distinguished according to the peculiar external configuration of each, the first part corresponds to what is named the brain proper (cerebrum); the second to the small brain (cerebellum); and the third to the oblong production contained in the vertebral column, and known under the name of the spinal chord.
The convoluted portion presents two surfaces, an outer or convoluted, and an inner or figurate. The laminated portion in like manner presents two surfaces—an outer or laminated, and an inner or central. The third has only one surface, which is exterior. These different surfaces, and their mutual relations, will be more minutely explained afterwards. At present we shall examine its physical and anatomical characters as an organic substance.
The three divisions of the central part of the nervous system are composed of a peculiar substance which may be denominated cerebral matter, inclosed in delicate vascular membranes. To exhibit the external characters of this substance, these membranes must be removed by careful dissection. When this is done, and the brain is inspected on its surface and after sections, the cerebral matter is observed to vary in colour, consistence, and intimate structure, in different parts of the organ. These varieties of cerebral matter are most easily distinguished, according to their colour, into white and gray or cinereous.
The white cerebral matter is of different shades in different parts of the brain. Its most usual hue is orange-white, or orange-white inclining to reddish-white, or purplish-white. This is most distinctly recognized in the mesolobe (corpus callosum), and in the body named hippocampus major. The consistence of the white cerebral matter is considerable. It is in general more tenacious and cohesive than the gray matter, and when indurated is less brittle.
A section made by a sharp scalpel appears smooth and of a uniform colour, traversed by reddish points and streaks. It presents nevertheless different appearances in different directions. In certain parts, for example the mesolobe, it presents the appearance of minute capillary lines, arranged in parallel juxtaposition, and giving what is named a fibrous appearance. In other regions, however, as in the white matter of the optic chambers, this cannot be recognized.
White cerebral matter has been examined microscopically by Della Torre, Prochaska, the Wenzels, Sir Everard Home, and M. Bauer.
If we trust the observations of Father Della Torre, the white and gray substance of the brain, cerebellum, medulla oblongata, and spinal chord, consist of an aggregation of infinite transparent globules, floating in a pellucid, crystalline and somewhat viscid fluid. The only difference which he admits among the matter of these several parts is, that he represents the globules to be largest in the brain, smaller in the cerebellum, and still more minute in the medulla oblongata and spinal chord. The arrangement of these globules in the central portion of the nervous system he further represents to be promiscuous.
Prochaska placed on a thin plate of glass minute slices of cerebral matter, so thin that they were translucent; and in this state he found it consist of innumerable globular particles, united by delicate, pellucid, flocculent matter, like filamentous tissue. These globules varied in size even in the same part of the brain. In general, however, he found them both in the brain and cerebellum to be rather more than eight times smaller than the globules of the blood. He was unable to ascertain anything regarding their intimate structure.
The Wenzels found the white cerebral matter to consist of very minute globules, or roundish atoms, resembling spherical cells containing proper medullary or white cerebral substance. The dimensions of these globules they did not attempt to estimate; but represent them in general as exceedingly minute, and all of the same size. They could not
---
1 Zu den Pacinischen Körperchen (Papillen). Von A. Vater. Von Dr J. Carl Strahl. Müller's Archiv, 1848. Seite 165. Edinburgh Medical and Surgical Journal. Volume seventy-third, p. 118, 1850. recognize any connecting medium. The globular appearance was retained in portions of brain exposed to the action of alcohol and muriatic acid, and in those even which had been dried after induration in alcohol.
M. Bauer placed a thin slice of white cerebral matter on a plate of glass previously moistened, and allowing a drop of water to fall on it, held obliquely, and thereby to diminish its cohesion, brought into distinct view innumerable loose globules, many fragments of fibres of single rows of globules, and bundles of fibres, some of considerable length.
The use of water in this mode of examination is to dissolve and remove a viscid, gelatinous, semifluid substance, on which the adhesive properties of the white matter seem to depend. If water is not used, the brain adheres to the glass, and the globular appearance cannot be recognized.
These globules vary in size from \( \frac{1}{32} \)th to \( \frac{1}{64} \)th of an inch in diameter; the general or average size being \( \frac{1}{32} \)th. Those of the white matter are largest, that is \( \frac{1}{32} \)th. They are translucent, whitish, and arranged in lines or rows of single globules, which are attached to each other by the viscid semifluid mucus. The strings or rows of globules are connected into bundles or fasciculi by the same medium. There is reason to believe that the translucency of the globules depends on an albuminous fluid, which on immersion in alcohol or acids is coagulated, and thereby rendered opaque.
When a portion of white cerebral matter is immersed in boiling oil, or is steeped for a few days in alcohol, dilute nitric or muriatic acid, or in a solution of corrosive sublimate, it acquires great firmness and solidity, and may be torn or broken like a piece of cheese, which it could not be before, in consequence of its tenacity. Certain parts, for example the mesolobe, appear then to be distinctly fibrous, or to consist of long capillary lines placed in close juxtaposition. On the length of these filaments or fibrils, however, nothing is ascertained. It is also undetermined whether the white cerebral matter is in all parts arranged in the fibrous manner.
White cerebral matter is well supplied with bloodvessels. These, indeed, are minute; but they consist both of vessels containing red and colourless blood. The division of these vessels gives rise to the appearance of red points (punctula) and streaks, which are exhibited on the surface of sections. It is believed to be less vascular than the gray cerebral matter.
On the chemical constitution of white cerebral matter we possess no accurate information; all the chemical analyses hitherto made having been directed to brain, without distinction of its different varieties. From the circumstance, however, of its becoming indurated on immersion in alcohol, acids, and solutions of corrosive sublimate, it is manifest that it contains much albumen. It is rendered yellow by nitric acid. If a portion of indurated brain be placed in the sun, or in a warm atmosphere, an oily or unctuous fluid exudes from its surface, which shows that it contains fatty matter; and if brain be immersed in ether, this fatty matter is partially removed.
The analysis of Vanquelin, which is probably very near the truth, shows that 100 parts of cerebral substance, not distinguishing between white and gray matter, consist of 80 parts of water, 7 of albumen, 4-45 of white adipose matter, 0-70 of red adipose matter, 1-12 of osmazone, 1-5 of phosphorus, and 5-15 of acids, salts, and sulphur. Upon the presence of the albuminous matter depends the solidification which the brain undergoes, when immersed in alcohol, acids, or solutions of the metallic salts, by which albumen is coagulated. Upon the presence of the white adipose matter depends the formation of those brilliant white crystalline plates, resembling cholesterine, observed by M. Gmelin, in the brains preserved in the Anatomical Cabinet at Heidelberg. The opinion of this chemist, that it pre-exists in the brain in the form of adipocerous or cholesterine matter, is to a certain extent probable. The elements, at least, of this matter, that is elaine and stearine, must exist in the brain.
Couper distinguishes in brain four fatty principles, Cerebrot, Eleencephol, Cephalot, and Stearokonot.
The first is the solid white adipose matter of Vanquelin, the brain wax of Gmelin. Eleencephol is a yellow red oil disagreeable odour. Cephalot is a saponifiable article. Stearokonot, also saponifiable, is hard and pulverizable.
The gray or cinereous cerebral matter, though variable in colour like the white, is in general a mixture of ash-gray and wood-brown, darker than the former, but lighter than the latter. The colour varies at different ages. It is light in early life, and deeper as life advances.
The gray cerebral matter is softer and less viscid and tenacious than white cerebral matter. It is distinctly granular, both in the external surface and when torn or broken. This appearance, however, is most distinctly recognized after induration in alcohol or acidulous liquors. In the convoluted part of the brain, where it is most abundant, it does not present the fibrous or parallel linear arrangement, and is merely an aggregated mass of numerous minute granules. It is uncertain whether it presents the fibrous arrangement in other parts of the brain. An appearance of this kind is recognized in the unciform bundle at the inner end of the fissure of Sylvius, and also in the streaked bodies and the annular protuberance. But the appearance alluded to seems to depend not on the genuine fibrous arrangement of the granules of the gray matter, but merely on the gray matter being deposited in streaks and lines between the white. Meckel nevertheless maintains that the gray matter is also fibrous.
According to the observation of Sir Everard Home and M. Bauer, the gray cerebral matter consists of minute globular atoms, smaller than those of the white matter, or varying from \( \frac{1}{32} \)th to \( \frac{1}{64} \)th of an inch in diameter. These globules appear to be united, though more loosely, by a sero-albuminous fluid of a yellower tint than that of the white matter. Home supposes this albuminous fluid to be less abundant in the gray matter.
Gray cerebral matter is well supplied with bloodvessels, which are large and numerous. It must not be imagined, however, that all the vessels which are observed to enter this substance are therefore distributed to it. These large vessels necessarily penetrate the gray matter of the convoluted surface before they reach the white matter in the centre; and though they send branches to the former, they are ultimately distributed to the latter. The gray cerebral matter, nevertheless, is generally represented to be more vascular than the white; but the circumstance now stated renders this doubtful. The statement of Sir Everard Home, that "the finest and most delicate branches of the arteries and veins are only found in the cortical, i.e., the gray substance," is contradicted by observation; for the vessels are certainly in general larger and more distinct in this than in the white matter. But if they are larger in the former, they are more numerous in the latter. On the whole, perhaps, there is little difference between the vascularity of the white and gray substance of the brain.
The chemical constitution of gray cerebral substance has not been accurately examined. The results of analysis show, nevertheless, that it contains albuminous matter to the
---
2 Du Cerveau, considéré sous le point de vue Chimique et Physiologique. Paris, 1834. 8vo. amount of about 7 per cent, with 0.70 of a peculiar red adipose matter, which is probably the cause of the peculiar colour.
These two varieties of cerebral matter are combined in various modes and proportions in the brain. In general the gray matter is found on the exterior, for instance on the convoluted surface of the brain, and on the laminated surface of the cerebellum; while the white matter is arranged in the central parts. Gray matter, nevertheless, is found in the interior, in the streaked bodies and optic thalamus, and in the moriform bodies (corpora dentata) of the cerebellum and olivary eminences.
Besides the two varieties of substances now mentioned, a third, of a deeper shade, is found in the brain. Thus, in the centre of the cerebral limbs is a quantity of cerebral matter of a dark or ink-spotted tint, which Vieq d'Azyr therefore named the black spot (focus niger) of the limbs of the brain. The nature of this black spot, which is quite uniform, is entirely unknown. It appears merely to be a modification of the gray matter.
A yellow-coloured substance has also been supposed to exist in the centrum semicirculare geminum, a narrow band between the striated body and optic thalamus. This substance is certainly firmer than the adjoining white and gray matter, and it is further peculiar in possessing a sort of tint between wax-yellow and wine-yellow. It is highly vascular. Of its other peculiarities, however, we know nothing; and we must be satisfied with regarding it as an anomalous species of animal substance, approaching to gray cerebral matter in colour, but infinitely firmer and more tenacious.
The microscopical observations made by Ehrenberg agree in some points with those made by Prochaska and Bauer; and in others they differ a little.
According to Ehrenberg, the substance of the circumference, or the convoluted part of the brain, consists of a thick, very delicate, vascular network, conveying often numerous blood-globules, and traversed by serpentine tendinous fibres. Besides the thick delicate vascular net of the first substance, Ehrenberg saw in the same, near its utmost edge and its remotest circumference, a very fine-grained soft substance, in which here and there are imbedded larger grains or nuclei. These large grains are free, and consist of granules or nucleoli, which are connected in rows by means of slender threads to the fine small threads of the substance singly. In the neighbourhood of the medullary substance, the fibrous character of the cortical matter always appears more distinctly; and in the same substance the bloodvessels are larger and less numerous.
The white or medullary matter of the brain shows more distinctly the arrangement of fibres, which proceed in the form of direct and enlarging continuations of the delicate cortical fibres, from certain eminences, that is, the linear or band-like origins of the convoluted surface, in a radiated manner, towards the brain. These are not simple cylindrical fibres; but resemble hollow strings of pearls, the component parts of which are not in contact, but are connected by a canal for a small space; or they resemble tubes or cylindrical canals dilated at intervals into minute bladders. These bladders or ampullae of the tubes were known to Leeuwenhoek, who regarded them as globules of fat, which constituted the greatest part of the brain. The connecting canals also he has obscurely indicated. These tubes, uniformly straight, are generally parallel in direction, sometimes, however, crossing each other. Four times Ehrenberg recognized ramification in such individual canals; but anastomoses he never observed. These tubes vary in diameter from \( \frac{1}{2} \)th to \( \frac{3}{4} \)th of one line.
In the neighbourhood of the base of the brain, and in the matter surrounding the ventricles, there are always seen, between these bundles of nodulated or jointed tubes, individual tubes much thicker than the rest. In these thick tubes it is often possible to recognize in their walls an external and internal boundary; or they present, besides their two external boundary lines, other two inner lines, which enable the observer to distinguish the width of the area of the internal cavity of the tubes. These nodulated linear parts of the brain are VARICOSE ARTICULATED TUBES OR CANALS.
The large cerebral tubules of the cerebral matter converge towards and pass into those parts of the base of the brain, where the peripheral nerves arise. Some of the large jointed-tube matter appears to terminate in or be connected with the cerebral cavities, in the walls of which it is well developed. Many jointed or varicose tubes pass into the spinal marrow, and thence immediately proceed to the spinal nerves.
In the spinal marrow the arrangement now described is in some respects reversed. In the brain the most vascular and delicate structure is placed at the exterior; while the least vascular, but perhaps more organized, viz., the varicose tubular structure, is placed at the interior. In the spinal chord the most vascular and delicate part lies in the centre; while it is covered externally by the coarse medullary matter.
Both substances are quite like those in the brain. From the external medullary matter, consisting of large varicose or moniliform tubes, the spinal nerves immediately proceed; and these varicose or jointed tubes, as they emerge from the investing dura mater, assume suddenly the form of nerve-tubes, becoming thicker and passing into the pure cylindrical form. These transitions are easily recognized in the posterior part of the spinal marrow.
The optic, the auditory, and the olfactory nerves are immediate continuations of, or productions from, the varicose medullary tubes of the brain. All the other nerves, excepting the sympathetic in the middle of its course, differ from the cerebral matter.
All the other nerves also consist only of cylindrical parallel-lying tubes, about \( \frac{1}{2} \)th part of a line in diameter, normally never anastomosing. These are the elementary nerve-tubes, which, united in fasciculi or bundles, again form larger bundles, which constitute the nerve-chords.
These are the chief facts ascertained by Ehrenberg regarding the minute structure of the brain and spinal chord. These have been mostly confirmed by Berres and Müller. By others, again, the accuracy of these results has been called in question. Thus the observations of Treviranus, Valentin, and Weber tend to show that all the primitive cerebral fibres or tubes are cylindrical, and that the varicose or moniliform appearance is an effect of compression, or the violence employed in subjecting them to microscopic observation. Müller, nevertheless, admits that the primitive cerebral tubes have great proneness to become varicose or beaded.
---
1 C. G. Ehrenberg in Poggendorff's Annalen der Physik und Chemie, Jahrg. 1833, Band XXVIII, § 449–65, and 1834, Band XXXIV, § 76, 80. Also Beobachtung einer bisher unbekannten ausfallenden structur des Seelenorgan bei Menschen und Thieren. Von C. G. Ehrenberg. Gelesen in der Akademie der Wissenschaften am 24 October 1833. Gedruckt im Feb. 1836. Abhandlungen; seite 665. Translated, with Additions and Notes. By David Craigie, M.D. Edin. Med. and Surg. Journal, Vol. XLVIII, p. 257, Oct. 1837.
G. Valentin über die Dicke der varicosen Fäden in dem Gehirn und dem Rückenmark des Menschen. In Müller's Archiv. 1834, § 401–410.
G. R. Treviranus Beiträge zur Aufklärung der Erscheinungen und Gesetze der Organischen Lebens Band I Heft II. 1836–8, § 24.
H. H. Weber in Schmidt's Jahrbüchern der in-und-auslandischen Medicin, Bd. XX. § 5. und Henle ebendasselbst. § 339. The only points which, amidst the discordance of the results of different microscopic observers, from Leeuwenhoek and Fontana to Ehrenberg, Berres, Treviranus, and Müller, can be regarded as established, are the following: that the convoluted portion of the brain consists of very minute granules or nucleoli arranged in rows so as to form fibres, which radiate from the periphery to the inner boundary of the convoluted portion; that near the inner boundary, and as they approach the white cerebral matter, this fibrous arrangement becomes more distinct; and that the white cerebral matter forming the walls of the ventricles and the base of the brain, is composed of tubular cylinders, mostly of large size, and having a cylindrical cavity; but whether these are varicose or not seems undetermined.
The parts named pituitary and pineal glands present several peculiarities deserving attention; but these more properly come under the head of Special than of General Anatomy.
Flesh. Muscle. (Mus.—Mus.,—Musculus,—Lacteum,—Tori.) Muscular Tissue. (Tissu Musculaire.)
The ordinary appearance of the substance named flesh or muscle is familiar; and it is unnecessary to enumerate those obvious characters which are easily recognized by the most careless observer. A portion of muscle, when carefully examined, is found to consist of several animal substances. It is traversed by arteries and veins of various size; nervous twigs are observed to pass into it; it is often covered by dense whitish membranous folds (fascia), or by serous or mucous membranes, all which shall be examined afterwards; and it is found to contain a large proportion of filamentous tissue. But it is distinguished by consisting of numerous fibres disposed parallel to each other, and which may be separated in the same manner by proper means. The appearance, arrangement, and characters of these fibres demand particular notice.
According to Prochaska, muscle in all parts of the body may be resolved, by careful dissection, into fibres of great delicacy, as minute as silk filaments, but pretty uniform in shape, general appearance, and dimensions. Their diameter appears not to exceed the \( \frac{1}{40} \)th part of an inch, whatever be their length. They seem all more or less flattened or angular, and appear to be solid diaphanous filaments. Prochaska, not doubting that these muscular threads (fila cornea) are incapable of further division, terms them primary muscular fibres.
The microscopical examination of the atomic constitution of the muscular filament, which was first attempted by Leeuwenhoek, and afterwards prosecuted by Della Torre, Fontano, Monro, and Prochaska, was resumed by Sir E. Home and M. Bauer, and subsequently by Hodgkin and Lister, Mr Skey, M. Mandl, Mr Bowman, Schwann, Henle, Remak, and Kölliker. According to the observations of M. Bauer, each muscular filament appears to consist of a series of globular or oblong spheroidal atoms, disposed in a linear direction, and connected by a transparent, elastic, jelly-like matter. (Phil. Trans. 1818, 1826.)
The primary muscular fibres are placed close and parallel to each other, and are united in every species of muscle into bundles (fasciculi, lacerti) of different but determinate size; and according as these bundles are large or small, the appearance of the muscle is coarse or delicate. In the deltoid the bundles are the largest. In the vasti, glutei, and large pectoral muscles the bundles are greatly larger than in the paes. In the muscles of the face, of the ball of the eye, of the hyoid bone, and especially in those of the perineum, these bundles are very minute, and almost incapable of being distinguished. The number of ultimate filaments which compose a bundle varies in different muscles, and probably in different animals. In a muscular fibre of moderate size in the human subject, Prochaska estimates them to vary from 100 to 200; and, in animals with larger fibres, at double, triple, or even four times that number. There is reason to conclude, from correct microscopic observation, that the largest do not exceed the eighth part of one inch, and that the smallest are not less than one-sixteenth.
According to Mr Skey, a single muscular filament has a diameter of \( \frac{1}{40} \)th part of one inch. According to Mr Bowman, who has given the diameter of the primitive fibre in many animals, both of the Vertebrated classes and the Aspidophorus tribes, the diameter varies from \( \frac{1}{12} \)th part to \( \frac{1}{5} \)th in the male, and from \( \frac{1}{12} \)th to \( \frac{1}{3} \)th part of one inch in the female of the human race. In the Mammalia and Birds, they are in general smaller. In the horse, from \( \frac{1}{10} \)th to \( \frac{1}{5} \)th; in the cow, from \( \frac{1}{10} \)th to \( \frac{1}{5} \)th; in the sheep, from \( \frac{1}{10} \)th to \( \frac{1}{5} \)th. In the owl, the diameter of these primitive filaments are from \( \frac{1}{10} \)th to \( \frac{1}{5} \)th; in the turkey, from \( \frac{1}{10} \)th to \( \frac{1}{5} \)th part of one inch.
When the muscular fibre is examined by the microscope, it is found to present transverse or cross lines, of great minuteness. These transverse streaks (striae) are conceived to indicate circular annular markings going all round the fibre. They are placed closely together, but varying much in thickness and in number; a portion of the length of the fibre, equal to its diameter, containing, according to Mr Skey, from sixteen to twenty-five streaks.
These transverse lines are not seen with equal distinctness in all the muscular fibres of the voluntary muscles. When distinct, they present themselves in the form of rings, pretty well defined, the extremities of which may be distinctly traced, encircling the fibre, equidistant from each other, uniform in diameter, and apparently raised from the surface into ridges, having depressions between them. Mr Skey infers, as in certain lights light-coloured lines are seen, and dark intervening lines, that the light lines are the elevated striae, and the dark-coloured lines are the intermediate depressions.
These alternate light and dark-coloured transverse lines are characteristic of voluntary muscles in all parts of the body, and in all animals. They are not observed in the muscles of organic life, or those of the involuntary organs, the heart excepted; for instance, the muscular fibres of the stomach, of the intestinal canal, and the bladder.
The muscles which present these cross-lines are sometimes named Striped muscles; and as the aspect remotely imitates a string of beads, they are occasionally called Beaded muscles. In consequence of the stripes being found solely in the voluntary muscles, the latter are often called Striped and Beaded muscles.
The nature of these transverse lines and markings is not perfectly known. Prochaska appears to have believed that they were produced by minute flexuosities of fibrils, and connected in some manner with the filamentous tissues. Fontana believed that they were caused by small diaphragms or partitions of the primary filaments. Mr Skey remarks, that the striae are invariably large as the fibre is small, while the broad fibres exceeding the average diameter of \( \frac{1}{10} \)th part of one inch, exhibit the most delicate and minute pen-cilling possible. He infers that these striae are ridges or elevations on the longitudinal fibre, leaving between them depressions considerably smaller than the globules of the blood; that each fibre is divisible into fibrilla, which are composed of many ultimate filaments, and which are arranged in
---
1 On the Elementary Structure of Muscular Fibre of Animal and Organic Life. By F. C. Skey, F.R.S. Phil. Trans., Lond. 1837. Vol. xxi. p. 371. On the Minute Structure and Movement of Voluntary Muscle. By W. Bowman. Ibid. 1840, Art. xxi. p. 457. parallel lines round the axis of the fibre; that the muscular filaments have a diameter of about the third part of a globule of the blood; that they are tubular, and contain a soluble glutinous substance; and that this structure belongs to all the external muscles, and all the internal muscles connected to any form of tendinous matter.
According to Mr Bowman, several of these views of Mr Skey are not susceptible of strict proof. Mr Bowman represents the primitive fasciculi of the fibre of voluntary muscles to consist of elongated polygonal masses of primitive component particles, or what he calls Sarkous elements, arranged and united together both by their ends and by their sides, so as to constitute in these directions respectively fibrillar and disks, both of which exist together in the perfect unmutilated muscular filament, and either of which may, in certain cases, be detached separately. According to the same observer, the dark longitudinal striae are shadows between fibrilla; the dark transverse streaks are shadows between disks. The primitive fasciculus consists of primitive component segments or particles, arranged so as to form in one sense fibrilla, in another disks; and which of these two present themselves to the observer, depends upon the amount of adhesion. Generally, in a recent fasciculus, there are transverse striae or stripes, showing the division into disks, and longitudinal lines marking the division into fibrilla. These striae, in short, are the edges or focal sections of plates or disks arranged vertically to the course of the fasciculi, and each of which is composed of a single segment from each fibrilla.
The fasciculi are not tubular and hollow, but consist of a true bundle of fibrilla. That this is the fact, Mr Bowman argues, is proved by making a transverse section, which presents no appearance of any cavity.
By cutting a muscle across, these bundles are observed to differ, not only in size, but in shape. Some are oblong and rhomboidal, others present a triangular or quadrangular section, and in some even the irregular pentagon or polygon may be recognized.
According to the observations of Kölliker, the form most usual is that of the hexagon, not quite regular; and when two sides run into one, it assumes the shape of the pentagon. Bowman merely says, that they are in all animals polygonal, though in some instances they make a near approach to the cylindrical form. This is easily understood. If the angles be rounded, the filament that might be polygonal or hexagonal becomes cylindrical.
These bundles or fasciculi are united by filamentous tissue of great delicacy. Each filament or fibril is inclosed in a sheath of peculiar matter, described by Schwann, and afterwards by Bowman, under the name of Sarkolemma, or Flesh Coat. This structure is entirely different, according to the last author, from filamentous tissue, either penetrating or generally investing. It may be discovered in unbroken fasciculi, in the form of a straight linear margin, quite unconnected with and independent of the striae. The sarcolema is tougher and firmer than the muscular filament.
The fibrils and fibres thus inclosed in Sarkolemma are united into Fasciculi, which are inclosed by filamentous tissue, and are penetrated by arteries, veins, and nerves. The whole are surrounded by filamentous tissue, which often contains fat; in many instances covered by fascia; in all attached by tendons.
This fascicular arrangement appears to be confined to the muscles of voluntary motion. It is not very distinct in the heart or diaphragm; and in the urinary bladder and intestinal canal it is not recognised. Nor is the parallel arrangement of the ultimate filaments always strictly observed in the involuntary muscles. The component fibres of this order of muscles are often observed to change direction, and unite at angles with each other. This fact, which was observed by Leeuwenhoeck, has been verified by Prochaskin.
The colour of muscle varies. In man and the mammiferous animals, at least adult, it is more or less red; in many birds and fishes it is known to be whitish; in young animals it is grayish or cream-coloured; and the slender fibres which form the middle coat of the intestines in all animals are almost colourless. The colour of the muscles of voluntary motion in man is red or fawn; but repeated washing or maceration in alcohol or alkaline fluids renders them much paler.
The examination of the physical properties of muscle has occupied the industry of Muschenbroek, Croone, Browne Langrish, Wintringham, and others of the iatro-mathematical school. I cannot perceive that minute knowledge of these properties is of much moment to the elucidation either of its sound or its morbid states. Amidst the variable results obtained in such an inquiry, the only certain point is, that muscular fibre has less tenacity and mutual aggregation than most other tissues. It sustains much less weight and force of tension without giving way.
Chemical analysis has not yet furnished any satisfactory results on the nature of muscular tissue; but the general results of the numerous experiments already instituted show that muscle contains fibrin, albumen, gelatine, extractive matter (osmazome), and saline substances. It is difficult to say how far the gelatine is to be regarded as proper to muscle, or derived from the filamentous tissue in which it certainly exists. The saline matters are common to muscle with most other organic substances. There is reason to believe that fibrin in considerable quantity and albumen and osmazome in smaller proportion, are the proper proximate principles of muscle. Though the various proportions of these principles have been stated in numbers by chemists, it is impossible in the present condition of animal chemistry to place any reliance on them. It is also to be remembered that the relative proportion of the proximate principles varies at different periods of life. In early life the muscular fibre contains a large proportion of gelatine, and very little albumen, fibrin, or osmazome. In adult age, however, the gelatine is very scanty, and the fibrin is abundant. The albumen and gelatine found in muscle seem to be derived chiefly from the filamentous tissue and the aponeurotic intersections.
During life the muscular fibre possesses the property of shortening itself or contracting under certain conditions. These may be referred to the following heads: 1st, The will in the voluntary muscles; 2d, proper fluids in the involuntary muscles, as the blood to the heart, articles of food or drink in the stomach, chyme in the small intestine, excrement in the large intestine, urine in the bladder, &c.; 3d, mechanical irritants in all muscles; 4th, chemical irritants; and, 5th, morbid products generated in the course of disease.
This property of contracting has received various names: contractility, vis contractilis of L. Bellini; irritability of Glisson; vis vitalis of De Gorter and Gaubius; excitability, mobility, vis insita, vis propria of Haller; and the organic contractility of Bichat. It is peculiar to muscular fibre, and is found in no other living tissue.
The inquiry into the properties peculiar to muscles, and the influence of the brain and nerves over muscular contraction, forms an interesting subject of investigation, on which many facts have been communicated since the time of Haller and Whytt, and within the last forty years by Nysten, Le Gallois, Wilson Philip, Bell, Magendie, Flourens, Fodera, Rolando, and Longuet. But it is too extensive to be considered in this place; and, for information The muscles have been divided, according to the manner in which the phenomena of contraction take place, into, 1st, muscles obedient to the will, or voluntary; 2d, muscles not under the influence of the will, or involuntary; and, 3d, muscles of a mixed character, the motions of which are neither entirely dependent nor independent on the will.
The first order comprehends all the muscles of the skeleton; the second includes the hollow muscles, as the heart, stomach, and intestinal canal; and in the third are contained such muscular organs as the diaphragm, intercostal muscles, bladder, rectum, &c.
The muscles have also been distinguished, according to their mechanical shapes, into long muscles (musculi longi, vel teretes), broad muscles (musculi lati), and irregular muscles, or those of mixed form. The long muscles are found chiefly in the extremities; the broad muscles in the trunk; and those of irregular shape either in the trunk, or passing from this to the extremities. From the direction of their fibres, several of them are distinguished into penniform and semipenniform.
**Sinew, Tendon. (Tendo.)**
Sinew or tendon was united by Bichat with ligament, fascia, aponeurosis, and periosteum, under the general name of fibrous system; and the substance of this arrangement has been adopted by Gordon, Meckel, and Beclard. From personal observation, however, I am inclined to regard tendon as essentially distinct, at least in the present state of knowledge, from these substances. Examined anatomically, it does not bear a very close resemblance to any of them; and in its known chemical properties it is considerably different.
The appearance of this substance must be familiar. Almost cylindrical in shape, but flattened at the muscular end, and tapering where inserted, a tendon consists of numerous white lines as minute as hairs, of satin-like glistening appearance, placed parallel and close to each other. A tendon is easily divided, and torn into longitudinal or parallel portions; and by the forceps very minute fibres may be detached and removed with ease, its whole length. These facts show the great tenacity of this tissue, and the regular parallelism with which the component fibres are united. The last circumstance distinguishes them completely from ligaments and periosteum, in which the fibres cross in all directions, and in consequence of which these tissues cannot be so easily split or separated. These fibres are united by filamentous tissue.
Tendon is softened and more easily separable by maceration in water or alkaline fluids; it is crisped by acid fluids, and rendered translucent by immersion in oil of turpentine. It has not been injected, but it is presumed to have blood-vessels and absorbents. No nerves have been traced into it.
Tendon when boiled becomes soft and large, assumes the appearance of a transparent gelatinous substance, and finally, if the boiling be continued, is dissolved and converted into gelatine. This fact, which is well known to cooks, who prepare jellies from tendinous parts of young animals, shows that tendon consists principally of gelatine, disposed in an organized form.
A species of flattened tendons, to which the name of aponeurosis has been given, may justly be united with this tissue. The best examples are in the aponeurotic or tendinous expansion of the external oblique muscle of the abdomen, the aponeurotic part of the occipito-frontal muscle of the head, and the upper or broad end of the tendo Achillis. The anatomical structure and the chemical properties of each of these varieties of animal substance are quite similar, and somewhat different from that which has been termed fascia.
**White Fibrous System. Ligament. (Διαγόνης, ο Διαγόνου.)**
**Periosteum.—Dura Mater.—Fascia.**
Against the formation of this order of tissues fewer objections can be urged, though ligament and periosteum undoubtedly furnish its most perfect examples; and it may be doubted whether fascia ought to be referred to it, or arranged with tendon and aponeurosis. The dura mater, the tunica albuginea, and the fibro-synovial sheaths, are to be regarded as compound membranes.
Ligament and periosteum are easily shown to consist of strong whitish or gray fibres, as minute as threads or hairs, interwoven together in various directions, and thus forming an animal substance which is not to be split or torn asunder as tendon; but when ruptured by extreme force presents an irregular ragged surface or margin. Maceration in water or alkaline fluids separates the component fibres, and shows their irregular disposition more distinctly. They are crisped by diffusion of boiling water, or immersion in acids; and they become translucent by immersion in oil of turpentine.
The properties of this tissue are chiefly physical. Those which are vital are referable to its organization and nutrition. That it is powerfully resisting, and is one of the toughest and strongest tissues in the animal body, is evinced not only by the numerous experiments recorded in the writings of the iatro-mathematical physiologists, but by the barbarous mode of punishment by rending the limbs asunder by horses. It is supposed to possess the exhaling ends of arteries and colourless veins. No nerves have been recognised; and Bichat expresses his ignorance of absorbents being traced into it.
Ligament when boiled yields a small portion of gelatine, but obstinately resists the action of boiling water, and retains both its shape and tenacity or cohesion. The crispation which it undergoes in boiling water, alcohol, and diluted acids, seems to indicate that albuminous matter forms its chief chemical principle.
As to their mechanical shape, the ligaments are divided by Bichat into two sorts; those in regular and those in irregular bundles. The former comprehends all the distinct clusters of ligamentous structure, which, sometimes in a cylindrical, sometimes in a flattened shape, connect the articulating ends of bones, and form the lateral ligaments of the various articulations. The latter consists of those loose parcels of ligamentous fibres which are found in various regions of the skeleton, not in regular cylindrical or longitudinal bands, but irregularly connecting bones not admitting of articular motion; for instance, at the symphysis pubis and the sacro-iliac junction. The division of Beclard into articular, non-articular, and mixed, is more comprehensive and more natural. The first are those which connect the articular extremities of different bones. The second are those which, attached to different parts of the same bone, convert notches into foramina, as in the orbital arch and the supra-scapular hollow, or close openings, and give attachment to muscles, as the obturator ligament.
The last are those which, like the sacro-ischiatic or the interosseous ligaments of the forearm and leg, connect bones susceptible of little or no motion, and especially periosteum, give attachment to muscles. The two latter species of ligaments approach closely in their characters, physical and anatomical, to periosteum, and are probably to be regarded as modifications of this membrane.
The articular or perfect ligaments are naturally divisible into two subgenera,—the capsular and the funicular.
The capsular ligaments, or the fibrous capsules (Bichat), consist of cylindrical ligamentous sheaths attached all round to the ends of the articulating bones, and intimately interwoven with the periosteal tissue. Consisting essentially of fibro-albuminous matter strongly compacted, they are surrounded by cellular tissue, or rather cellulose-adipose tissue, and are lined internally by synovial membrane. Though the most perfect examples of the capsular form of ligament are presented in the scapulo-humeral and coxo-femoral articulations, less complete ones, nevertheless, are seen in the other joints. In those of the knee and elbow, an arrangement of this kind may be demonstrated; and minute capsules may be shown to connect the oblique articular surfaces of the vertebrae with each other.
The funicular ligaments, which consist of round chords or flat bands, are employed in connecting the articular ends of bones either without or within the cavity of the joint. Of those of the former description, the best examples are seen in the elbow and knee joints, and in the wrist and ankle, where they are termed lateral ligaments (lateralia, accessoria). Of the latter instances are the round ligaments (ligamenta teretia) of the shoulder and hip joints, and the crucial ligaments of the knee-joint. These receive an investment of synovial membrane.
Of the white fibrous tissues, one of the most important is that denominated fascia. Consisting in intimate structure of long fibrous threads placed in parallel juxtaposition, sometimes obliquely interwoven and closely connected by filamentous tissue, it forms a whitish membranous web, variable in breadth, of some thickness and great strength. Fascia is perhaps, not excepting the skin, the most extensively distributed texture of membranous form in the animal body. It not only covers, if not the whole, at least by far the greatest part of the muscles of the trunk and each limb, but it sends round each muscle productions by which it is invested and supported, and even penetrates by minute slips into the substance of individual muscles. Of several of the large muscles it connects the component parts, as is seen in the recti abdominis; to many it affords points of origin or insertion; and to all it furnishes more or less investment and support. Most of the tendons, especially the flexor and extensor tendons, are inclosed by it; and their synovial sheaths derive from it their exterior covering. At the extremities of the bones it is connected with the ligaments and periosteum, with which it is closely interwoven; and it forms a general investment to the articular apparatus.
Though fascia may thus be viewed as one membranous web consisting of many parts all directly connected with each other, it is the practice of anatomists to distinguish its divisions according to the region which they occupy. Thus, in the fore-part of the neck and chest is found a fascia, the relations and uses of which have been well described by Mr Allan Burns. In the cervical region we find a firm fascia descending from the occipital bone along the vertebrae, covering and connecting the muscles of each side till it reaches the loins, where, in the form of a thick strong membrane, it forms the lumbar fascia (fascia lumborum). It may further be traced over and between the glutei muscles, connected afterwards with the broad femoral fascia (fascia lata), and thence over the knee and leg to the foot. Much in the same manner a membranous web, thinner and more delicate, but of the same structure, may be traced from the chest along the upper extremity, till at the wrist it is identified with the annular ligament, and in the hand with the palmar fascia. In all these situations the general fascial envelope sends slips or productions (fasciae intermusculares) between the muscles, and into their substance.
Yellow Fibrous System. Elastic Ligaments of John Hunter. (Ligamenta Flava.—Ligamentum Nuchae.—Tissu Fibreux Jaune, Beclard.)
The yellow ligaments (ligamenta flava) which connect Elastic the spinous processes of the vertebrae to each other differ considerably from the articular ligaments and the periosteum, and suggested to Beclard the necessity of establishing a particular order of fibrous tissues, to which he applies the denomination of yellow or tawny fibrous system. Under this he includes also the proper membrane of the arteries; that of the veins and of the lymphatic vessels; the membranes which form excretory ducts; that of the air-passages; the fibrous covering of the cavernous body of the urethra, and perhaps that of the spleen. The actions and occasional distensions of which these parts are the seat require, it is said, a tissue, the resistance and elasticity of which may at once counteract any extraordinary effort, and cause them to resume their original state, when the distending cause ceases to operate. In the lower animals this purpose is more conspicuous than in the human subject. The posterior cervical ligament (ligamentum nuchae, Arab.; cervix, Lat.) in the camel, giraffe, deer, and ox, counteracts the tendency to inclination of the head; and a similar membrane strengthens the abdominal parietes, and resists the weight and distending power of the viscera. In the feline tribe an elastic ligament inserted into the ungual phalanges retains them extended so long as the muscles do not alter their direction. The shells of the bivalve molluscous animals, as oysters, mussels, &c., are opened by a similar fibrous tissue as soon as the muscles which close them are relaxed.
The disposition of the component fibres is the same in the elasticas in the common white fibrous system. Their colour, which is yellow or tawny, is generally more distinct in the dead subject. They are said to be less tenacious, but more elastic, than those of any other tissue. In respect to chemical composition, they appear to contain a considerable quantity of fibrin in a peculiar condition, combined with some albumen and a little gelatine. Their other properties are not very conspicuous.
Bone. (Osseus.—Osso.—Tissu Osseux.—Die Knochen.)
Bone, which is the hardest and most durable of the animal solids, may be defined to be an organized substance, consisting of a combination of animal and calcareous matter, and constituting by its solidity the chief support of the soft parts generally.
In the vertebrated animals it is moulded into pieces of definite shape and size, which are connected either by ligaments, cartilage, or fibro-cartilage, and which constitute the skeleton of the animal. In the mammalia and birds these pieces appear in their most perfect characters, as to solidity, mechanical shape, and numerical extent. In the human subject, though in these respects they partake of the characters common to the bones of the mammalia, in several senses these characters are more conspicuous than in the lower animals. The bones of the human skeleton are distinguished according to the varieties of mechanical figure, into long and cylindrical bones (ossa longa sive cylindrica), flat bones (ossa lata sive plana), and short or irregular bones (ossa brevia sive mixta).
The long bones are confined to the extremities, where they are subservient to the locomotive apparatus, by acting alternately as points of support and as levers movable by the muscles in different directions. Placed in the centre, they are surrounded almost entirely by muscles; and are observed to diminish in length, but increase in number, the farther they recede from their attachment to the trunk. From this inverse arrangement it results that near the trunk the members are distinguished for extent, and remote from it for variety and multiplicity of motion.
The long bones agree in presenting cylindrical or prismatic shafts (diaphyses) terminated by large, bulky, and extensive extremities (epiphyses). The former are generally small and slender compared with the latter and with the size of the limb, and thus afford room for the bellies of muscles attached to them. The large size of the latter is well suited for the extent of the articular surfaces; and being covered by slender tendons and the taper extremities of muscles, they do not in general add to the bulk of the member.
The shafts of the long bones are in general marked by longitudinal rough lines, to which muscles or fasciae are attached, and between which are found plane or hollow surfaces for lodging the bellies of the muscles. These lines are rarely straight; and the slight obliquity which they observe gives the bone the appearance of being twisted. This is well seen in the humerus and tibia.
The extremities of the long bones are marked in general by eminences and hollows, or processes (apophyses) and depressions (forae; fossae). These inequalities, if tipped with cartilage and synovial membrane, are for the purpose of articulation with other bones. When they are simply formed of bone, they are for the attachment either of ligaments or tendons.
The shafts of the long bones consist chiefly of dense compact bone, containing in the adult a longitudinal cavity, which is easily exposed by a longitudinal section of the bone. This cavity is not cylindrical, but tapers considerably at each end; nor is it in all instances equally complete. Largest and most capacious about the middle, where it is bounded by the solid, compact, bony walls of the diaphysis, as the latter diminish in density they increase in bulk by the formation of numerous minute intersecting columns of bone, which progressively increasing in number towards the end of the shaft, contract the cavity, until at length it is obliterated in the lattice-work and cells (canaliculi) formed by their mutual intersection. This cavity is the medullary canal. It is seen in its most perfect form in the humerus and femur, in the tibia and fibula, and in the radius and ulna. In the phalanges it can scarcely be said to exist. The two forms of bony structure demonstrated in such a section are distinguished as the dense or compact, and the loose, reticular, or cancellated.
The medullary cavity is lined by a vascular filamentous membrane, with numerous cells, containing the variety of animal fat denominated marrow. The effect of this arrangement is to render the bone lighter than if perfectly solid, without any diminution of strength. This cavity is wanting in the original formation of the bone; and it begins to be formed when the matter of the diaphyses becomes dense and compact. It is again obliterated in consequence of fracture or other injuries, succeeded by adhesive or depository inflammation, when it is filled by gelatinous animal matter; and it is once more excavated as the walls of the diaphysis acquire solidity.
The flat bones are in general less connected with the locomotive apparatus than with the protecting part of the skeleton. By mechanical configuration they serve to contain various organs essential to the economy; and when they admit of motion, this is rarely locomotive, but connected with the purposes of the contained organs. The bones of the cranium and pelvis furnish the best examples of bones destined solely to protect, and as locomotive agents affording only points of support. The ribs, again, which are to be viewed as flat bones, not only form the protecting walls of the chest, and furnish support to the muscles of the upper extremities, but further undergo a slight motion, by means of which the dimensions of the chest are alternately enlarged and diminished. The vertebrae combine the characters of flat bones and irregular bones, approaching by their spinal plates to the former class, and by their bodies to the latter.
In number the flat bones vary according to the purpose to which they are applied, and the nature of the cavities which they form. In the cranium and pelvis their numerical extent appears to bear relation chiefly to the facility of ossification,—a process which advances with equal rapidity in each individual piece. In the chest, again, this property is regulated by the kind of motion which the ribs are destined to undergo. The vital organs of circulation and respiration would no doubt have been more securely protected had they been inclosed, like the brain, in a continuous and complete osseous case; but by this arrangement the motions of inspiration and expiration must have been very limited.
The flat bones agree in being convex and concave in opposite directions; in possessing two surfaces, an external and an internal, and a circumference; and in consisting of an external and internal table or thin plate of bone, with loose cancellated structure interposed. This arrangement is most conspicuous in those of the cranium, in which the cancellated structure is distinguished by the name of diploe. It is nevertheless equally distinct in the ribs, the scapula, and the pelvic bones. In some instances in the latter, the diploe is obliterated, and the two tables approach each other so closely, that they form one bone; and occasionally this is destroyed, and the bone appears perforated. These effects are the result of long-continued muscular action.
The cancellated structure of the flat bones is lined by a vascular filamentous membrane, containing a small proportion of marrow, less oleaginous than that of the long bones, and entirely resembling those of the cancellated structure of their epiphyses.
The short bones are situate in parts requiring the combination of mobility and solidity; for example, the vertebral column, the carpus and metacarpus, the tarsus and metatarsus. Considerable extent of surface, numerous articular and ligamentous connections, with few muscular or tendinous insertions, are their leading external characters.
They consist of a single thin external plate of bone, inclosing a large proportion of cancellated structure, lined by vascular filamentous tissue, containing semifluid marrow, without much oil. While this arrangement combines very small specific gravity with sufficient firmness and solidity, it renders them more liable to arrangements of organization than other parts of the osseous system.
Though the bones are thus distinguished according to general characters, it is often impossible to apply them accurately. The same bone may unite the characters of long and short bone, or flat and short bone, or long and General flat bone. All the long bones indeed are in their epiphy- ses similar to the short bones.
In external figure the bones present certain eminences or processes (apophyses), and pits or cavities (forae; fossae). The eminences are either articular or non-articular. The former, which are covered with cartilage or fibro-cartilage, belong to the subject of the connections of bones. The latter may be referred to three heads: 1st, eminences of insertion for ligaments, tendons, or aponeuroses; 2d, emi- nences of reflection for the transit of tendons round a pulley; and, 3d, eminences of impression, or those which correspond to various soft parts in contact with the bones.
The eminences of insertion appear in various shapes, and are distinguished into tuberosities and tubercles (tubera), spines (spinae) or spinous processes, styloid pro- cesses (styli), crests (crista), and lines (lineae), which are generally rough and elevated. These impressions are al- ways more conspicuous in the male than in the female, in the old than in the young, in the robust and muscular than in the delicate and feeble, and in carnivorous than in herbivorous animals. In some instances, as in the case of the ischial tuberosity, the great trochanter and anterior tu- berosity of the humerus, the eminences present individual facettes for the attachment of each tendon or muscle.
Of the eminences of reflection, the best examples are in the unciform process of the pterygoid process of the sphenoid bone, and the lower extremity of the fibula.
The depressions are either articular or non-articular. The latter consist of cavities of insertion, reception, transmission and motion, impression and nutrition.
The first, which give attachment to ligaments, tendons, or aponeuroses, are useful in augmenting the extent without increasing the size of bones. The pterygoid ca- vities, the digastric fossa, and that at the base of the great trochanter, afford examples of these cavities.
Of the cavities of reception, examples are seen in the cerebral and cerebellar fossae, and in the grooves for arteries or nerves; for instance, that at the lower margin of the ribs, and the various openings in the cranium for the transit of vessels and nerves.
Cavities of motion are those over which tendons play in the contraction of muscles; the bicipital groove, the hollow between the ischial spine and tuberosity, and that in the fibula for the peronaei, are examples.
The cavities of impression alternate with the eminences, and are to be regarded as in general the cause of these emi- nences.
The cavities of nutrition are those minute orifices through which vessels convey to the substance of the bone, or the medullary membrane, the materials of its nutrition. Each long bone has one considerable hole of this kind in its shaft, and numerous minute ones in its extremities. The former is the orifice of a canal to the medullary cavity. The latter are supposed to belong chiefly to the cancellat- ed structure.
2. Several attempts have at different times been made to ascertain the atomic constitution of bone, but without much success. Malpighi, though he corrected the extra- vagant fiction of Gagliardi regarding the osseous plates and nails, fancied bones to be composed of filaments, which Leeuwenhoek represented as minute tubes (tu- buli). By Clopton Havers, again, the ultimate parti- cles of bones were imagined to be fibres aggregated into General plates (lamines) placed on each other, and traversed by longitudinal and transverse pores (pori). This view was adopted by Courtial, Winslow, Palfyn, Monro, and Reichel, who was at some pains to demonstrate this ar- rangement of plates and minute tubes by microscopical observation. These notions were first questioned by Scarpa, who, in 1799, undertook to show by examinations of bone deprived of its earth by acid, and long macerated in pure water, that it consists, both externally and inter- nally, of reticular or cellular structure. So far as I un- derstand what idea this eminent anatomist attaches to the terms reticular and cellular, I doubt whether this opinion is better founded than any of the previous ones. After repeating his experiment of immersing in oil of turpentine bone macerated in acid, I cannot perceive the reti- cular arrangement which Scarpa describes. Recently bone has been submitted to microscopic examination by Mr Howship, who revives the opinion of the existence of mi- nute longitudinal canals, as taught by Leeuwenhoek, Havers, and Reichel, but with Scarpa maintains the ulti- mate texture not to be laminated, but reticulated. Lastly, the existence of fibres and plates, which is admitted by Blumenbach, Bichat, and Meckel, apparently on insuffi- cient grounds, is to be viewed as an appearance produced by the physical, and perhaps the chemical qualities of the proper animal-organic matter of which bone consists. Though it does not demonstrate, it depends on, the inti- mate structure of this body.
The minute structure or atomic constitution of bone is probably the same in all the pieces of the skeleton, and is varied only in mechanical arrangement. When a cylin- drical bone is broken, and its surfaces are examined with a good magnifying glass, or when minute splinters are in- spected in a powerful microscope, it appears to be a uni- form substance without fibres, plates, or cells, penetrated everywhere by minute blood-vessels. Its fracture is un- even, passing to splintery. In the recent state its colour is bluish-white; but in advanced age the blue tinge dis- appears. Delicate injection, or feeding an animal with madder, shows the vascularity of this substance.
To have a clearer and more accurate idea of the minute structure of bone, it is requisite to break transversely a long bone, and examine its fractured surface by a good glass, or to examine in the same manner the transverse fracture of a long bone which has been burnt white in a charcoal fire. The broken surface presents a multitude of minute holes, generally round or oval, which are larger towards the medullary cavity, but become exceedingly minute towards the outer surface of the bone. Of these minute holes no part of the bone, however compact in ap- pearance, is destitute; and the only difference is, that they are more minute, and more regularly circular towards the outer than towards the medullary surface. These circular holes are transverse sections of the tubuli of Leeuwenhoek, the longitudinal pores of Havers (Osteo- gia, p. 43 and 46), the pores and tubuli of Reichel, and the longitudinal canals of Howship. They communicate with each other by means of their great multiplicity and slight obliquity and tortuosity. They contain not blood-vessels exclusively, but divisions of the vascular filamentous tis- sue, which secretes the marrow. They are seen very dis- tinctly in bones which have been burnt. After many care-
---
1 The principal authors on the structure of bone are, Dominici Gagliardi Anatomia Ossium, novae inventionis illustrata. Roma, 1689. Malpighi, De Osium Structura: Op. Post. Clopton Havers, Osteologia Nova. London, 1691. Delassein, Memoire sur l'Organisation des Os: Mem. de l'Academie, 1751. G. C. Reichel, De Osium Ortu atque Structura. Lips, 1760. Ext. in Sandifort Thesaurus, vol. ii. p. 171. Anteall Scarpa de Peritiori Ossium Structura Comment. Lips, 1799. Republished in De Anatomia et Pathologia Ossium Commentariis, Auctore A. Scarpa. Ticini, 1827. Papers by Mr Howship in the 6th and 7th volumes of the Medico-Chirurgical Transactions. ful examinations, I have never been able to observe holes in longitudinal fractures of bones; and I therefore infer that there are no transverse pores.
These capillary pores are seen in the flat bones of the skull. I find them in the compact matter of the outer and inner tables of the occipital bone when well burnt, in which they seem to pass gradually from the lattice-work of the diploe to the distinct pores of the tables. I doubt, however, whether these pores can be said, as in the long bones, to indicate canals. They seem rather to belong to a very delicate cancellated structure. The pores are most numerous and distinct in the bones of young subjects.
Though these circular pores are most distinct in calcined bones, and might therefore be thought to be the result of the burning, yet that they are not, I infer from the circumstance that they are seen by a good glass in the transverse fracture of splinters of the femur and other large bones.
If a portion of bone be immersed in sulphuric, nitric, muriatic, or acetic acid, properly diluted, it becomes soft and pliable, and when dried, is found to be lighter than before; yet it is impossible to discover that any particle of its substance has been removed, or that its mechanical shape and appearance are changed.
If a portion of bone be placed in a charcoal fire, and the heat be gradually raised to whiteness, it burns first with flame, and at length becomes quite red. If then it be removed carefully and slowly cooled, it appears as white as chalk, is found to be very brittle, and to have lost something of its weight. Yet neither in this case does any part of its substance appear to be removed, nor is its mechanical figure or appearance altered.
Chemical examination, however, informs us that in the first case a portion of earthy matter (phosphate of lime) is removed by the agency of the acid, and held suspended in the fluid, while the plant but otherwise identical piece of bone consists chiefly, if not entirely, of animal matter; and that, in the second case, this animal matter is removed by destructive decomposition, while the earthy matter is left little changed by the action of fire. Every particle of bone, therefore, however minute, consists of animal or organic, and earthy or inorganic matter, intimately united; and it is impossible to touch, with the point of the smallest needle, any part of bone which is not thus constituted.
A piece of bone consists not of cartilaginous fibres varnished over, as Herissant imagined, with earthy matter, but of a substance in which every atom consists of animal and earthy matter intimately combined.
There is therefore no ground for dividing osseous tissue into compact and spongy, as the old anatomists did; for though the middle parts of long bones are denser and heavier than their ends, or the bodies of the vertebrae, the difference consists not in chemical composition, but in mechanical arrangement. On dividing the head of a long bone, the lattice-work, or cancelli, as they are named, are formed by many minute threads of bone, crossing and interlacing with each other. But each thread is equally dense, and consists of the same quantity of animal and earthy matter, as the most solid part of the centre of the same bone. These threads, however, instead of being disposed compactly so as to take a small space, are so arranged that they occupy a large one, and present considerable bulk.
Though bone has been submitted to analysis by many eminent chemists, the results hitherto obtained cannot be said to be quite satisfactory. The most recent is that of Berzelius, who, in 100 parts of bone from the thigh of an adult, gives the following proportions: of gelatine 32-17, blood-vessels 1-13, phosphate of lime 51-04, carbonate of lime 11-30, fluate of lime 2-00, phosphate of magnesia General 1-16, hydrochlorate of soda and water 1-20.
These results by no means agree with those obtained by Fourcroy and Vanquelin, who found neither fluoric acid nor phosphate of magnesia, but discovered oxides of iron and manganese, silica, and alumina, in bone. Sulphate of lime, which was found in the experiments of Hatchett, was shown by Berzelius to be formed during calcination. It is, however, obvious that a little more than a third part of bone consists of animal matter, which appears to be either gelatine, or a modification of that principle; and that the remainder, nearly equal to two thirds, consists of earthy matter, which is chiefly phosphoric acid combined with lime. The carbonic acid said to be united with lime may result from the decomposition of the animal matter. The other saline substances are not peculiar to bone, but, being common to it and the other animal tissues, and even the fluids, may be supposed to be derived from the blood left in the bone at the moment of death.
The animal matter of bones was at one time presumed to be cartilage; but this appears to be an assumption, derived from the superficial resemblance which it bears to this substance. It does not appear to be mere gelatine; for though this principle is obtained from bone, and bones are economically used in manufacturing glue, they do not furnish the same proportion of jelly as tendon, nor are they so useful in making soups, as was once paradoxically maintained by some chemists. It is probable that the gelatine is under a peculiar modification, or combined with some principle which is not well understood. The sulphur formed during calcination seems to show that this animal matter contains albumen. There is no fat in bones; and in the experiments in which this substance was found, it is evident that marrow had been mingled with the bones employed.
Though bones were arranged by the ancients among the Organizableless organic substances, they receive a considerable proportion of this fluid, and injection shows them to be highly vascular. In early life especially these vessels are numerous; and even in the grown adult, when death takes place by strangulation or by drowning, the bones are found to be naturally well injected. In old age the vessels are less numerous, but they are larger. From the capillary vessels distributed through their substance, bones derive the pale blue or light pink colour by which the healthy bone is characterized. When this tint becomes intense, it indicates inflammation or some morbid state of the vessels of the bone. When it is lost, and the bone assumes a white or yellow colour, the part so changed is dead.
Anatomists distinguish three orders of vessels which enter the substance of bones; the first, those which penetrate the bodies of long bones to the medullary cavity (arteriae nutritiae, arteriae medullares); the second, those which go to the cellular structure of the bone; and the third, those which go to the compact or dense matter of the bone. The view is only partially correct. The large vessels termed nutritious certainly proceed chiefly to the cavity of the bone, and are distributed in the medullary membrane. These, however, are not the only vessels which proceed to this part of the bone. First, I have often traced several large vessels, entering not by the middle, but the ends of the long bones, into the loose cancellated texture, and actually distributed on the medulla in this part of the bone. In dried bones also the canals of these vessels may be demonstrated, extending from the surface to the body of the bone. Secondly, the nutritious vessels are not constant; and when they are wanting, those of the ends of the bone, or of the cancelli, are much larger and more numerous than in ordinary circumstances. General The communication between these and the branches of the nutritious vessels, which is admitted by Bichat, may be easily demonstrated. The third order of vessels are those which may be termed periosteal, in so far as they consist of an infinite number of minute capillaries, some red, some colourless, proceeding from the periosteum to the bone, and contributing to maintain the connection between the two. The short bones and the flat bones, which are destitute of nutritious arteries, receive blood from the two latter orders, but principally from the periosteal vessels. In the skull these vessels are often highly injected in apoplectic subjects, and in persons killed by drowning or strangulation.
The veins of bones are peculiar in their arrangement. The nutritious artery is accompanied by a social vein; the articular and periosteal vessels are said to be destitute of corresponding venous vessels. According to Dupuytren, however, minute venous capillaries arise from the substance of the osseous tissue, precisely as in other tissues, and, uniting in the same manner, form twigs, branches, and trunks, which finally terminate in the neighbouring veins. Lymphatics are not found in bones, nor have nerves been traced into their substance.
Marrow. To complete the anatomical history of bone, it is requisite to examine shortly the marrow. The interior of the long bones contains a quantity of fat, oleaginous matter, which has been long known under the name of marrow (μαρούλη, medulla); and a similar substance, though in smaller quantity, is found in the loose cancellated tissue of the flat and short bones. It is in the first situation only that it is possible to examine the anatomical characters of this substance. It is sufficiently similar to fat or animal oil in other parts of the body, to lead us to refer it to that head. In other respects its chemical qualities have not been much examined; but an analysis by Berzelius shows that it consists chiefly of an oily matter, not unlike butter in general properties. The filaments, blood-vessels, albumen, gelatin, and osmazome found by this chemist in marrow, and which did not exceed 4 parts in the 100, are derived from the filamentous tissue, in which the medullary particles are deposited.
Medullary membrane. The medullary membrane, which has been considered as an internal periosteum, is imperfectly known. There can be no doubt, however, of its existence, which is demonstrated by opening transversely or longitudinally the medullary canal of a long bone, and boiling it for about two hours. The marrow then drops out; and it will be found to be deposited in the interstices of a filamentous net-work of animal matter, like fine cellular tissue, which may be traced not only into the lattice-work of the extremities, but into the longitudinal canals of the cylindrical bones. It is traversed by blood-vessels, which are observed to bleed during amputation. No nerves have been found in it. The medullary membrane, in short, may be regarded as an extensive net-work of very minute capillaries united by delicate filamentous tissue. From these capillaries the marrow is deposited as a secretion. (Mascagni, Howship.)
Development. 3. The progressive formation of the osseous system has given rise to many researches by Kerckringius, Vater, Baster, Duhamel, Nesbitt, Haller, Dethleef, Reichel, Albins, John Hunter, Scarpa, Senff, Troja, Meckel, Howship, Medici, Serres, Lebel, Schultze, Bechard, and Dutrochet; and it is a proof of the complicated nature of the subject, that it continues to give rise to fresh investigation. The inquiry resolves itself into two parts,—the history of the process of ossification as it takes place originally in the fetus and infant, and the history of its progress as a process of repair when bones are divided, broken, or otherwise destroyed or removed.
From the first formation of the embryo to the termination of fetal existence, and thenceforth to the completion of growth, the bones undergo changes in which various stages may be distinguished. In the first weeks of fetal existence it is impossible to recognise any thing like bone; and the points in which the bones are afterwards to be developed consist of a soft homogeneous mass of animal matter, which has been designated under the general name of mucus. Some time between the fifth and the seventh week, in the situation of the extremities, may be recognised dark opaque spots, which are firmer and more solid than the surrounding animal matter. About the eighth week, the extremities may be seen to consist of their component parts, in the centre of each of which is a cylindrical piece of bony matter. Dark solid specks are also seen in the spine, corresponding to the bodies of the vertebrae; and even the rudiments of spinous processes are observed in the shape of minute dark points. In the hands and feet rings of bone are seen in the site of the metacarpal and metatarsal bones. All the joints consist of a semi-consistent jelly-like matter, liberally supplied by blood-vessels. At ten weeks the cylinders and rings are increased in length, and are observed to approach the jelly-like extremities, which are acquiring the consistence of cartilage, and when divided present irregular cavities. At the same time the parts forming the head are highly vascular; and between the membranes are deposited minute points of bony matter, proceeding in rays from a centre, which, however, is thinner and more transparent than the margin. (Howship.)
Between thirteen weeks and four months the cavities in the jelly-like cartilaginous matter receive injection. The membranes of the head are highly vascular, transmitting their vessels through the intervals of the osseous rays, which are occupied abundantly by stiff, glairy, colourless, mucilaginous fluid.
In the seventh month the bony cylinder of the thigh-bone and its epiphyses contain canals perceptible to the microscope. In the head the bones are proceeding to completion; the pericranium and dura mater are highly vascular; and a quantity of reddish semitransparent jelly between the scalp and the skull, which contain numerous minute vessels, Mr Howship regards as the loose cellular state of the fetal pericranium. This is, however, doubtful. The cylindrical bones have at this period no medullary cavity, but present in their interior a loose bony texture.
Between the seventh and eighth months, in a fetus ten inches long, the humerus consists of a cylinder of bone placed between two brownish, firm, jelly-like masses, which correspond to the epiphyses, inclosed by periosteum, which adheres loosely by means of filamentous and vascular productions. The radius is a thin bony rod, also between two jelly-like epiphyses. The ulna is still thinner, more slender and flexible, and even compressible. The intersosseous ligament is a continuous duplicature of the periosteum. The metacarpal bones are much as before, only larger. The hands and fingers are complete; but the phalanges consist of minute semi-hard grains, inclosed in periosteum, which forms a general sac to them, and to the intermediate connecting parts. The middle and ungual phalanges can scarcely be called osseous. The femur, like the humerus, is an osseous cylinder between two jelly-like epiphyses, enveloped in loosely adhering periosteum. The tibia and fibula are like the radius and ulna. The metatarsal bones are cylindrical pieces, firm, but not very hard. The first phalanx of the toes is complete; the other two, though the toes are fully formed, are much of the consist- General ence of cartilage. The carpal and tarsal bones are in the state of the epiphyses, but of a gray colour.
In this state of the osseous system, the periosteum, which is continuous, and appears to make one membrane with the capsular ligaments and the deep-seated portions of the fascia, adheres to the bone chiefly by arteries and filamentous productions; and so loose is this connection, that a probe may be inserted beneath it, and carried round or inwards, unless where these connections are situate. Another point where the periosteum adheres firmly is at muscular insertions, to the humerus at the insertion of the deltoid, and to the femur at that of the gluteus.
In the vertebral column the bodies of the vertebrae and the spinous plates are formed; and minute specks are beginning in the site of the transverse processes.
In the skull the parietal bones are well-formed shells of bone, though very deficient at the mesial plane, the anterior margin, and the upper anterior angle. The pericranium is distinctly membranous and vascular; and the red jelly-like fluid noticed by Mr Howship is exterior to this membrane.
At the period of birth the cylindrical bones contain tubular canals filled with a colourless gelatinous fluid, and terminating in the surface of ossification. As the bones previous to this period are homogeneous, and contain no distinct medullary cavity, but present in their interior a soft or loose bony texture, it is reasonable to suppose that the development of the longitudinal canals is connected with the formation of the medullary cavity. At birth, in the femur may be distinguished a medullary cavity beginning to be formed, about half a line broad, but still very imperfect.
After birth, the two processes of the formation of tubular canals and medullary cavity go on simultaneously; and at the same rate nearly, the outer part of the cylindrical bones acquires a more dense and compact appearance. The epiphyses, also, which are in the shape of grayish jelly-like masses, begin to present grains and points of bone. Previously to this, Mr Howship represents them, while still cartilaginous, as penetrated by canals or tubes, which gradually disappear as ossification proceeds. The carpal and tarsal bones appear to observe the same course in the process of ossification.
In the bones of the skull, however, a different law is observed. The osseous matter is originally deposited in linear tracts or fibres, radiating or diverging from certain points termed centres of ossification. Each bone is completed in one shell without diploe or distinguishable table.
Afterwards, when they are completed laterally, or in the radiating direction, the cancellated arrangement of the diploe begins to take place apparently in the same manner in which the medullary cavity and compact parts of the long bones are formed.
In the process now described, it is important to observe that the bony matter is deposited round the soft parts, and that the cavities, holes, and canals of bones are merely parts in which the previous existence of vessels, nerves, ligaments, or tendons, prevents the subsequent formation of bone.
It has been generally supposed that the formation of cartilage is a preliminary step to that of bone. This, however, seems to be a mistake, arising from the circumstance that cartilage is often observed to be converted in the living body into bone. Neither in the long nor in the flat bones is anything like cartilage at any time observed. The epiphyses, indeed, present something of the consistence of cartilage, but it has neither the firmness nor the elasticity of that substance. It is a concrete jelly, afterwards to be penetrated by calcareous matter. The flat bones are from the first osseous; and though their margins are soft and flexible, in consequence of their recent formation and moist state, they have still a distinct osseous appearance and arrangement, and bear no resemblance to cartilage. In short, true bone seems never at any period of its growth to be cartilaginous.
The progressive growth of bones is effected by accretion of new matter to their extremities. The cylindrical bones elongate by the addition of new matter to the extremities of their diaphyses, and the flat bones by the enlargement of their margins. The latter fact is established by simple inspection during the process of ossification of the cranial bones. In proof of the former, the experiment of John Hunter is decisive. In the tibia of a pig he bored two holes, one near the upper, the other near the lower end, with an interval of two inches exactly, and inserted into each hole a small leaden shot. After some time, when the animal had grown, and the length of the bone was increased, on killing it, the space between the leaden shots was found, as at first, to be exactly two inches,—thereby showing that no elongation had taken place between the perforations. The experiment was often repeated with the same result.
The period at which ossification is completed varies in different individuals. It may be said to be indicated by the completion of the medullary canal, by the ossification of the epiphyses, and their perfect union with the osseous cylinder (diaphysis). The first circumstance is indefinite. The two latter, though more fixed, are still liable to great variation. The epiphyses are rarely united before the age of 14 or 15; and they may continue detached to the 20th or 21st year. In general, however, they begin to unite or to be knit, as is said, between the 15th and 20th years.
That the main agents of original ossification are the periosteum and its arteries, the proofs are manifest. The formation of bone can be ascribed to the vessels of two agents only,—the periosteum and the medullary membrane. That the latter is not concerned in the production of bone in the fetus, must be inferred from the fact that at that period it cannot be said to exist. To the periosteum, therefore, and its vessels must be ascribed the process of fetal ossification. Of this a cumulative proof is found in the circumstance, that the periosteum adheres more firmly at the ends than the middle of the bones; and that the pericranium and dura mater, which perform the part of periosteum to the bones of the skull, are visibly concerned in the formation and successive enlargement of these bones. But though the periosteal vessels are the main agents of ossification originally, there is reason to believe that the medullary vessels contribute to its growth and nutrition after it is formed. This may be inferred from the phenomena of fractures, of diseases of the bones, and of those experiments in which the medullary membrane is injured. The periosteum, however, does not act by ossification of its inner layers, as Duhamel, misled by a false analogy between the growth of trees and bones, laboured to establish.
A peculiar form of the osseous system requiring notice are the sesamoid bones. These, which derive their name from their minuteness, (σεσαμος, a grain), most of them, excepting the knee-pan, being of the size of a grain or pea, are confined to the extremities, and are situate chiefly in positions in which they give points of support to the tendons of the flexor muscles. (Tendons of the gemelli, tibialis posticus, peronaeus longus, &c.) The peculiarity of these bones is, that they are formed invariably in the substance of fibrous organs, as tendons in the case of the knee-pan and the sesamoid bones of the gemelli, tibialis posticus, and peronaeus longus; or ligaments General in the case of those situate between the chiro-phalangeal and podo-phalangeal articulations. With this peculiarity their mode of ossification corresponds. At first albuminous or fibro-albuminous, in process of time they are penetrated by calcareous matter, and present an osseous texture, which, however, is much less firm than that of genuine bone. The period at which this deposition commences and is completed varies in different individuals; and hence scarcely in any two persons of the same age is the number of sesamoid bones the same. Though the patella may be ossified at the 20th year, the minute sesamoid bones are sometimes not formed before the 30th or even the 40th. In the patella, when ossified, we find a medullary organ; but it is uncertain whether the others acquire this mark of osseous character. These bones resemble the epiphyses in uniting, when divided, by fibro-albuminous matter.
4. The bones of which the skeleton consists are united in two modes: 1st, by movable junction (diarthrosis); 2dly, by immovable junction (synarthrosis). Both modes of union bear the general name of articulation, though this term would with greater propriety be confined to the first or movable union. By this are connected all the bones concerned in locomotion, and some of those devoted to the organic functions, as the ribs and the lower jaw. The second is employed in the union of bones forming the walls of cavities.
In the movable union, the articular surfaces are united in two modes. In the first, in which one bone moves on the other with different degrees of freedom, the articular surfaces are covered by cartilage and synovial membrane, and the bones are united by ligaments and tendons. In the second (amphiarthrosis), in which the motion is confined to a species of torsion or imperfect rotation, the bones are united without articular surface by fibro-cartilage. The first is exemplified in the articulations of the extremities; the second is seen in the union of the bodies of the vertebrae and the bones of the pelvis.
The several forms of movable union with free motion, or articulations proper, may be referred to four heads, according to the nature of the motions performed. The first is the motion of radio-central opposition, or pivot-motion in every direction, in which the bone moves in its articular cavity, not only backwards and forwards, or by flexion and extension, but by abduction and adduction, and, by the succession of these motions, may describe a cone with the apex at the joint, or what is termed circumduction. This most extensive form of motion is found in the scapulo-humeral and coxo-femoral articulations only. The second form of articular motion is antero-posterior opposition, or cardinal motion (cardo, a hinge), in which the bones move on each other by flexion and extension, as a gate on its hinges. This, which is sometimes named limited opposition, is found in the femoro-tibial and humero-cubital joints, and all those which undergo flexion and extension. The third form of motion is that of rotation, in which the bone revolves on its axis,—an infrequent variety, confined chiefly to the humerus and femur. The fourth, which is the gliding motion, though common to all articular surfaces, is nevertheless the peculiar motion of the carpal and tarsal bones.
In the immovable union the surfaces are united in three modes. The first is by mutual indentation, or what is named suture (sutura vera), in which the margin of one bone is dovetailed by alternate serrated teeth and notches, into that of another. The second is by juxtaposition (harmonia), in which the margin of one bone is simply fitted to that of another. A peculiar variety of this is, when the acute margin of one bone is received between the bifid margin of another, as the axygos process of the sphenoid bone is received by the plates of the corner; (schindylaxis.) The third mode of immovable union is by implantation or insertion (gomphosis), as the teeth are inserted into the alveolar cavities of the superior and inferior maxillary bones.
The following table exhibits a view of these modes of junction, with their appropriate appellations.
**JUNCTIONS OF BONES.**
I. IMMMOVABLE; (SYNARTHROSIS.)
Continuous Bony Surfaces, united by Bone and Membrane.
| Mutual Indentation | Sutura | |-------------------|--------| | | | | | |
II. SEMIMOVABLE; (AMPHIARTHROSIS.)
Continuous Surfaces, united by Fibro-Cartilage.
| Rotation and Torsion | A. Rotatio. | |---------------------|-------------| | Cardinal Opposition | A. Lateralis |
III. MOVABLE; (DIARTHROSIS.)
Contiguous, Cartilaginous Surfaces, united by Ligaments.
| Unlimited Opposition, Circumduction, and Rotation. | |--------------------------------------------------| | Unlimited Opposition, and Circumduction. | | Limited Opposition, Flexion, and Extension. | | Rotation. | | Gliding. |
Teeth. (Dentes.)
Every tooth consists of two hard parts; one external, Teeth white, uniform, somewhat like ivory; the other internal, similar to the compact structure of bone.
The first, which is named enamel, is seen only at the crown of the tooth, the upper and outer part of which consists of this substance. It is white, very close in texture, perfectly uniform and homogeneous, yet presenting a fibrous arrangement. Extending across the summit of the tooth in the manner of an incrustation, it is thick above, and diminishes gradually to the root, where it disappears. This fact is demonstrated by macerating a tooth in dilute nitric acid, when the bony root becomes yellow, while the crown remains white.
The enamel is not injectible, and is therefore believed to be inorganic. It is also filed and broken without being reproduced; nor does it present any of the usual properties which distinguish organized bodies. The piercing sensation which is communicated through the tooth from the impression of acids seems to depend on the mere chemical operation, and not on the physiological effect. General Anatomy. Teeth.
The whole, the enamel is to be viewed as the inorganic result of a process of secretion or deposition.
The bony part of the tooth is the root and that internal part which is covered on the sides and above by the enamel. It consists of close-grained bony matter, as dense as the compact walls of the long bones, or the petrous portion of the temporal bone. The fibres which are said to be seen in it are exactly of the same nature as those in bone.
In the interior of the bony part of each tooth is a cavity which descends into the root, and communicates at its extremity with the outer surface by openings corresponding with the number of branches into which the root is divided. This cavity, which is large in young or newly formed teeth, and small in those which are old, contains a delicate vascular membrane, which has been named the pulp of the tooth. It is best seen by breaking a recent tooth by a smart blow with a hammer, when the soft pulpy membrane may be picked out of the fragments by the forceps. It then appears to be a membranous web with two surfaces, an exterior adhering to the bony surface of the dental cavity by minute vessels; the other interior, free, and, so far as can be determined of a body so minute, resembling a closed sac.
The development and growth of the teeth is a process of much interest.
At what time the first rudiments of teeth appear seems not to be determined with accuracy. In the fetus, between the seventh and eighth month, I can merely distinguish in the centre of the vascular membrane of the alveolar cavity a minute firm body like a seed. I have, however, seen the crowns of teeth formed in foetuses which, I have reason to believe, had not attained the seventh month. But whatever may be the exact period, the process is nearly as follows.
While the bones of the upper and lower jaw are in the process of formation between the third and fourth months, (fourth and fifth, Bichat, tom. iii. p. 93,) a series of soft, membranous, vascular sacs inclosed within the general cavity of the periosteum, may be recognised at their lower and upper margins, which are still without those osseous plates which afterwards constitute the alveoli. Each of the sacs now mentioned consists, like a serous membrane, of two divisions,—one external, attached to the periosteum, the other folded within it, and forming a closed cavity. The outer or periosteal deposits in the intervals between each sac, bone, which eventually constitutes the transverse septa of the alveoli. From the inside of the inflected portion the process of dentition commences some time between the fifth and seventh month, by the deposition of matter from the vessels at the lowest point of the alveolar division of the sac. This matter is to constitute the crown of the tooth, which is invariably formed first. After the deposition of the first portions, these are pushed upwards by the addition of successive layers below them, and necessarily carry the inflected part of the sac before them. As this process of deposition advances, the tooth gradually fills the sac, and rises till it reaches the level of the alveolar margins. If a tooth be examined in situ, near the period of birth, it is found to consist of the crown, with portions of enamel descending on every side, and forming a cavity in which a cluster of blood-vessels proceeding from the sac is lodged. In the mean time, bone is deposited from the periosteal division all round each sac, so as to form the alveoli.
After the enamel has been deposited the bone begins to be formed; and as this process advances, the tooth is still forcibly thrust upwards by the addition of matter to its root. When the latter is well completed, the vessels become smaller and less abundant, until, when the tooth is perfect, they shrink to a mere membrane, which lines the cavity of the tooth, and still maintains its original connection with the alveolar membrane, by the minute vascular production which enters the orifice or orifices of the root.
Physiological authors have thought it important to mark the period at which the teeth appear at the gums; and in general this takes place about the sixth or seventh month after birth. This mode of viewing the process of dentition, however, gives rise to numberless mistakes on the period of teething. The process, as we see, commences in the early period of fetal existence; and the time at which they appear above the gums varies according to the progress made in the womb. In some the process is rapid, in others it is tardy; and even the stories of Richard III. and Louis XIV. receive confirmation from the fact of 19 examples cited by Haller, of infants born with one or more teeth above the gum. Generally speaking, the crown is completed at the period of birth; and, according as the formation of the root advances with rapidity or slowly, dentition is early or late.
What is here described is the process of the formation of the first or temporary set of teeth, which consist, it is well known, of twenty. In that of the second set the same course is observed. In the same manner is observed a row of follicular sacs, though not exactly in the original alveoli, yet attached to the sacs of the temporary teeth by vascular membranes; in the same manner deposition begins at the bottom of the free surface of the sac by the formation of the crown; and in the same manner the crown is forcibly raised by the successive accretion of new matter to its base. The moment this process commences, a new train of phenomena takes place with the primary teeth. The follicular sacs of the new or permanent teeth are liberally supplied with vessels for the purpose of nutrition; and as these blood-vessels increase in size, those of the temporary teeth diminish; and the supply of blood being thus cut off, the latter undergo a sort of natural death. The roots which, as being last formed, are not unfrequently incomplete, now undergo a process of absorption; and the tooth drops out in consequence of the destruction of its nutritious vessels. Some authors have ascribed this expulsion to pressure, exercised by the new tooth. They forget, however, that before the new tooth can exert any pressure, it must be in some degree formed; and to this a vascular system is indispensable.
The increased number of the teeth when permanent, the enlargement of the jaws, and the consequent expansion of the face, though interesting, are foreign to the present inquiry.
Gristle, Cartilage. (Cartilago.—Tissu Cartilagineux.)
The cartilaginous system or tissue is found at least in three different situations of the human body; 1st, on the articular extremities of the movable bones; 2d, on the connecting surfaces or margins of immovable bones; 3d, in the parietes of certain cavities, the motions and uses of which require bodies of this elastic substance.
The organization of gristle is obscure and indistinct. On examination by the microscope, its surface is pearl-white, uniform and homogeneous, firm and glistening, with numerous minute pores. William Hunter represents the articular cartilages as consisting of longitudinal and transverse fibres. (Phil. Trans. vol. xlii.) Herissant represents those of the ribs as composed of minute fibres mutually aggregated into bundles connected by short slips, and twisted in a spiral or serpentine direction. (Mém. de l'Acad. 1748.) By Delsonne, the articular cartilages... General are said to consist of a multitude of minute threads, mutually connected and placed at right angles to the plane of the bone, but so as to radiate from the centre to the circumference. (Ibid. 1752.) The general fact of fibrous structure is confirmed by Bichat, who states that it is possible to recognize longitudinal fibres, which are intersected by others, oblique or transverse, but without determinate order. In its purest form no blood-vessels are seen in it, nor can they be demonstrated by the finest injections. In the margins of those pieces of gristle, however, which are attached to the extremities of growing bones, blood-vessels of considerable size may often be seen, even without the aid of injection. In young subjects a net-work of arteries and veins, which is described by Hunter under the name of *circulus articuli ossculosus*, may be demonstrated all round the margin of the cartilage at the line between the epiphysis and it. They terminate so abruptly, however, that they cannot be traced into the substance of the latter. The most certain proofs, however, of the organic structure of this substance are the serous exudation which appears in a few seconds on the surface of a piece of cartilage after division by the knife; and the fact that it becomes yellow during jaundice, and derives colour from substances found in the blood. Neither absorbents nor nerves have been found in it. The cellular texture said by Bichat to form the mould for the proper cartilaginous matter appears to be imaginary.
The articular cartilages adhere to the epiphyses by one surface, which consists of short perpendicular fibres placed parallel to each other, and forming a structure like the pile of velvet. This is easily demonstrated by maceration, first in nitric acid, and then in water. The free or smooth surface is covered by a thin fold of synovial membrane, which comes off in pieces during maceration. The existence of this, though recently denied by Gordon, was admitted by William Hunter, and may be demonstrated either by boiling, maceration, or the phenomena of inflammation, under which it is sensibly thickened. All other cartilages are enveloped, unless where they are attached to bones, by a fibrous membrane, which has been therefore named *perichondrium*. The existence of this may be demonstrated by dissection, and also by boiling, which makes it peel off in crisped flakes.
The chemical properties of cartilage have not been accurately examined. Boiling shows that it contains gelatine; but as much of the matter is undissolved, it may be inferred that it is under some modification, or united with some other principle, perhaps albumen. Immersion in nitric acid or boiling fluids induces crispation, and it dries hard and semitransparent like horn.
**Fibro-Cartilage, Chondro-Dermoid Texture. (Cartilago Fibrosa.—Tissu Fibro-Cartilagineux.)**
Intermediate between the cartilaginous and the fibrous tissues, Bichat ranks that of the fibro-cartilages, which comprehends three subdivisions: 1st, the membranous fibro-cartilages, as those of the ears, nose, windpipe, eyelids, &c.; 2d, the inter-articular fibro-cartilages, as those found in the temporomaxillary and femoro-tibial articulations, the intervertebral substances, and the cartilaginous bodies uniting the bones of the pelvis; 3d, certain portions of the periosteum, in which, when a tendinous sheath is formed, the peculiar nature of the fibrous system disappears, and is succeeded by a substance belonging to the order of fibro-cartilages.
Beclard follows Meckel in rejecting the first subdivision, the individuals of which are quite similar to ordinary cartilage, in wanting the distinct fibrous structure, and being covered by perichondrium, the fibres of which have caused them to be regarded as fibro-cartilages. On this principle Beclard gives the following view of the fibro-cartilages:
1st, Fibro-cartilages free at both surfaces; those in the form of menisci, which are placed between the articular surfaces of two bones (*fibro-cartilagines inter-articulares*). These are seen in the temporomaxillary, sterno-clavicular, and femoro-tibial articulations, and occasionally in the acromio-clavicular and the ulno-carpal joints. These ligaments are attached either by their margins or their extremities, and are enveloped in a thin fold of synovial membrane. 2d, Fibro-cartilages attached by one surface. Of this description are those employed as pulleys or grooves for the easy motion of tendons; for instance, the chondro-desmoid eminences attached to the margin of the glenoid cavity for the long head of the biceps, and at the sinuosity of the ischium for the tendons of the obturators. 3d, Fibro-cartilages, which establish a connection between bones susceptible of little individual motion, as the intervertebral bodies; or which unite bones intended to remain fixed, unless under very peculiar circumstances, as those which form the junction of the pelvic bones. (Symphysis pubis; sacro-iliac synchondrosis.)
The peculiarities of these substances consist in their partaking in different proportions of the nature of cartilage and white fibrous tissue, and, consequently, in possessing the toughness and resistance of the latter with the elasticity and flexibility of the former. The structure of the fibro-cartilaginous tissue is easily seen in the intervertebral bodies, and in the cartilages uniting the pelvic bones. In the former, white concentric layers, consisting of circular fibres placed in juxtaposition, constitute the outer part, while the interior contains a semifluid jelly. The concentric fibrous layers are cartilage in a fibrous shape. In the latter situation the fibrous structure is equally distinct, while the cartilaginous consistence shows the connection with that organic substance. A similar arrangement is remarked in the inter-articular cartilage of the temporomaxillary articulation, and in the semilunar cartilages of the knee-joint. In all, the fibrous is said to predominate over the cartilaginous structure. Their physical properties are distensibility and elasticity. Though they are at all times subjected to considerable pressure, they speedily recover their former size. Though their chemical composition is not exactly known, they evidently contain much gelatine.
**Gland. Glandular System. (Glandula.)**
The name gland, though rather vaguely used, may be properly restricted to designate organs of a definite structure, consisting of arteries, veins, and excretory tubes, arranged in a peculiar manner, and destined to separate from the blood a fluid of peculiar chemical and physiological properties. The organs of this description may be arranged in two general divisions,—the follicular glands, or those which occur in an isolated form; and the conglomerate glands, or those which, being of larger volume, are understood to consist of numerous small glands combined in one general organ. The former embraces the sebaceous glands of the skin and the muciparous glands of mucous membranes; in the latter are comprehended the lacrymal and salivary glands, with the tonsils, the pancreas, the liver, the kidneys, the testicles of the male, and mammae of the female, and perhaps the prostate gland. To a third head, denominated that of imperfect glands, Meckel refers such organs as the thymus, the suprarenal capsules, the thyroid, and the spleen. But since the term imperfect implies here a contradiction, and since it is by no means ascer- tained, either that these organs secrete, or that their secretions are removed by the lymphatics, it is manifest that they cannot be justly associated with the organs above defined as examples of glands.
The follicular glands, though most minute, are nevertheless distinguished by the most simple and intelligible structure. They consist of small hollow spherical sacs, or minute membranes moulded into the saccular form, in the attached surface of which are distributed numerous minute arteries and veins, and the free surface of which is smooth and covered with the fluid secreted. The quantity of vascular substance with filamentous tissue surrounding the attached surface of these glands, makes them occasionally project from the surface of the membrane to which they are attached. In ordinary circumstances, however, they cause no elevation, and appear in the form of simple sacs with a narrow orifice. These glands belong to two textures only of the animal body—the skin and the mucous membrane. In the former they are named sebaceous glands, from the fluid which they secrete containing a small portion of fatty matter. In the latter they are named follicles, crypts, or muciparous glands.
In certain regions of the mucous membranes, for instance in the male urethra, the crypts are arranged in such a manner that they constitute large sinuous cavities, the free surface of which secretes serous mucus copiously. These cavities, which have the further effect of increasing much the superficial extent of the membrane, are denominated lacunae. The peculiarity of this form of mucous gland appears to consist in its membranous sac having unusual extent, and consequently in the glandular vessels being more expanded than in the ordinary glands.
The structure of the conglomerate glands is more complicated. Each gland consists of numerous minute portions of definite figure, named lobules; and each lobule may be resolved into granules, also of definite shape, intimately connected by filamentous tissue. These granules, which have since the time of Malpighi been denominated acini, are found to consist of clusters of minute arteries and veins aggregated together, with minute tubes for conveying away the secreted fluid. On these points anatomists are agreed. They are seen most distinctly in the liver and kidney, and may be demonstrated in the pancreas, testicles, and female breast, by injection. Every acinus, in short, may be said to consist of two parts, a vascular or supplying, and a tubular or excreting.
On the manner in which these two parts of the acinus communicate, however, there is less certainty and precision. In this difficulty, as the point is scarcely a matter of observation, conjecture has been resorted to; and the opinions of anatomists have been divided between two parties. According to one, at the head of which may be placed Ruysch, Haller, William Hunter, and Hewson, the minute arteries terminate directly in the excretory ducts, without intermediate substance. According to the other opinion, which is that of Malpighi, between the arteries and the excretory tubes there are placed minute membranous vesiculae or pouches, in the substance of which the arteries, still more minutely divided, are distributed, and from the free surface of which the process of secretion goes on. In short, each acinus, according to Malpighi, is a separate follicle, and the conglomerate glands consist merely of numerous follicles, combined so as to form a large general secreting organ.
Between these two views of the intimate nature of the glandular tissue there is less difference than at first sight might be imagined. The chief difference is in the ultimate arrangement of the glandular capillaries. According to the view of Malpighi, these capillaries are arranged in clusters, as it were, round the beginning of the excretory pore, so that even in this condition the termination of the former class of vessels is the commencement of the latter. Conversely, it may be said, that since the delicate membrane in which the secreted fluid first appears necessarily receives the capillary terminations, the latter cannot be said to communicate directly with the excretory tubes. The correct view of the matter is, that by the term vesicles are not to be understood large sacs, but merely the rounded recess of the membrane which forms the excretory tubes. Further, since the researches of Hewson and Monro show that in the kidney and the testicle the arteries are convoluted, it may be inferred that this is the character of the capillary arrangement of the glands; and that it is requisite to the performance of the process of secretion that the vessels be disposed in such a tortuous manner as to prevent too rapid motion of the blood.
The conglomerate glands, we have seen, consist chiefly of minute vascular ramifications infinitely subdivided. In all the glands, excepting the liver, these vessels consist of arteries to convey blood to the organ, and veins to return it to the system; and in all the glands, excepting the liver, it is a peculiar circumstance that the same arterial trunk conveys blood for nourishing the gland, and for supplying the materials of the secretion. All the secretions, therefore, excepting that of the liver, are derived from arterial blood. The liver alone, besides receiving a considerable artery, derived from the celiac trunk, is remarkable for being chiefly supplied with blood from a large venous trunk, formed by the union of the veins of the stomach and spleen, and the mesenteric and mesocele branches, and which after this union is again subdivided into ramifications in the substance of the gland. Injection shows that the branches and twigs of this vein anastomose freely with those of the hepatic artery; and though it might be imagined that the latter is intended chiefly to nourish the gland, and the former to supply the materials for secretion, this circumstance, with the fact that in some rare instances the vena porta is not distributed in the liver, shows that at present this opinion must be adopted with caution.
Besides arteries, veins, and excretory tubes, glands are supplied with lymphatic vessels, which are arranged in two sets, superficial and deep. The former are confined to the surface of the organ, over which they may be seen creeping in every direction, and belong chiefly to the membranous coverings of the glands. The deep-seated lymphatics are those which penetrate the substance of the glands, and in general accompany the large blood-vessels.
Every gland receives a proportion of nervous branches, generally from the nerves of the sympathetic system. These branches accompany the blood-vessels in penetrating the substance of the glands, and are distributed much in the same manner as the arteries before their ultimate division. They exercise some influence over the process of secretion; but the nature and extent of this influence are still undetermined.
Each gland contains a quantity of filamentous tissue, which envelopes the blood-vessels, tubes, lymphatics, and nerves, and constitutes a large proportion of the mass of the gland. The simple tissues, thus united, are inclosed in a general membranous covering, which also partly contributes with these tissues to retain it in its situation. These membranous coverings vary in different glands. In the liver and pancreas it is the peritoneum; the kidneys are inclosed in a peculiar tunic; the testes are contained in a fibrous membrane; and the acini of the lacrymal General and mammary glands appear to be covered by a form of condensed filamentous tissue.
**CHAP. III.—ENVELOPING TISSUES.**
*Skin.* (Cutis, Pollis.) *Cutaneous Tissue, Dermal Tissue.* (La Peau, Tissu Dermoidé,—Die Haut, Das Fell.) *Fell,* old English; with its appendages, Scarf-skin or Cuticle, Nail, Hair. (Cuticula, Epidermis,—Tissu Epidermoïde et Tissu Pileux.)
Skin has been said to consist of three parts, true skin (*cutis vera*), mucous net (*rete mucosum*), and scarf-skin or cuticle. Haller, Camper, and Blumenbach, are inclined to deny the existence of the mucous net in the skin of the white, and to admit it in that of the negro only; and in point of fact, indeed, its existence has been demonstrated in the negro race only, and inferred by analogy to exist in the white. "When a blister has been applied to the skin of a negro," says Cruikshank, "if it has not been very stimulating, in twelve hours after a thin transparent grayish membrane is raised, under which we find a fluid. This membrane is the cuticle or scarf-skin. When this with the fluid is removed, the surface under these appears black; but if the blister had been very stimulating, another membrane, in which this black colour resides, would also have been raised with the cuticle. This is *rete mucosum*, which is itself double, consisting of another gray transparent membrane, and of a black web very much resembling the *pigmentum nigrum* of the eye. When this membrane is removed, the surface of the true skin, as has been hitherto believed, comes in view, and is white like that of a European. The *rete mucosum* gives the colour to the skin; is black in the negro; white, brown, or yellowish in the European." (Experiments on the Insensible Perspiration, &c. London, 1795.)
Bichat denies the existence of a mucous varnish (*corpus mucosum*) such as Malpighi describes it, and regards the vascular surface of the corion as the only mucous net.
According to Chaussier the skin consists of two parts only, the *derma* (*séqua, cutis vera*) or corion, and the *epidermis*, cuticle, or scarf-skin; the first embracing the organic elements of this tissue; the second being an inorganic substance prepared by the organic, and deposited on its surface. This opinion is adopted by Gordon, according to whom the skin consists of two substances placed above each other, like layers or plates (*laminae*), the inner of which is the true skin, the outer the cuticle or scarf-skin. Beclaud, on the contrary, thinks that a peculiar matter, which occasions the colour by which the several races are distinguished, is found between the outer surface of the corion and the cuticle; and that no fair race is destitute of it except the albino, the peculiar appearance of whom he ascribes to the absence of the mucous net of the skin.
The corion of the human skin (*pollis, corium, derma, cutis vera*) seems to consist chiefly of very small dense fibres, not unlike those of the proper arterial coat, closely interwoven with each other, and more firmly compacted the nearer they are to its outer or cuticular surface. The inner surface of the corion is of a gray colour; and in almost all parts of the body presents a number of depressions varying in size from $\frac{1}{4}$th to $\frac{1}{6}$th of an inch, and consequently forming spaces or intervals between them. These depressions, which correspond to eminences in the subjacent adipose tissue, have been termed *areolae*. They are wanting in the corion of the back of the hand and foot only.
The outer or cuticular surface of the corion is smooth, of a pale or flesh-red tinge, and is much more vascular than its inner surface. It presents further a number of minute conical eminences (*papillae*), which, according to the recent observations of Gautier and Dutrochet, are liberally supplied with blood-vessels, and are the most vascular part of this membrane. In the ordinary state of circulation and temperature during life these eminences are on a level with the surrounding corion; but when the surface is chilled, this membrane shrinks, while the papillae either continue unchanged or shrink less proportionally, and give rise to the appearance described under the name of goose skin (*cutis anserina*). This surface was said by the older anatomists to present numerous orifices or pores; but according to Gordon, if we trust to observation, no openings of this kind can be recognised, either by the eye or the microscope, except those of the sebaceous follicles. The hairs, indeed, are found to issue from holes in the corion, but they fill them completely.
In certain situations, for instance at the entrance of the external auditory hole, at the tip of the nose, on the margins of the eyelids, in the armpits, at the nipple, at the skin of the pubes, round the anus and the female pudendum, are placed minute orifices, from which exudes an oleaginous fluid, which is quickly indurated. These openings lead into the cavities of small sacs called follicles (*folliculi*) or sebaceous glands (*glandula sebacea*). These sacs, the structure of which is noticed above, consist of hollow surfaces secreting an oleaginous fluid, which is progressively propelled to the orifice, where it soon undergoes that partial inspissation which gives it the sebaceous or suet-like aspect and consistence.
The corion is liberally supplied with blood-vessels, nerves, and absorbents. After a successful injection, its outer surface appears to consist of a uniform net-work of minute vessels, subdivided to an infinite degree of delicacy, and containing during life blood coloured and colourless. It can scarcely be doubted that this vascular net-work (*rete vasculorum*) is the only texture corresponding to the reticular body of the older anatomists.
It is well known that this membrane, when boiled sufficiently long, is converted into a viscid glutinous liquor, which consists chiefly of gelatine (Chaptal, Seguin, Hattchett, Vauquelin, &c.), and that glue is obtained from it for the purposes of art. As, however, in these operations a portion of matter is left undissolved, and as glue is completely soluble in water, while skin resists it for an indefinite time, it may be concluded, that though the chief constituent of the corion is gelatine, it is under some peculiar modification not perfectly understood. The union of this organized gelatine with the vegetable principle denominated *tannin* forms leather, which is insoluble in water.
Cuticle or scarf-skin (*epidermis, cuticula*) is a semi-transparent, or rather translucent layer of thin light-coloured matter, extended continuously over the outer surface of the corion. Its thickness varies, being thinnest in those parts least exposed to pressure and friction, but thickest in the palms and soles. It is destitute of blood-vessels, nerves, and absorbents; and there is reason to believe, from observing the phenomena of its reproduction, that it is originally secreted in the form of a semifluid viscid matter by the outer surface of the corion; and that, as it is successively worn or removed by attrition, it is in like manner replaced by a constant process of secretory deposition. This semifluid viscid matter, which in truth is found between the outer surface of the corion and the firm cuticle, is the substance mentioned by Malpighi, and so often spoken of as the mucous net (*corpus mucosum*). It is inorganic; and it is impossible to explain its production otherwise than by ascribing it to the outer vascular surface of the corion. Cuticle is rendered yellow and finally dissolved by immersion in nitric acid. It is also dissolved by sulphuric acid in the form of a deep brown pulp. These, and some other experiments performed by Hatchett, show that it consists chiefly of modified albuminous matter.
This description shows, that if strict observation be trusted, the mucous net has no existence, at least in the European. In the Negro, Caffre, and Malay, however, a black membrane is said to be interposed between the corion and cuticle, and to be the cause of the dark complexion of these races. On this subject I refer to the description given by Cruikshank, which is the best (Experiments, &c. p. 31, 41, and 43); the Essay of M. Gautier, already quoted; and the observations of Beclard. What is found in the skin of the mixed or half-caste races, i.e. the offspring of an African and a European, or of a mulatto and European? and how is the transition between this colouring layer and its insensible diminution effected?
Nail is a substance familiarly known. On its nature and structure we find many conjectures, but few or no facts, in the writings of anatomists; and almost all that has been written is the result of analogical inference rather than of direct observation. It is known that the nails drop off with the scarf-skin in the dead body; that they are diseased or destroyed by causes which act on the outer surface of the corion, and produce disease of the cuticle; and that, if forcibly torn out, the surface of the corion to which they were attached bleeds profusely and inflames. In other respects they are inorganic; but these facts warrant the conclusion that the root of the nail is connected with the organic substance of the corion, and that the whole substance is the result of a process of secretion similar to that by which the cuticle is formed.
According to the experiments of Hatchett, they consist of a substance which possesses the properties of coagulated albumen, with a small trace of phosphate of lime.
The root of a hair is not only that part which is contained in the bulb, but the portion which is lodged in the skin. The middle part and the point are those which project beyond the surface of the skin. The bulb is a small sac fixed in the inner surface of the corion, in the contiguous filamentous tissue, and in which the root is implanted.
Every hair is cylindrical, tapering regularly from the root to the point, and solid, but containing its proper colouring matter in its substance. The colour varies, but the root is always whitish and transparent, and softer than the rest; the fixed or adhering part of the root is almost fluid. When hair is decolorized, it becomes transparent and brittle, and presents a peculiar silvery-white colour; and as hairs of this kind are few or abundant, it gives the aspect of gray, hoary, or white hair.
The bulb, though visible in a hair plucked out by the root, is too small in human hair to be minutely examined; and Chirac, Gautier, and Gordon, have therefore described its structure and appearances from the bulbs of the whiskers of large animals, the seal for example, in which it is much more distinct. According to researches of this kind, every bulb forms a sort of sac or follicle, which consists of two tunics, an inner one, tender, vascular, and embracing closely the root of the hair; and an outer, which is firmer and less vascular, and surrounds the inner one, while it adheres to the filamentous tissue and the inner surface of the corion. When the hair issues from the bulb, it passes through an appropriate canal of the corion, which is always more or less oblique, but which, as has been already said, it fills completely; and it afterwards passes in a similar manner through the scarf-skin. Nervous filaments have been traced into the bulbs of the whiskers of the seal by Rudolphi and the younger Andrul. The bulb or follicle, in short, is organic, and forms by secretion the inorganic hair.
The structure of hair appears to be either so simple, or so incapable of being further elucidated, that anatomists have not given any facts of consequence regarding it. Its outer surface is believed to be covered with imbricated scales, because in moving a single hair between the finger and thumb it follows one direction only.
Hair is believed to be utterly inorganic, though the phenomena of its growth, decoloration, and especially of the disease termed Polish plait (plique Polonica), have led various authors to regard it as possessed of some degree of vitality. These phenomena, however, may be explained by the occurrence of disease in the bulbs or generating follicles. Hair is insoluble in boiling water; but Vauquelin succeeded in dissolving it by the aid of Papin's digester. From the experiments of this chemist, and those of Hatchett, it may be inferred that hair consists of an animal matter, which appears to be a modification of albumen, a colouring oil, and some saline substances.
Mucous Membrane, Villous Membrane. (Membrana Mucosa, M. Mucipara, M. Villosa.—Tissu Muqueux, Bichat.)
The organic tissue or membrane to which the name of Mucous mucous or villous has been applied, consists of two great divisions, the gastro-pulmonary and genito-urinary.
The first or gastro-pulmonary division comprehends that membranous surface which commences at the various orifices of the face at which it is contiguous with the skin, and is continued through the lacrymal and nasal passages, and even the Eustachian tube, by the larynx on the one hand to the windpipe and bronchial membrane, and by the oesophagus on the other through the entire tract of the alimentary canal, at the opposite extremity of which it is again identified with the skin.
The distribution of the second division, or the genito-urinary mucous membrane, is slightly varied according to the differences of sex. In the male it is connected with the skin at the orifice of the urethra, from which it proceeds inwards toward the bladder, sending previously small prolongations through ducts on each side of the verum montanum, from which it is believed to be continued through the easa deferentia, to the easa efferentia of the testicle. Continued over the inner surface of the urinary bladder, it is prolonged through the ureters to the pelvis and infundibula of the kidney. In the female, besides passing in this direction, it ascends into the womb, and passes through the Fallopian or uterine tubes, at the upper extremity of which it terminates in an abrupt opening into the sac of the peritoneum—the only instance in the whole body in which a mucous and serous surface communicate freely and directly.
These two orders of membranous tissue have each two surfaces, an attached or adherent, and a free one. The adherent surface is attached, 1st, to muscles, as in the tongue, most of the mouth and fauces, oesophagus, and whole alimentary canal, and the bladder; 2d, to fibrous membranes, as in the nasal cavities and part of the larynx, in which it is attached to periosteum or perichondrium, the palate, ureter, and pelvis of the kidney; 3d, to fibro-cartilages, as in the windpipe (trachea), and bronchial tubes.
The free surface is not uniform or similar throughout. The appearance of the pituitary or Schneiderian mem- brane is different from that of the stomach or intestines; the surface of the tongue and mouth is different from that of the trachea; and the free surface of the urethra is unlike that of the bladder. These variations depend on difference of structure, and are connected with a difference in properties; yet anatomists have improperly applied to the whole what was peculiar to certain parts only, and have thus created a system in which some truth is blended with much misrepresentation.
Mucous membrane consists, like skin, of a corion or derma, and an epidermis or cuticle.
The mucous corion is a firm, dense, gray substance, which forms the ground-work of the membrane in most regions of the body, but which is evidently represented by the fibrous system, e.g., the periosteum or perichondrium, in some other situations. It is most distinctly seen in the mouth and throat, and in various parts of the alimentary canal. In the first situation it is more vascular, less gray and dense, than in the intestinal mucous membrane.
It possesses two surfaces, an inner, adherent to the submucous filamentous tissue, and an outer or proper mucous surface. In the stomach, the mucous corion is in the form of a soft but firm membranous substance, about \( \frac{1}{6} \)th or \( \frac{1}{3} \)th of a line thick, tough, of a dun-gray or fawn colour (intermediate between Sienna-yellow and ochre-yellow, Syme), slightly translucent, and sinking in water. The attached or inner surface is flocculent and tomentose, and a shade lighter than the outer, which presents a sort of shag or velvet, consisting of very minute piles. This, when examined by a good lens at oblique light, appears to consist of an infinite number of very minute roundish bodies closely set, but separated by equally minute linear pits, and occasionally circular depressions. In the ileum it presents much the same characters; but the minute bodies of its shaggy surface are still larger and more distinct, and may be seen by the naked eye. In the windpipe, again, it is rather thinner and lighter coloured; and while its outer surface presents numerous minute pores, it is much smoother than in the alimentary canal, and entirely destitute of those minute bodies seen in the latter. It nowhere presents any appearance of fibres.
The mucous corion rests on a layer of filamentous tissue, firm and dense, and of a bluish-white colour, a character by which it is distinguished from the soft fawn-coloured mucous membrane. This submucous filamentous tissue is what is erroneously termed the nervous coat by Ruyssch, Albinius, and some of the older anatomists.
In certain parts the mucous corion is covered by a thin transparent membrane, named the epidermis or cuticle, which is most easily shown by boiling or scalding a portion of mucous membrane, and then peeling off with care the outer pellicle. This experiment succeeds best in the mucous membrane of the mouth and palate, in which, therefore, the existence of mucous epidermis cannot be doubted. The observations of Wepfer, Haller, and Nicholls, and especially of Bleuland (Observationes Anatomico-Medicae de Sua et Morboea Æsophagi Structura, Lug, Bat, 1785), are sufficient to prove its existence in the esophagus. Bichat admits that, though it may be demonstrated at the cutaneous junctions of the mucous surfaces, it cannot be recognised in the stomach, intestines, bladder, &c. From the numerous dissections of Home (Phil. Trans. 1807, 1810, 1813), it results that the mucous epidermis, both in the human subject and in most mammalia and birds, terminates abruptly at the cardiac orifice of the stomach. In ruminant animals the mucous epidermis is continued over the first two stomachs, but cannot be traced in the third and fourth. In the whale tribe, in which the stomach is also quadruple, the epidermis is confined to the first cavity. In birds of the grazing tribe, the mucous epidermis is continued over the gizzard, but terminates at the opening into the stomach. This conclusion as to the human subject is confirmed by Beclard, who further adds, that in the genito-urinary system it cannot be traced beyond the neck of the womb and that of the bladder.
In most mucous membranes are found minute oval or spheroidal bodies, slightly elevated, and presenting an orifice leading to a blind or shut cavity. As they are believed to secrete a fluid analogous to or identical with mucus, they are named mucous glands; and from their shape and situation they are also denominated follicles (folliculi) and cryptae. Though more or less abundant in all the mucous membranes, they have been most frequently examined in those of the alimentary canal, where they were first accurately described by Brunner and Peyer. (Glandula Peyeriana.) In this situation they are situate in the substance of the mucous corion. Their structure is simple. The orifice leads into a saccular cavity, with a smooth, uniform surface, which secretes the fluid which oozes from them. This membranous sac is lodged in a reddish-coloured, dense, anormal matter, which is probably filamentous tissue enveloping minute blood-vessels; but of the minute structure of which nothing is accurately known. In the state of health these bodies are so minute that it is very difficult to recognise them. I have seen them, nevertheless, in the tracheo-bronchial membrane by the eye and by a lens. When the membranes are inflamed they become larger and more distinct. In the bladder, the womb, the gall-bladder, and the seminal vesicles, they are not distinctly seen, and cannot be satisfactorily demonstrated. It is unnecessary, however, to follow the example of Bichat in trusting to analogy to prove their existence; for they are not necessary to the secretion of mucous fluid, as he seems to imagine. Those in the urethra, first well described by William Cowper, are distinct examples of follicles in the genito-urinary surface. The sinuosities (lacunae), first accurately described, if not discovered, by Morgagni (Adversaria Anatomica, iv. 8, 9, &c.), though not exactly the same in conformation and structure, seem to be very slightly different.
In certain regions of the mucous membranes, especially at their connections with the skin, are found minute conical eminences denominated papillæ. They are distinctly seen in the mucous membrane of the tongue, where they vary in size and shape, and in the body named clitoris. They are elevations belonging to the mucous corion, covered by epidermis, and they are liberally supplied by blood-vessels, the veins of which present an erectile arrangement, and with minute nervous filaments.
In the stomach, duodenum, and ileum, this membrane is collected into folds or plaits, which have received in the former situation the name of rugæ, or wrinkles; and in the latter the name of plica, or folds, and valvula commissurata, or wrinkled valves. In the vagina also are transverse rugæ, which in like manner are folds or duplicatures of its mucous membrane. Those of the esophagus, which have been described by Bleuland, are longitudinal. In the tracheo-bronchial membrane, and in the membranous and spongy portions of the urethra, we find them in the shape of minute plaits or wrinkles in the long direction of their respective tubes, but rarely of much length. The object of these folds, which are peculiar to the mucous membranes, appears to be to increase the extent of surface, and to allow the membrane to undergo considerable occasional distension. In certain points, where a communication is observed between the general mucous surface and the cavities or recesses of particular regions, anatomists, unable to demonstrate a mucous membrane, have inferred its existence as a continuation of the general surface. In the tympanal cavity, to which the Eustachian tube leads, the existence of a mucous or fibro-mucous membrane is rather presumed from analogy than proved by observation. We know that, where the biliary and pancreatic ducts enter the duodenum, and for a considerable space towards the liver, the interior appearance is that of a fine mucous surface provided with lacunae and villosities; but it is impossible to say at what point of the hepatic duct, or of the smaller canals of which it is formed, the mucous membrane terminates. The tracheal membrane, when traced to the bronchial divisions, presents no arrangement, either of papillae, piles, or villosities; and nothing is perceived except a smooth uniform surface, of a colour between gray, dun, and red or purple, which is moistened with a viscid semi-transparent fluid, and which is as like the peritoneum as the intestinal mucous membrane. Lastly, the situation where the existence of the mucous system, though believed, is most uncertain, is in the interior of the rena deferentia, where they take their origin from the rena efferentia of the testis. Regarding the organization of these tubes, no sensible evidence can be obtained, and whatever is stated concerning it is the result of analogical inference.
Though these membranes have been designated by the general name of mucous, the action of their surface is not in every situation the same. It is not easy to limit the signification of the term mucous; for this fluid varies in the nasal passages, in the trachea and bronchial membrane, in the oesophagus, stomach, and intestines, and in the urinary bladder and ureters. But it may be stated that many parts of the two mucous surfaces never in the healthy state secrete any modification of this animal matter; and in others the membrane is almost always moistened by a different fluid. The mucous or villous membrane of the eyelids is never in the healthy state occupied by mucus, but is uniformly moistened with tears; the membrane of the mouth and throat is moistened with saliva only; the urethra presents a peculiar viscid fluid, which seems to exude from many minute vessels opening along its surface, as in the lacunae, but which is widely different from mucus. All those parts, in short, which are not in perpetual, but only occasional, contact with foreign or secreted substances, seem to present no mucus in the healthy state; whereas the surfaces of the stomach, intestines, gall-bladder, and urinary bladder, are constantly covered with a quantity, more or less considerable, of this animal secretion.
The chemical properties of mucous membranes are completely unknown. The analysis of the fluid secreted by them has been executed by Fourcroy, Berzelius, and others, but is foreign to the subject of this article.
That the mucous membranes are liberally supplied with blood by vessels both large and numerous, is proved not only by the phenomena of injections, but by the red colour of which many of their divisions are the seat. This coloration, as well as the injectibility, is not indeed uniform; for in certain regions mucous surfaces are pale or light blue, in others their redness is considerable.
Thus, in those regions in which the mucous membranes coalesce with the periosteum, forming fibro-mucous membranes, e.g., in the facial sinuses, the tympanal cavity and the mastoid cells, the colour is pale blue, or approaching to light lilac. In the bladder, in the large intestines, in the excretory ducts in general, though pale, this colouring becomes more vivid. In the pulmonic mucous membrane it is slate-blue, verging to pale pink. In the stomach, duodenum, small intestines, and the vagina, it becomes still more marked. In the uterus it varies according to the period or the intervals of menstruation.
Examined in the gastro-enteric mucous membrane, in which they are most numerous, these vessels are found to consist of an extensive net-work of capillaries divided to an infinite degree of minuteness, mutually intersecting and spreading over the upper or outer surface of the mucous corion. This vascular net-work, though demonstrated by Ruysch, Albinus, Haller, and Bichat, has been beautifully represented in the delineations of Bleu land, who thinks he has traced their minute ramifications into the villi. These minute vessels are derived from larger ones, which creep through the submucous cellular tissue, and penetrate the mucous corion, the substance of which receives few or no vessels, to be finally distributed at its exterior surface.
The arrangement of the vessels which supply the mucous surfaces is peculiar. Penetrating, in the form of considerable trunks, between the folds of the serous membranes, they divide in the subserous cellular tissue into branches of considerable size; and here they form those numerous anastomotic communications which constitute the arches so distinctly seen in the ileum. From the convexity of these arches are sent off most of the small vessels, which are then fitted, after passing through the muscular layer and the submucous tissue, to enter the mucous corion.
The capillary terminations, then, of these arteries, and their corresponding veins, constitute the physical cause of the coloration of the mucous membranes. This coloration, however, is not at all times of the same intensity in the same membrane, and varies chiefly according to the state of the organ which the membrane covers. The coloration of the gastro-enteric mucous membrane undergoes, even within the limits of health, many variations. Thus, according to the absence or presence of such foreign substances as are taken at meals, the mucous membrane is pale, or presents various shades of redness. At the period of menstruation the uterine mucous membrane becomes red and injected. Pressure on any of the venous vessels renders the mucous membranes blue, purple, or livid, as is seen in proctitis, and more distinctly in asphyxia, in which all the mucous membranes assume a livid tint. (Bichat.) The varieties of red colour observed in the gastric mucous membrane by Dr Yellowly are to be ascribed partly to the latter cause, partly to the vascular redness which the presence of foreign bodies occasions. (Medico-Chirurg. Trans. vol. iv. p.371.) The pulmonary division of this membrane is of an ash-gray or dun colour, inclining to pale blue or light red. These colours vary, nevertheless, according to the facility or the difficulty with which the blood moves through the pulmonary capillary system. It is also freely supplied with blood-vessels derived chiefly from the bronchial arteries. These vessels, after accompanying the bronchial tubes and their successive subdivisions, divide into minute branches which penetrate the mucous corion, which here is white, dense, and fibrous, and after anastomosing with the capillaries of the pulmonary artery and veins, form a minute delicate net-work on the outer surface of the pulmonary mucous membrane. According to Reisscissen, to whom we are indebted for a careful examination of these vessels, a successful injection of them from the bronchial arteries renders the whole mucous membrane of the bronchi entirely red to the unassisted eye. (Uber den Bau der Lungen, u.s.w. Berlin, 1822.) The termination of arteries at the mucous surfaces has always occupied the attention of anatomists and physiologists; but it is not a matter of sensible demonstration. The thin serous or sero-mucous fluid with which they are moistened has led every author almost, and among the rest Haller and Bichat, to infer the existence of arteries with orifices, or what are termed exhalant vessels. It has been admitted, nevertheless, more on analogical than direct proofs. The injections of Bleuland, the only experiments, after those of Kawe Boerhaave, which tend to confirm the conclusion, require nevertheless to be repeated and varied.
That lymphatics are distributed to mucous membranes, is a point well established. Cruikshank saw the lymphatics proceeding from the pulmonic mucous membrane loaded with blood in persons and animals dying of haemoptoea. Their existence in the gastro-enteric mucous membrane has been long established.
The mucous surfaces are also freely supplied by nervous twigs and filaments, derived in general from the nerves of automatic life. It is a mistake, nevertheless, to ascribe to these filaments the sensibility and other properties of the mucous membranes, which possess intrinsically certain vital properties independently of the nervous filaments with which they are supplied; and the principal use of these filaments appears to be to regulate these properties, especially that of secretion.
The connection between the mucous membranes and the skin was first demonstrated by Bonn, who traces their mutual approximation and reciprocal transition into each other, and represents the former as an interior production of the latter, enveloping the internal as the skin incloses the external organs. This view has been adopted by Meckel and Beclard, to whom I refer for the proofs of its accuracy. I cannot conclude the subject, however, without observing that one of the most conclusive arguments in its favour is derived from the circumstances of the development of the intestinal canal during the first months of uterine life. The history of this curious process, which has been investigated by Wolff, Oken, and Meckel, shows that at this period the gastro-enteric mucous membrane, which is previously formed by the vitellar membrane of the ovum, and the allantois or vesical membrane, which afterwards forms the genito-urinary mucous surface, are in direct communication on the median line, and afterwards at the navel, with the skin or exterior integument.
Serous Membrane, Transparent Membrane. (Membrana Pellucida, M. Serosa.—Tissu Serieux.)
The pleura and peritoneum are the best examples of membranes, the tissue which has been named serous, from the fluid with which it is moistened, and which may be termed transparent or diaphanous as its distinctive character.
The distribution or mechanical arrangement of these membranes is peculiar, and though not well understood by anatomists, till Douglas, by his description of the peritoneum, rendered it clearer, may now be said, by the labours of Hunter, Carmichael Smyth, and Bichat, to be quite intelligible. In this, nevertheless, there are certain peculiarities which may perplex the beginner, and prevent him from obtaining at first a clear idea of the distribution and configuration of the pellucid membranes. Thus they have neither beginning nor termination; they have neither orifice nor egressient canal; and they are not continuous with any other membrane or texture.
Every serous membrane consists of a hollow sac everywhere closed, and to the cavity or interior surface of which there is no natural entrance; a circumstance from which they have been denominated shut sacs (sacce occlusi; sacs sans ouverture). In every serous membrane one part is inverted or inflected, or reflected, as is commonly said, within the other, so that the inner surface of the former part is applied with more or less accuracy to the inner or like surface of the latter. This mode of disposition has suggested the homely and trite, but not inappropriate comparison of a serous membrane to a night-cap, one half of which is folded or doubled within the other, so that while one half of the inner surface is applied to the remaining half, no communication exists between the inner and the outer surface. Every serous membrane, in short, is a single sac, one half of which is doubled within the other.
In every serous membrane the outer surface of the unreflected portion is applied over the walls of the region which the serous membrane lines, while the outer surface of the inflected portion is applied over the organ or organs contained in that region. From this arrangement it results that each organ covered by serous membrane is not contained in that membrane, but is on its exterior surface, and that of every organ so situate, one part at least, viz. that at which its vessels and nerves enter, is always uncovered. Thus the lungs are on the outer surface of the pleura; the heart is on the outside of the pericardium; the stomach, intestines, liver, spleen, and pancreas, are on the outside of the peritoneum; and the testicles are on the outside of the peridymis. In the same manner the lungs, though invested by pleura before and behind, at their apex and their base, are uncovered at their roots, or the points where the bronchial tubes and great blood-vessels enter their substance; the heart is uncovered by pericardium at the upper part of the auricular cavities; and the intestinal canal is uncovered along the whole of that longitudinal but tortuous line by which the mesentery is attached, and at which its proper vessels and nerves are transmitted.
To comprehend more distinctly the arrangement of the pellucid membranes, it is expedient, by an effort of abstraction, to trace the course of any one of them, having previously thrown out of the question the means by which their interior free surface is exposed. In this mental process it is requisite to remember that there is no initial point save what is arbitrarily made. If, for example, the course of the pleura be traced, the membrane presents no natural boundary from which the anatomist is to commence his demonstration; and he must fix artificially on any point which he finds most convenient for the purpose. Commencing with this understanding, from the circumference of the spot termed root of the lungs, the membrane may be traced first along the internal surface of the chest formed by the ribs and intercostal muscles, forwards to the sternum, upwards to the first rib and apex of the thoracic cavity, downwards to the diaphragmatic insertions, and over the surface of that muscle, and the outer surface of the pericardium again to the circumference of the root or connection of the lungs. From this point again it may be traced over the surface and between the lobes of these organs, both of which, as already stated, are thus situate on the outside of the pleura. The course first described is that of the unreflected or exterior division of the pleura. The second, or that over the organ covered, is the course of the inflected or doubled portion of the membrane, which is thus necessarily smaller, and less extensive, than the former.
The arrangement thus sketched, which may be easily shown to be applicable to all the serous membranes, demonstrates their twofold character of lining the walls of a cavity and covering the organs contained. From an idea of this property, the old anatomists applied to them the epithet of membranae succingentes.
In tracing the course of the serous membranes, the anatomist observes that they present productions which float with more or less freedom in the cavity formed by the free surface, and which may be generally shown to consist of two folds of the single membrane produced beyond the inclosed organ, but still maintaining the unity of the membrane. Of these prolongations, the most distinct examples are the epiploa and the appendices epiploicae of the peritoneum. Less manifest instances are the adipose folds of the pleura near the mediastinum, and the bladder-like appearance at the base of the heart, within the pericardium. The synovial fringes in the interior of the synovial membranes, which belong to a subsequent head, are nevertheless of the same general character. Between the folds of these productions there is invariably more or less adipose substance, which indeed is observed in some quantity in various parts of the filamentous tissue on the outer surface of the serous membranes in general.
Every serous membrane I have above represented as a hollow sac everywhere continuous, and the outer surface of which has no communication with the inner. To this character the only exception is the peritoneum in the female, which is perforated at two points, corresponding to the upper extremity or orifice of the Fallopian or oviducts. This has been already mentioned as the only spot at which the mucous and serous surfaces communicate directly with each other.
Every serous membrane consists of a thin, colourless, transparent web or pellicle, through which the tissue of the subjacent organ or parts may be easily recognised; and every serous membrane presents two surfaces, an attached or adherent, and a free or unadherent.
The attached surface, which is also termed its outer one, is that by which it is connected to the tissue or organ which it covers; it is somewhat irregular, flocculent or tomentum, and is evidently connected by fine filamentous tissue. The degree of attachment is very variable in different membranes, and in different points of the same membrane. In general, serous membranes adhere much less firmly to the walls of cavities than to the surface of the contained organs. Thus, the abdominal peritoneum and the costal pleura are more easily removed than the intestinal peritoneum and the pulmonic pleura. The peritoneum adheres feebly to the bladder, to the liver, and to the pancreas—more intimately to the different regions of the intestinal tube, and seems to be almost identified with the substance of the female organs of generation. From the interior of the capsular pericardium, and from the vaginal coat, it is almost impossible to detach the serous pellicle. The former, however, is peculiar in having between the serous surface and the fibrous membrane no filamentous tissue, upon the abundance or deficiency of which the degree of adhesion depends.
The free or unadherent or inner surface is very smooth, polished, and uniform; moistened with a watery fluid, from which it derives its shining appearance; and destitute of fibres or any other trace of organic structure.
From this smooth, polished aspect, which is a peculiar attribute of the free surface of serous membrane, all the organs covered by it derive their glistening appearance. Thus the exterior surface of the lungs derives its appearance from the pleura, the heart from the pericardium, and the liver and intestinal canal from the peritoneum. A successful injection of size or turpentine, coloured with vermilion, brings into view so many capillary blood-vessels in this membrane, that it might be supposed at first sight to consist entirely of minute arteries and veins. Further, by proper management, lymphatics may be injected in it with quicksilver to a degree equally minute and delicate. From these experiments, therefore, it may be concluded that serous membrane is chiefly composed of minute arteries and veins conveying colourless fluids, and of vessels connected with the general trunks of the lymphatic system. Whether it contains anything else but vessels of this kind, or has a proper substance or tissue, remains to be ascertained. Though nerves are often seen passing along their outer or attached surface to the neighbouring tissues, none have hitherto been traced either into the pleura or peritoneum.
By most of the older anatomists, and among others by Haller, serous membrane is considered as of the nature of filamentous tissue or cellular membrane, more or less closely condensed (tela cellulosa stipata); and this view is adopted and maintained by Bordeu, Bichat, Meckel, and Beclard, the last of whom, however, thinks they partake of ligamentous characters. Macerated, they become soft, thick, and pulpy; and are finally resolved into flocculent filamentous matter. In the course of decomposition in the dead subject they first lose their glistening aspect, then become covered by a foul, dirty coating of viscid matter, which appears to exude from their surface; and eventually they are dissolved into shreds. Immersion in boiling water renders them thick, firm, and somewhat crisp. When dried they become thin, clear, and transparent, and, if preserved from humidity or the attacks of animals, may remain long unchanged. The experiments of Hatchett, Fourcroy, and Vauquelin, show that they contain gelatine and a little albumen; but no precise information on their chemical composition has yet been given.
The principal character of the serous membranes is that of isolating the organs which they cover, and to the structure of which they are adventitious, and forming shut cavities, in which there is incessant exhalation and absorption. In some instances they evidently contribute to facilitate the mutual motions of contiguous and corresponding surfaces. From their free surfaces is secreted a fluid containing a small portion of albumen (Hewson, Experimental Inquiries, vol. ii. chap. vii.; Bostock, Nicholson's Journal, vol. xiv. p. 147; and Medico-Chirurgical Transactions, vol. iv.), which is greatly augmented during the state of disease.
The mode of development of the pellucid membranes is not well ascertained. The investigations regarding organogenesis by Oken, Meckel, and Tiedemann, disclose facts which induce Meckel to hazard the opinion that some of them are not at all times shut sacs. I doubt, however, whether the fact which he adduces for this purpose implies the open condition of the pericardium and the peritoneum. In the case of the former the development of the heart proceeds from the basis generally, without affecting the integrity of the investing membrane. In the case of the latter there is more reason to believe that, at the navel, at least, the peritoneum is either open, or is continuous with the vitellar membrane.
In the fetus the serous membranes are so thin, that General they are much more transparent than in the adult. In Anatomy, small animals also, they are more transparent than in large, and in cold-blooded animals than in the mammiferous. Of some also the disposition varies at different periods. Thus the descent of the testicle,—a process which has been well explained by Albinius, Haller, Wrissberg, and Langenbeck,—is attended with a remarkable change in the arrangement of that portion of peritoneum which the gland impels before it.
Synovial Membrane. (Membrana Synovialis; Bursae Mucosae.)
Bichat enumerates several circumstances in which he conceives that serous and synovial membranes differ from each other. Gordon, who doubts how far the distinctions are well founded as the basis of anatomical arrangement, admits, however, the following peculiarities.
Synovial membrane resembles serous membrane in being a thin, transparent substance, having one smooth free surface turned towards certain cavities of the body, and another connected by delicate cellular tissue to the sides of these cavities, or to the parts contained in them. But it differs from serous membrane in the following circumstances. 1st, It possesses little vascularity in the healthy state; no blood-vessels are almost ever seen in it after death, nor can they be made to receive the finest injection. 2d, Its lymphatics are quite incapable of demonstration. 3d, Very delicate fibres, like those of cellular substance, or like the finest filaments of tendon, are distinctly seen in it after slight maceration. 4th, It is considerably less strong than serous membrane. On these grounds, therefore, synovial membrane is to be anatomically distinguished from serous membrane.
The synovial membrane, as described above, is found not only in each of the movable articulations, but in those sheaths in which tendons are lodged, and in which they undergo considerable extent of motion, and in certain situations in the subcutaneous filamentous tissue.
The distribution of the synovial membranes is much the same in all these situations. They are known to line the ligamentous apparatus of each joint, capsular and funicular; and they are also continued over the cartilaginous extremities of the bones of which the articulation consists. This continuation, which was originally maintained by Nesbitt, Bonn, and William Hunter, and was demonstrated by various facts by Bichat, has been lately questioned by Gordon and Magendie, the former of whom especially thinks it unsusceptible of anatomical proof. The cartilaginous synovial membrane is certainly not so easily demonstrable as the capsular, for the same reason which I have already assigned regarding the difficulty of isolating the capsular pericardium, the ovarian peritoneum, and the serous covering of the tunica albuginea,—the want of filamentous tissue.
The presence of synovial membrane in the articular cartilages is nevertheless established by sundry facts. 1st, General anatomy. If a portion of articular cartilage be divided obliquely, and examined by a good glass, it is not difficult to recognise at one extremity of the section a thin pellicle, differing widely in aspect, colour, and structure, from the bluish-white appearance of the cartilage. 2d, If the free surface of the cartilage be scraped gently, it is possible to detach thin shavings, which are also distinct from cartilage in their appearance. 3d, The free surface of the cartilage is totally different from the attached surface, or from a section of its substance, and derives its peculiar smooth polished appearance from a very thin transparent pellicle uniformly spread over it. 4th, If articular cartilage be immersed in boiling water, this thin pellicle becomes opaque, while the cartilage is little changed. 5th, Immersion in nitric or muriatic acid, which detaches the cartilage from the bone, gives this surface a cracked appearance, which is not seen in the attached surface, and which is probably to be ascribed to irregular contraction of two different animal substances. 6th, The existence of this cartilaginous synovial membrane is demonstrated by the morbid process with which the tissue is liable to be affected. On the whole, therefore, little doubt can be entertained that the representation of their course, as given originally by Nesbitt, Bonn, and Hunter, is well founded.
The same views may be applied to the synovial linings of the tendinous sheaths, which are equally to be regarded as shut sacs.
Attached to the free surface of each synovial membrane is a peculiar fringe-like substance, which was long supposed to be an apparatus of glands (glands of Havers) for secreting synovial fluid. It is now known that these fringes are merely puckered folds of synovial membrane, and that, although synovia is abundantly secreted by them, this depends merely on the great extent of surface which is the necessary consequence of their puckered arrangement. This arrangement is easily demonstrated by immersing an articulation containing the fringed processes in clear water, when they are unfolded and made to float, and show their connections, figure, and terminations. They are analogous to the free processes of serous membranes, and like them are double, and contain adipose matter.
The synovial sheaths (bursae mucosae) are very numerous, and are generally found in every tendon which is exposed to frequent or extensive motion.
Though the fluid prepared by these membranes has been examined by Margueron, Fourcroy, John Davy, Orfila, and other chemists, it cannot be said that its chemical composition is accurately determined. It is said to contain water, albumen, incongelable matter regarded as mucilaginous gelatine, a ropy matter, and salts of soda, lime, and some uric acid. On the presence of the incongelable gelatine depends its utility in diminishing friction in the finer kinds of metallic machinery employed in watches and chronometers.
END OF VOLUME SECOND.