Is that branch of anatomy which considers the secondary objects, or the bodies of other animals; serving for the more accurate distinctions of several parts, and supplying the defect of human subjects.

It is otherwise called the anatomy of brutes, and sometimes zootomy; and stands in contradiction to human anatomy, or that branch of the art which considers the human body the primary object of anatomy. See Anatomy.

INTRODUCTION.

The principal advantages of comparative anatomy are the following: First, it furnishes us with a sufficient knowledge of the different parts of animals, to prevent our being imposed upon by those authors who have delineated and described several parts from brutes as belonging to the human body. Secondly, it helps us to understand several passages in the ancient writers in medicine, who have taken many of their descriptions from brutes and reasoned from them. The third and great use we reap from this science, is the light it casts on several functions in the human economy, about which there have been so many disputes among anatomists.

In this view it is altogether needless to insist on those parts whose use is usually understood when once their structure is unravelled: Thus, for instance, if we be acquainted with the action of the muscles in general, it will not be difficult to determine the use of any particular muscle whose origin and insertion is known, if we at the same time consider the various connections of the bones to which it is fixed, and the different degree of mobility they have with respect to each other. In the same manner, if we know the use of the nerves in general, we can easily assign the use of those nerves which are distributed to any particular part. There is then no occasion for a complete osteology, myology, &c. of the several animals we shall treat of, nor need we trouble ourselves about the structure of any of the parts, unless when it serves to illustrate some of the fore-mentioned purposes.

That the first use we proposed from examining the structure of the parts in brutes is real and of consequence, is evident from looking into the works of some of the earliest and greatest masters of anatomy, who for want of human subjects have often borrowed their descriptions from other animals. The great Vesalius, although he justly reproves Galen for this fault, is guilty of the same himself, as is plain from his delineations of the kidneys, uterus, the muscles of the eye, and some other parts. Nor is antiquity only to be charged with this, since in Willis's Anatomia Cerebri (the plates of which were revised by that accurate anatomist Dr. Lower) there are several of the pictures taken from different brutes, especially the dog, besides those he owns to be such. We shall give several examples of the second use in the sequel of the work.

The animal kingdom, as well as the vegetable, contains the most surprising variety, and the deficient unity and uniformity observable in nature are almost imperceptible. The bat and flying-squirrel, though quadrupeds, have wings to buoy themselves up in the air. Some birds inhabit the waters; and there are fishes that have wings, and are not strangers to the airy regions: the amphibious animals blend the terrestrial and aquatic together.

As there is then such a vast variety, it is not only needless, but impossible, to consider all of them particularly. We shall take only some of the most remarkable genera; and hope, from what will be said of them, any of the intermediate degrees may be understood.

In treating of quadrupeds, we shall divide them into Division of the carnivorous, i.e., those that feed indifferently on animal and vegetable substances, and granivorous: as quadrupeds, volatiles, fishes, ruminants, &c. The fowls we shall also divide into those that feed on grain, and those that feed on flesh. The distinction we shall make in treating of fishes, shall be of those that have lungs, and those that have them not. The first indeed are with difficulty procured, and at the same time differ very little from quadrupeds. The structure of insects and worms is so very minute, that little assistance for the ends proposed by the present subject has been expected from their anatomical investigation. As they constitute, however, one of the great classes into which animals are divided, and as every advance in knowledge, with respect to the structure of any one animal, must either directly or indirectly cast some light on the structure of some part of every other, we have thought proper to add a few particulars concerning them.

In inquiring into the structure of different animals, we ought to be previously acquainted with the form of their body, manner of life, kind of food; or, in short, with their natural history; which will lead us to account for the reason of their different structure, and hence explain the actions of the human body. Of all these particulars a detail will be found under the titles of the different subjects in their alphabetical order. CHAP. I. Anatomy of Quadrupeds.

SECT. I. General Observations.

A question has been started by some fanciful philosophers, "Whether man is naturally a biped or a quadruped?" and much ingenuity has been employed to establish the latter opinion. But it is presumed that few of their readers have been made converts to such an opinion, and that not many of ours will require much argument to persuade them of their erect definition. It may therefore suffice to observe, that this erect position is best adapted to the conformation of the human head, and the ponderous quantity of human brains—that the articulation of the os occipitis with the first vertebrae of the neck, is differently constructed from that of quadrupeds, with the obvious design that man should be able to move his head in every direction with the greatest facility—that the human species (and also monkeys) are destitute of that strong ligament or tendinous aponeurosis, vulgarly called pannus, which quadrupeds possess (as a kind of stay-tape), to prevent the head from sinking to the earth; to which, from its natural position, it must be very prone—and that our eyes and ears are, fortunately, not placed as those of the quadrupeds. The axis of the human eye is nearly perpendicular with a vertical section of the head; whereas, in the brute creation (the larger ape excepted), the position of the eyes forms an acute angle—man has also furnished other animals with a suspensorium oculi, a muscle which the erect attitude renders needless, though highly necessary in the prone; consequently, whoever tries the experiment will find that, in the inclined direction, both his eyes and his ears are in the most unfavourable situation possible for quick hearing or extensive vision. In fine, the shape, breadth, strength of the vertebrae of the back and loins, are all coincident with the erect attitude of the trunk.

All quadrupeds have a covering of hair, wool, &c., to defend them from the injuries of the weather, which varies in thickness according to the season of the year and difference of the climate: thus in Russia and the northern countries, the furs are very thick and warm, while the little Spanish lap-dogs, and Barbary cows, have little or no hair at all.

The cutis and cuticula in quadrupeds are disposed much in the same way as the human, only more elastic; immediately under this, there is a very thin cutaneous muscular substance called panniculus carnosus, which is common to all quadrupeds, the porcine kind excepted; this principally covers the trunk, serving to shrivel the skin, in order to drive off insects, their tails and heads not being sufficient for this purpose, while their extremities are employed in their support and progression.

It has probably been from observing some muscles of the human body, such as the platysma myoides, cremafter, and frontales, and the collapsed tunica cellulosa of emaciated subjects, to resemble this thin muscle, that some of the older anatomists reckoned such a panniculus among the common teguments of the human body. This Carolus Stephanus has well observed.

Most part of quadrupeds want clavicles, whereby their anterior extremities fall upon their chest, so as to make their thorax proportionally narrower than the human. This small distance of their anterior extremities is very necessary for their uniform progression: apes indeed and squirrels have clavicles to allow them a more full use of their extremities in climbing; but when they walk on all-fours, they move but indifferently.

SECT. II. Of the Orang Outang.

While some philosophers, as above noticed, have endeavoured to level man to the rank of quadrupeds, others have attempted to elevate certain of the brute creation to the same class with their reputed lords. The orang outang is ranged by Linnaeus as congeners with man, (See Homo); and some theorists have even considered him as the original stock of the human race, pretending that he has been the man of the woods for many ages before gardens were ever thought of. His claims to humanity are founded on his being able to walk upright occasionally, being furnished with a competent share of muscles requisite for the purpose. The form of his heart, lungs, breast, brains, intestines, are similar to those of men; the cæcum has also its appendix vermiformis; he can sit upright with great ease; shows more design in his plans than his associates in the forests; and can handle a stick on occasion with tolerable dexterity. His disqualifications are the following: The position of the foramen magnum occipitis, which is farther backward than in the human species, and the sockets of his lower jaw, made to receive the dentes incisores of the upper, indicate his relationship to the monkey breed. He has also thirteen ribs on each side; his arms, feet, and toes, are much longer than those of the human species, &c. and although his foot does not so closely resemble a hand as that of the ape, yet the pollex pedis, or the great toe, is placed at a greater distance from the other toes, which gives it the appearance and uses of a thumb. These differences indicate, that, although the orang can occasionally act the biped, yet he is much better qualified to walk on his fore-feet, and to climb trees, than the generality of the modern race of men. But an objection to his claims, still weightier than any of the differences stated above, arises from his want of speech. For there is no nation of men, however savage, that is destitute of speech; though individuals, secluded from society, may in time lose the faculty. No instances are known in which a company of ten or twelve men have been without a language; but upwards of thirty of the orang species have been found in a herd, without showing the slightest traces of this faculty. It has been suggested by Rousseau, that they may have lost the power from their neglect of using it; but it is very singular that they alone should lose this power, and not that race of men to whom they are supposed to be so nearly related. This point, however, has been completely decided by the discoveries of professor Camper; who in a paper in the Philosophical Transactions† has demonstrated, by an anatomical dissection of the organ of the voice, that articulation is rendered impossible in these animals in consequence of the structure of that organ. From the nature and situation of those parts in the orang (as well as in the ape and in the monkey) he has proved, that no modulation of the voice resembling human speech can be produced in these creatures; because the air, passing through the rima glottidis, is immediately lost in two ventricles or hollow bags in the neck (which are sometimes united into one), with which all these animals are furnished, and which have a communication with the mouth through the said rima or slit; so that the air must return from thence, without any force or melody, within the throat and mouth of these creatures.

Sect. III. The Anatomy of a Dog.

We may first observe of this animal, as indeed of most quadrupeds, that its legs are much shorter in proportion to its trunk than in man, the length of whose steps depends entirely on the length of his inferior extremities; however, to balance this, the trunk of the animal is proportionally longer and smaller, its spine more flexible, by which he is able at each step to bring his posterior extremities nearer to his anterior. His common teguments are much akin to those of other quadrupeds, only they allow little or no passage for sweat; but when he is over-heated, the superfluous matter finds an exit by the salivary glands, for he lolls out his tongue and slavers plentifully. We are not, however, to suppose, that because a dog does not sweat, he has no infallible perspiration. That a dog perspires is evident, because one of these animals can trace another by the scent of his footsteps; which could not happen if a large quantity of perspirable matter was not constantly going off.

The pyramidal muscles are wanting, to supply which the rectus is inserted fleshy into the os pubis.

The omentum reaches down to the os pubis, which considering the posture of the animal we will find to be a wise provision, since its use is to separate an oily liquor for lubricating the guts and facilitating their peristaltic motion; so in our erect posture the natural gravity of the oil will determine it downward, but in the horizontal position of these creatures, if all the intestines were not covered, there would be no favourable derivation of the fluid to the guts lying in the posterior part of the abdomen, which is the highest; and besides, had the omentum reached much farther down in us, it would not only have supplied too great a quantity of oil to the lower part of the abdomen, but we would have been in continual danger of herniae; and even at present the omentum frequently passes down with some of the other viscera, and forms part of these tumors. To these, however, the dog is not subject, as his viscera do not press so much on the rings of the abdominal muscles, and besides are prevented from passing through by a pendulous flap of fat, mentioned no 35. The inferior and anterior lamella of the omentum is fixed to the spleen, fundus of the stomach, pylorus, liver, &c. in the same way as the human; but the superior having no colon to pass over, goes directly to the back-bone. This serves to explain the formation of the small omentum in the human body; which is nothing but the large omentum, having lost its fat, passing over the stomach and colon, where it reassumes its pinguedo, proceeds, and is firmly attached to the liver, spine, &c. The trise of fat are pretty regularly disposed through it, accompanying the distribution of the blood-vessels to guard them from the pressure of the superincumbent viscera.

This animal's stomach, though pretty much resembling the human in its shape, is somewhat differently situated. It lies more longitudinal, as indeed all the other viscera do, to accommodate themselves to the shape of the cavity in which they are contained; that is, its inferior orifice is much farther down with respect to the superior than the human: by this means the dog's food has an easier passage into the duodenum. Again, the fundus of the human stomach, when distended, stands almost directly forwards, which is occasioned by the little omentum tying it so close down to the back-bone, &c. at its two orifices; but it not being fixed in that manner in the dog, the fundus remains always posterior: this also answers very well the shape of the different cavities, the distance between the cardia and fundus being greater than that between the two sides. It seems to be much larger in proportion to the bulk of the animal than the human, that it might contain a greater quantity of food at once; which was very necessary, since this animal cannot at any time get its sustenance as men do. The turbillion is not so large, nor is there any coaction forming the antrum Willisi, as in the stomach of man. It is considerably thicker and more muscular than ours, for breaking the cohesion of their food, which they swallow without sufficient chewing. Hence it is evident the force of the stomach is not so great as some would have it, nor its contraction so violent; otherwise that of dogs would be undoubtedly wounded by the sharp bones, &c. they always take down; for the contraction here is still greater than in the human stomach, which is much thinner. The rugae of the tunica villosa are neither so large, nor situated transversely, as in the human, but go from one orifice to the other: the reason of which difference is, perhaps, that they might be in less danger of being hurt by the hard substances this creature frequently feeds upon; and for the same reason there is not the like coaction at their pylorus.

The intestines of this animal are proportionally much shorter than ours; for the food which these creatures mostly use, soon dissolves, and then putrefies; on which account there was no occasion for a long tract of intestines, but on the contrary that it should be quickly thrown out of the body. The same is to be observed of all the carnivorous animals. The muscular coat of the intestines is also thicker and stronger than the human, to protrude the contents quickly and accurately.

The valvulae conniventes are less numerous, and in a longitudinal direction; and the whole tract of the alimentary canal is covered with a slime, which lubricates the intestines, saves them from the acrimony of the excrementitious part, and facilitates its passage.

The duodenum differs considerably in its situation from the human. For in man it first mounts from the pylorus upwards, backwards, and to the right-side; then passes down by the gall-bladder; and, marching over the right kidney and superior part of the psoas muscles, makes a curvature upwards; and passes over the back-bone and vena cava inferior, to the left hypochondrium, where it gets through the omentum, mesentery, and mesocolon, to commence the jejunum, being firmly tied down all the way, the biliary and pancreatic ducts entering at its most depending part: Whereas, in the dog, the duodenum is fixed at the pylorus to the concave concave surface of the liver, and hangs loose and pendulous with the mesentery backwards into the cavity of the abdomen; then turning up again, is fixed to the back bone, where it ends in the jejunum; the bile and pancreatic juice are poured into it at the most depending part. Therefore the same intention seems to have been had in view in the formation of this part in both, viz. the giving the chyle, after the liquors of the liver and pancreas are poured into it, a disadvantageous course, that so it might be the more intimately blended with the humours before its entry into the jejunum, where the lacteals are very numerous: And thus, by reason of their different posture, the same design (tho' by a very different order of the parts) is brought about in both.

The other small guts are much the same with ours, only shorter. The great guts are also shorter and less spacious than in the human body; and we take it for a general rule, that all animals that live on vegetable food, have not only their small guts considerably longer, but also their great guts more capacious, than such creatures as feed on other animals. Hence man, from this form of his intestines, and that of the teeth, seems to have been originally designed for feeding on vegetables chiefly; and fill the most of his food, and all his drink, is of that class.

The reason of this difference seems to be, that as animal food is not only much more easily reduced into chyle, but also more prone to putrefaction, too long a remora of the juices might occasion the worst consequences. So it was necessary that their receptacles should not be too capacious; but on the contrary, being short and narrow, might conduce to the seafarable discharge of their contents. Whereas vegetable food being more difficultly dissolved and converted into an animal nature, there was a necessity for such creatures as fed on it to be provided with a long intestinal canal, that this food in its passage might be considerably retarded, and have time to change its indoles into one more agreeable to our nature. Besides which there is another advantage which accrues to man in particular, from having his great guts very capacious: for as he is a rational being, and mostly employed in the functions of social life, it would have been very inconvenient as well as unbecoming for him to be too frequently employed in such ignoble exercises; so that, having this large reservoir for his faeces alvine, he can retain them for a considerable time without any trouble.

The appendix vermiformis justly enough deserves the name of an intestinum sacum in this subject, though in the human body it does not; and it has probably been from the largeness of this part in this and some other animals, that the oldest anatomists came to reckon that small appendicle in man as one of the great guts. On its internal surface we observe a great number of mucous glands. As these throw out slime, their principal office would seem to be the procuring a sufficient quantity of that matter for the purposes above mentioned. Still, however, there seems to be some unknown use for this organ in other animals; for the appendicula vermiformis in them is either of great size or of great length. In a rat, it is rather larger than the stomach; in others, as swine, and some of the animals which live on vegetables, it has long convolutions, so that the food must be lodged in it for a long time. Thus, probably, some change takes place in the food, which requires a considerable time to effectuate, and, though unknown to us, may answer very useful purposes to the animal.

The colon has no longitudinal ligaments; and consequently this gut is not purred up into different bags or cells as the human; nor does this intestine make any circular turn round the abdomen; but passes directly across it to the top of the os sacrum, where it gets the name of rectum.

At the extremity of the intestinum rectum, or verge of the anus, there are found two bags or pouches, which contain a most abominable fetid mucus of a yellow colour, for which we know no use, unless it serves to lubricate the strained extremity of the rectum, and defend it against the asperity of the faeces, or to separate some liquor that might otherwise prove hurtful to their bodies. There is nothing analogous to those sacs in the human subject, unless we reckon the mucilaginous glands that are found most frequent and largest about the lower part of the rectum.

The mesentery is considerably longer than in the human body; that, in his horizontal situation, the intestines may rest securely on the soft cushion of the abdominal muscles. The fat is here disposed in the same way, and for the same reason, as in the omentum. The interstices between the fat are filled with a fine membrane. Instead of a great number of glandular vasa to be found in the human mesentery, we find Pancreas; the glands few in number, and those are closely connected together; or there is only one large gland to be observed in the middle of the mesentery of a dog, which, from its imagined resemblance to the pancreas and the name of its discoverers, is called pancreas Adelphi; but the resemblance, if there is any, depends chiefly on the connection, the structure being entirely different. The reason why this in man is as it were subdivided into many smaller ones, may possibly be, that as the guts of a human body are proportionally much longer than those of this creature, it would have been inconvenient to have gathered all the lactea primi generis into one place; whereas, by collecting a few of these vessels into a neighbouring gland, the same effect is procured much more easily. Whether the food in this animal needs less preparation in its passage through these glands, is a matter very much unknown to us; though it is certain that some changes really do take place.

The pancreas in man lies across the abdomen, tied down by the peritoneum; but the capacity of this creature's abdomen not allowing of that situation, it is disposed more longitudinally, being tied to the duodenum, which it accompanies for some way. Its duct enters the duodenum about an inch and a half below the ductus communis.

The spleen of this animal differs from ours very much, both in figure and situation. It is much more oblong and thin, and lies more according to the length of the abdomen, like the pancreas. Though the spleen of this creature is not firmly tied to the diaphragm (which was necessary in our erect posture to hinder it from falling downwards), yet by the animal's prone position,

The human liver has no fissures or divisions, unless you please to reckon that small one betwixt the two pulps, where the large vessels enter: Whereas in a dog, and all other creatures that have a large flexion in their spine, as lions, leopards, cats, &c., the liver and lungs are divided into a great many lobes by deep sections, reaching the large blood-vessels, which in great motions of the back-bone may easily shuffle over one another; and so are in much less danger of being torn or bruised, than if they were formed of one entire piece, as we really see it is in horses, cows, and such creatures as have their back-bone stiff and immovable. There is here no ligamentum latum connecting the liver to the diaphragm, which in our situation was necessary to keep the viscus in its place: Whereas in this creature, it naturally gravitates forwards, and by the horizontal position of the animal is in no danger of prefling against the vena cava; the preventing of which is one use generally assigned to this ligament in man. Had the liver of the dog been thus connected to the diaphragm, the respiration must necessarily have suffered; for, as we shall see afterwards, this muscle is here moveable at the centre as well as at the sides: But in man the liver is fixed to the diaphragm, mostly at its tendinous part; that is, where the pericardium is fixed to it on the other side; so that it is in no danger of impeding the respiration, being suspended by the mediastinum and bones of the thorax. In consequence of this viscus being divided into so many lobes, it follows, that the hepatic ducts cannot possibly join into one common trunk till they are quite out of the substance of the liver; because a branch comes out from every lobe of the liver; all of which, by their union, form the hepatic duct: whence we are led to conclude, that the hepato-cystic ducts, mentioned by former authors, do not exist. The gall-bladder itself is wanting in several animals, such as the deer, the horse, the ass, &c.; but in place of it, in such animals, the hepatic duct, at its beginning, is widened into a reservoir of considerable size, which may answer the same purpose in them that the gall-bladder does in others.

We come next, after having examined the chylopoietic viscera, to discourse of those organs that serve for the secretion and excretion of urine. And first of the kidneys: Which in this animal are situated much in the same way as in the human subject; but have no fat on their inferior surface, where they face the abdomen, and are of a more globular form than the human. The reason of these differences will easily appear, if you compare their situation and posture in this animal with those in a man who walks erect. They are placed in this subject in the inferior part of the body, so are not subject to the pressure of the viscera, which seems to be the principal cause of the fatness of those organs in us, and perhaps may likewise be the cause of our being more subject to the stone than other animals. Hence there is no need of any cellular substance to ward off this pressure where there would necessarily be fat collected; but the superior part of their kindneys is pretty well covered with fat, lest they should suffer any compression from the action of the ribs and spine.

In the internal structure there is still a more considerable difference: For the papilla do not here send out fipple the several tubuli uriniferi; but being all united, they hang down in form of a loose pendulous flap in the middle of the pelvis, and form a kind of septum medium; so that a dog has a pelvis formed within the substance of the kidney. The only thing that is properly analogous to a pelvis in man is that sac or dilatation of the ureters formed at the union of the ductus uriniferi. The external part of the kidney of a dog somewhat resembles one of the lobes of the kidney of a human fetus: but in a human adult the appearance is very different; because, in man, from the continual pressure of the surrounding viscera, the lobes, which in the fetus are quite distinct and separated, concrete, but the original cortical substance is still preserved in the internal parts of the kidney. The reason of these particularities may probably be, that the liquors of this animal, as of all those of the carnivorous kind, being much more acid than those that live on vegetable food, its urine must incline much to an alkaline state, as indeed the smell and taste of that liquor in dogs, cats, leopards, &c., evidently show, being fetid and pungent, and therefore not convenient to be long retained in the body. For this end it was proper that the secreting organs should have as little impediment as possible by pressure, &c., in performing their functions; and for that design, the mechanism of their kidneys seems to be excellently adapted: We have most elegant pictures in Eustachius of the kidneys of brutes, delineated as such, with a view to show Vesalius's error in painting and describing them for the human.

The glandulae or capsulae atrabiliaria are thicker and rounder than the human, for the same reason as the trabiliary kidneys.

The ureters are more muscular than the human, because of the unfavourable passage the urine has through them; they enter the bladder near its fundus.

The bladder of urine differs considerably from the vesica urinaria; and first in its form, which is pretty much maria pyramidalis or pyriform. This shape of the dog's bladder is likewise common to all quadrupeds, except the ape and those of an erect posture. In man it is by no means pyriform, but has a large sac at its posterior and inferior part: this form depends entirely on the urine gravitating in our erect posture to its bottom, which it will endeavour to protrude; but as it cannot yield before, being contiguous to the os pubis, it will naturally stretch out where there is the least resistance, that is, at the posterior and lateral parts; and were it not for this sac, we could not so readily come at the bladder to extract the stone either by the lesser or lateral operation of lithotomy. Most anatomists have delineated this wrong: so much, that I know of none who have justly painted it, excepting Mr Cowper in his Myologia, and Mr Butty. It has certainly been, from observing it in brutes and young children, that they have been led into this mistake. The same cause, viz., the gravity of the urine, makes the bladder of a different form in brutes: In their horizontal position the cervix, from which the urethra is continued, is higher than its fundus; the urine must therefore...

Chap. I.

Of Quadrupeds.

The rabies canina cannot with any probability be ascribed to it. As to want of water, he observes that the disease often originates among dogs that are plentifully supplied with that element, while others long deprived of it have remained perfectly free. In short, Dr Heysham totally denies, not only the efficacy of the caules commonly assigned for the rabies canina, but the nature of the distemper itself; and conjectures that the cause of it is not a putrefaction but an acidity of the fluids.

Their spermatic vessels are within the peritoneum, which is spread over them, and from which they have a membrane like a menstery, so hang loose and pendulous in the abdomen; whereas, in us, they are contained in the cellular part of the peritoneum, which is tenely stretched over them. At their passage out of the lower belly, there appears a plain perforation, or false holes; hence the adult quadruped, in this respect, resembles the human fetus. And from observing this hernia or rupture among authors. This opening, which leads down to the testicle, is of no disadvantage to them, but evidently would have been to us; for from the weight of our viscera, and our continually gravitating upon these holes, we must have perpetually laboured under enteroceles. This they are in no hazard of, fine in them this passage is at the highest part of their belly, and, in their horizontal posture, the viscera cannot bear upon it: And, to prevent even the smallest hazard, there is a loose pendulous seminal flap of fat; which serves two uses, as it both hinders the intestines from getting into the passage, and also the course of the fluids from being stopped in the vessels, which is secured in us by the cellular fulness and tense peritoneum: And it may be worth while to observe, that this process remains almost unaltered, even after the animal has been almost exhausted of fat.

There is next a passage quite down into the cavity where the testicles lie. Had the same structure obtained in man, by the constant drilling down of the liquor which is secreted for the lubricating of the guts, we should always have laboured under an hydrocele; but their posture secures them from any hazard of this kind: indeed your very fat lap-dogs, who consequently have an overgrown omentum, are sometimes troubled with an epiplocele.

The scrotum is shorter and not so pendulous as the Scrota human in all the dog kind that want the vesicula seminales, that the seed at each copulation might the sooner be brought from the testes, thus in some measure supplying the place of the vesiculae seminales; for the The vessels of the seed through the vasa deferentia is thus culea femi-shortened, by placing the secreting vessels nearer the nates, how excretory organs. Perhaps its passage is likewise quickened by the muscular power of the vasa deferentia, which is stronger in this creature than in man. The want of vesiculae seminales at the same time explains the reason why this creature is so tedious in copulation. But why these bodies are absent in the dog kind more than in other animals, is a circumstance we know nothing of.

The structure of the testicles is much the same with the human; as are likewise the corpus pyramidale, varicoform, or pampiniforme, and the epididymis or excretory vessel of the testicle. The vasa deferentia enter the the abdomen where the blood-vessels come out; and, passing along the upper part of the bladder, are inserted a little below the bulbous part of the urethra.

The preputium has two muscles fixed to it: one that arises from the sphincter ani, and is inserted all along the penis; and this is called retractor preputii. But the other, whose office is directly contrary to this, is cutaneous; and seems to take its origin from the muscles of the abdomen, or rather to be a production of their tunica carnoa. The corpora cavernosa rise much in the same way as the human; but these soon terminate; and the rest is supplied by a triangular bone, in the inferior part of which there is a groove excavated for lodging the urethra. There are upon the penis two protuberant bulbous fleshy substances, resembling the glans penis in man, at the back of which are two veins, which by the erectores penis and other parts are comprimed in the time of coition; and the circulation being stopped, the blood diffuses the large cavernous bodies. After the penis is thus swelled, the vagina by its contraction and swelling of its corpus cavernosum, which is considerably greater than in other animals, gripes it closely; and so the male is kept in action some time contrary to his will, till time be given for bringing a quantity of seed sufficient to impregnate the female; and thus, by that organmus veneris of the female organs, the want of the vesicula seminalis are in some measure supplied. But as it would be a very uneasy posture for the dog to support himself solely upon his hinder feet, and for the bitch to support the weight of the dog for so long a time; therefore, as soon as the bulbous bodies are sufficiently filled, he gets off and turns averse to her. Had, then, the penis been pliable as in other animals, the urethra must of necessity have been comprimed by this twisting, and consequently the course of the seed intercepted; but this is wisely provided against by the urethra's being formed in the hollow of the bone. After the emission of the seed, the parts turn flaccid, the circulation is restored, and the bulbous parts can be easily extracted.

The proflata seems here divided into two, which are proportionably larger than the human, and afford a greater quantity of that liquid.

The uterus of multiparous animals is little else but a continuation of their vagina, only separated from it by a small ring or valve. From the uterus two long canals mount upon the loins, in which the foetus are lodged: these are divided into different faces, which are strongly constricted betwixt each foetus; yet these constrictions give way in the time of birth. From these go out the tube Fallopianae, so that the ovaria come to lodge pretty near the kidneys.

We ought next to examine the structure of the thorax and its contents. But first it may not be amiss to remark of the diaphragm in its natural situation, that it is in general more loose and free than the human; which is owing to its connection with the neighbouring parts in a different manner from ours. The human diaphragm is connected to the pericardium; which again, by the intervention of the mediastinum, is tied to the sternum, spine, &c. but here there is some distance between the diaphragm and pericardium. We observe further, that its middle part is much more moveable, and the tendinous parts not so large. And indeed it was necessary their diaphragm should be somewhat loose, they making more use of it in difficult respiration than man. This we may observe by the strong heaving of the flanks of an horse or dog when out of breath; which corresponds to the rising of the ribs in us.

The disposition and situation of the mammae vary as they bear one or more young. Those of the uniparous kind have them placed between the posterior extremities, which in them is the highest part of their bodies, whereby their young get at them without the inconvenience of kneeling: Nevertheless, when the creatures are of no great size, and their breast large, as in sheep, the young ones are obliged to take this posture. In multiparous animals, they must have a great number of nipples, that their several young ones may have room at the same time, and these disposed over both thorax and abdomen; and the creatures generally lie down when the young are to be suckled, that they may give them the most favourable situation. From this it does not appear to be from any particular fitness of the vessels at certain places for giving a proper nourishment to the child, that the breasts are so placed in women as we find them, but really from that situation being the most convenient both for mother and infant.

The sternum is very narrow, and consists of a great number of small bones, moveable every way; which always happens in creatures that have a great mobility in their spine. The ribs are straighter, and by no means to convex as the human; whereby in respiration the motion forward will very little enlarge their thorax, which is compensated by the greater mobility of their diaphragm; so our thorax is principally enlarged according to its breadth and depth, and theirs according to its length. The want of clavicles, and the consequent falling in of the anterior extremities upon the chest, may contribute somewhat to the straightness of the ribs.

The mediastinum in this creature is pretty broad. The pericardium is not here contiguous to the diaphragm, but there is an inch of distance betwixt them, in which place the small lobe of the lungs lodges; and by this means the liver, &c. of this animal, though continually pressing upon the diaphragm, yet cannot disturb the heart's motion.

The heart is situated with its point almost directly downwards, according to the creature's posture, and is but very little inclined to the left side. Its point is much sharper, and its shape more conoidal, than the human. Here the names of right and left ventricles are proper enough, though not so in the human; which ought rather to be called anterior and posterior, or superior and inferior. The animal has the vena cava of a considerable length within the thorax, having near the whole length of the heart to run over ere it gets at the sinus Louvierianus dexter. In men, as soon as it pierces the diaphragm, so soon it enters the pericardium, which is firmly attached to it, and immediately gets into the sinus Louvierianus; which sinus, in the human subject, by the oblique situation of the heart is almost contiguous to the diaphragm: and by this we discover, that several authors have taken their delineations of the human heart from brutes; which is easily detected by the shape and situation of the heart, and long vena cava, within the thorax. This was one of the faults of the curious wax-work that were shown at London and Paris, which were plainly taken from a cow. This situation of the heart of the creature agrees best with the shape of its thorax, which is lower than the abdomen.

The cegrets of the large blood-vessels from the heart is somewhat different from the human: For here the right subclavian comes off first; and as a large trunk runs some way upwards before it gives off the left carotid, and splits into the carotid and subclavian of the right side, then the left subclavian is sent off. So that neither here, properly speaking, is there an aorta ascendens, more than in the human; but this name has probably been imposed upon it from observing this in a cow, where indeed there is an ascending and descending aorta.

From this specialty of the distribution of the vessels of the right side, which happens, though not in so great a degree, in the human subject, we may perhaps in some measure account for the general greater strength, readiness, or facility of motion, which is observable in the right arm. Upon measuring the sides of the vessels, the surface of the united trunk of the right subclavian and carotid is less than that of the left subclavian and carotid, as they are separated. If so, the resistance to the blood must be less in that common trunk than in the left subclavian and carotid: But if the resistance be smaller, the absolute force with which the blood is sent from the heart being equal, there must necessarily be a greater quantity of blood sent through them in a given time; and as the strength of the muscles is, ceteris paribus, as the quantity of blood sent into them in a given time, those of the right arm will be stronger than those of the left. Now children, being conscious of this superior strength, use the right upon all occasions; and thus from use comes that great difference which is so observable. That this is a sufficient cause, seems evident from fact; for what a difference is there betwixt the right and the left arm of one who has played much at tennis? View but the arms of a blacksmith and legs of a footman, and you will soon be convinced of this effect arising from using them. But if by any accident the right arm is kept from action for some time, the other from being used gets the better; and those people are left-handed: For it is not to be imagined, that the small odds in the original formation of the vessels should be sufficient to resist the effect of use and habit (instances of the contrary occur every day); it is enough for our present argument, that where no means are used to oppose it, the odds are sufficient to determine the choice in favour of the right. Now because it is natural to begin with the leg corresponding to the hand we have most power of, this is this what gives also a superiority to the right leg.

This difference is not peculiar to man, but is still more observable in those creatures in whom the same mechanism does obtain in a greater degree. Do but observe a dog at a trot, how he bears forward with his right side; or look at him when a-scraping up anything, and you will presently see that he uses his right much oftener than he does his left foot. Something analogous to this may be observed in horses. It has been the opinion of some anatomists, that left-handed people, as well as those distinguished by the name of ambidexter (who use both hands alike), have the two carotid and subclavian arteries coming off in four distinct trunks from the arch of the aorta: but no appearance of this kind has ever been observed in such bodies as have been examined for this purpose; though indeed these have been but few, and more experience might throw greater light on the subject.

The thymus of this creature is proportionally much larger than ours: whereas the glandula thyroidea is much less, and is divided into two distinct parts, or thyroids, there are two separate glands; which is not the case in man. The reason of this difference is unknown, as is likewise the use of the gland itself. It is generally remarked, that these two glands do thus always supply the place of each other; that is, in such animals as have a large thymus, the glandula thyroidea is smaller, and vice versa. Hence we are naturally led to ascribe the same use to both, viz., the separation of a thin lymph for diluting the chyle in the thoracic duct before it be poured into the blood; then if we consider the different formation of the thorax in both, we shall readily account for the variety in the bulk of these two glands. Respiration being chiefly performed in man by the widening of the chest, the lungs at every inspiration must press upon the thymus, and consequently diminish it; but the diaphragm yielding more in the dog's inspiration, this gland is not so much pressed by the lungs, and so will be larger; and hence the glandula thyroidea will be proportionally less. Again, from the posture of this creature, we shall see that it was much more convenient for a dog to have the most part of the diluting lymph supplied by the thymus, since the neck being frequently in a descending posture, the lymph of the thyroid gland would have a very disadvantageous course to get to the thoracic duct; whereas in the human body, the thymus is really below the lacteal canal, where it makes its curvature before it opens into the subclavian; and consequently there is a necessity of a considerable share of the diluting liquor being furnished by the thyroid gland, which is situated much higher; so that its lymph has the advantage of a perpendicular descent.

We may here observe, that the thoracic duct in a dog has no curvature before it enters the subclavian vein, thoracicus, the horizontal position of this animal allowing a favourable enough course to the chyle, so as not to need that turn to force its passage into the blood. It may likewise be observed, that such animals as walk horizontally have the valves of the thoracic duct fewer in number than others. The horse has only a single pair; while, on the contrary, the ape resembles man in having several valves. Thus the lymph is not only forwarded in its passage, but the weight of the column is diminished. The lungs of this creature are divided into more numerous lobes, and deeper, than they are in man, for the same reason as the liver. The left side of the thorax in this animal bears a greater proportion to the right than in man; the one being nearly as three to two, the other as four to three. In quadrupeds, as well as in man, the lungs are closely applied to the containing parts; although this has been denied by some.

We look on it as a general rule, that all quadrupeds, as having occasion to gather their food from the ground, are provided with longer necks than man: but as a long neck not only gives the advantage of too long a lever to the weight of the head, but also, when the animal is gathering his food, makes the brain in danger Of Quadra- of being oppressed with too great a quantity of blood, by the liquor in these arteries having the advantage of a descent, while that in the veins must remount a considerable way contrary to its own gravity; it was therefore necessary that a part of the length of the neck should be supplied by the length of the jaws. Thus we see horses, cows, &c., who have no occasion for opening their mouths very wide, yet have long jaws. Bulldogs, indeed, and such animals as have occasion for very strong jaws, must of necessity have them short; because the longer they are, the facility to be overcome acts with a longer lever. Another exception to this general rule, is such animals as are furnished with something analogous to hands to convey their food to their mouths, as cats, apes, &c. The teeth of this creature plainly show it to be of the carnivorous kind; for there are none of them made for grinding its food, but only for tearing and dividing it. It has six remarkable sharp teeth before, and two very long tusks behind; both of which the ruminating animals want. These are evidently calculated for laying very firm hold of substances, and tearing them to pieces; and the vast strength of the muscles inserted into the lower jaw, assists greatly in this action; while the molars have sharp cutting edges, calculated for cutting flesh, and breaking the hardest bones. Even its posterior teeth are not formed with rough broad surfaces as ours are; but are made considerably sharper, and press over one another when the mouth is shut, that so they may take the firmer hold of whatever comes betwixt them.

The tongue, in consequence of the length of the jaws, is much longer than ours; and as this creature feeds with his head in a depending posture, the bolus would always be in danger of falling out of the mouth, were it not for several prominences or papillae placed mostly at the root of the tongue, and crooked backwards in such a manner as to allow anything to pass easily down to the jaws, but to hinder its return. By the papillae also the surface of the tongue is increased, and a stronger impression is made on the sensation of taste. In some animals who feed on living creatures, these tentoon-hooks are still more conspicuous; as in several large fishes, where they are almost as large as their teeth in the forepart of their mouth, and near as firm and strong.

When we open the mouth, we see the amygdala very prominent in the posterior part of it; so that it would appear at first view, that these were inconveniently placed, as being continually exposed to injuries from the hard substances this creature swallows; but upon a more narrow scrutiny, we find this provided for by two membranous capsules, into which the amygdala, when pressed, can escape, and remove themselves from such injuries.

The valum pendulum palati is in this creature considerably longer than in man, to prevent the food from getting into his nose; which would happen more frequently in this animal than in man, because of its situation while feeding.

In this subject, as well as in other quadrupeds, there is no uvula; but then the epiglottis, when pressed down, covers the whole rima entirely, and naturally continues so; there is therefore a ligament, or rather muscle, that comes from the os hyoideum and root of the tongue, that is inserted into that part of the epiglottis where it is articulated with the cricoid cartilage, which serves to raise it from the rima, though not so strongly but that it may with a small force be clapped down again.

It may be asked, however, Why the uvula is wanting here, and not in man? This seems to be, that the quadrupeds, who swallow their food in an horizontal situation, have no occasion for an uvula, though it is necessary in man on account of his erect situation.

In the upper part of the pharynx, behind the cricoid cartilage, there is a pretty large gland to be found, which serves not only for the separation of a mucous liquor to lubricate the bolus as it passes this way, but also supplies the place of a valve, to hinder the food from regurgitating into the mouth, which it would be apt to do by reason of the descending situation of the creature's head. In man, the muscle of the epiglottis is wanting, its place being supplied by the elasticity of the cartilage.

The oesophagus is formed pretty much in the same way as the human. Authors indeed generally allege, that quadrupeds have their gullet composed of a double row of spiral fibres decussating one another; but this is peculiar to ruminating animals, who have occasion for such a decussation of fibres. The action of these you may easily observe in a cow chewing her cud.

The nose is generally longer than in man, and its external passage much narrower. The internal structure is also better adapted for an acute smelling, having a larger convoluted surface on which the membrana scharaderiana is spread; and this is to be observed in most quadrupeds, who have the os spongiosum commonly large, and these too divided into a great number of excessively fine thin lamellae. The sensibility seems to be increased in proportion to the surface; and this will also be found to take place in all the other senses. The elephant, which has a head pretty large in proportion to its body, has the greatest part of it taken up with the cavity of the nose and frontal sinuses; which last extend almost over their whole head, and leave but a small cavity for their brains. A very nice sense of smelling was not absolutely necessary for man, who has judgment and experience to direct him in the choice of his food; whereas brutes, who have only their senses, must of necessity have these acute, some having one sense in greater perfection than others, according to their different way of life. We not only conclude a priori from the large expanded membrana scharaderiana, that their sense of smelling is very acute, but we find it so by cows and horses distinguishing so readily between noxious and wholesome herbs, which they do principally by this sense.

The external ear in different quadrupeds is differently framed, but always calculated to the creature's manner of life. In shape it commonly resembles the oblique section of a cone from near the apex to the basis. Hares, and such other animals as are daily exposed to insults from beasts of prey, have large ears directed backwards, their eyes warning them of any danger before; rapacious animals, on the other hand, have their ears placed directly forwards, as we see in the lion, cat, &c. The slow hounds, and other animals that are designed to hear most distinctly the sounds coming from below, have their ears hanging downwards; or their ears are flexible, because they move... Of Quadrupeds their head for the most part with greater difficulty than man. Man, again, who must equally hear sounds coming from all quarters, but especially such as are sent from about his own height, has his external ear placed in a vertical manner, somewhat turned forward. In short, wherever we see a specialty in the make of this organ in any creature, we shall, with very little reflection, discover this form to be more convenient for that creature than another. The animal also has the power of directing the cone of the ear to the fororous body without moving the head. There are some differences to be observed in the structure of the internal ear in different animals; but we know so very little of the use of the particular parts of that organ in the human subject, that it is altogether impossible to assign reasons for these variations in other creatures.

All quadrupeds have at the internal canthus of the eye a strong firm membrane with a cartilaginous edge, which may be made to cover some part of their eye; and this is greater or less in different animals as their eyes are more or less exposed to dangers in searching after their food. This membrana nictitans, as it is called, is not very large in this animal. Cows and horses have it so large as to cover one half of the eye like a curtain, and at the same time is transparent enough to allow abundance of the rays of light to pass through it. Fishes have a cuticle always over their eyes, as they are ever in danger in that inconstant element. In this then we may also observe a sort of gradation.

All quadrupeds have a seventh muscle belonging to the eye, called jupenforius. It surrounds almost the whole optic nerve, and is fixed into the sclerotic coat as the others are. Its use is to sustain the weight of the globe of the eye, and prevent the optic nerve from being too much stretched, without obliging the four straight muscles to be in a continual contraction, which would be inconvenient; at the same time this muscle may be brought to assist any of the other four, by causing one particular portion of it to act at a time.

The next thing to be remarked is the figure of the pupil, which is different in different animals, but always exactly accommodated to the creature's way of life, as well as to the different species of objects that are viewed. Man has it circular, for obvious reasons: an ox has it oval, with the longest diameter placed transversely, to take in a larger view of his food; cats, again, have theirs likewise oval, but the longest diameter placed perpendicularly; they can either exclude a bright light altogether, or admit only as much as is necessary. The pupil of different animals varies in wideness, according as the internal organs of vision are more or less acute: Thus cats and owls, who seek their prey in the night, or in dark places (and consequently must have their eyes so formed as that a few rays of light may make a lively impression on the retina), have their pupils in the day-time contracted into a very narrow space, as a great number of rays would oppress their nice organs; while in the night, or where the light is faint, they open the pupil, and very fully admit the rays. In the same way, when the retina is inflamed, a great number of rays of light would occasion a painful sensation; therefore the pupil is contracted: on the contrary, in dying people, or in a beginning amaurosis, it is generally dilated, as the eyes on such occasions are very difficultly affected, and as it were insensible.

The posterior part of the choroid coat, which is called tapetum, is of different colours in different creatures. For oxen, feeding mostly on grass, have this membrane of a green colour, that it may reflect upon the retina all the rays of light which come from objects of that colour, while other rays are absorbed: Thus the animal sees its food better than it does other objects. Cats and owls have their tapetum of a whitish colour; and for the same reasons have the pupil very dilatable, and their organs of vision acute: And we shall find, that all animals see more or less distinctly in the dark, according as their tapetum approaches nearer to a white or black colour. Thus dogs, who have it of a greyish colour, distinguish objects better in the night than man, whose tapetum is dark brown; and who, it is believed, sees worst in the dark of any creature: it being originally designed that he should rest from all kinds of employment in the night-time. The difference then of the colour of the tapetum, as indeed the fabric of any other part in different creatures, always depends on some particular advantage accruing to the animal in its peculiar manner of life from this singularity.

We shall now proceed to the brain, which we remark in the first place is proportionally much smaller in all quadrupeds than the human; but, as in man, it is divided into cerebrum and cerebellum, and these two parts bear nearly the same proportion to one another as in us. There was no such occasion for so great a quantity of brain in those animals as in man; seeing in them all its energy is employed in their progression, while man has a great waste of spirits in the exercise of his reason and intellectual faculties. And besides all this, a great bulky brain would be inconvenient to these creatures, in so far as it would add considerably to the weight of the head; which having the advantage of a long lever to act with, would require a much greater force to support it than now it does; for the heads of the greatest part of quadrupeds are not near so heavy as they would at first seem to be, from the sinus frontales being produced a great way upwards to enlarge the organs of smelling.

The pits in the anterior part of their skulls are much more conspicuous than in the human cranium; which may be occasioned by the depending posture of these creatures' heads while they gather their food: the brain at this time gravitating much on the bones while they are as yet soft, will gradually make impressions upon them at these places where it rises into eminences. This is prevented in man mostly by his erect posture.

The falk is not near so large in quadrupeds as in man, as they have little occasion to lie on either side, and the two hemispheres of the brain are in a great measure hindered from jutting against one another in violent motions, by the brain's infusing itself into the above mentioned pits.

The second process of the dura mater, or tentorium cerebello super-expansum, is considerably thicker and stronger in most quadrupeds than in man; especially in such of them as are very swift of foot, as hares and rabbits, and that most when they are old. This mem- Of Quadru-brane is generally ossified, or we find the place of it supplied by a bone, that it may the more effectually keep off the superincumbent brain from the cerebrum in their rapid motions, which otherwise would be of bad consequence.

The olfactory nerves are very large, and justly deserve the name of processus manillares. They are hollow, and consist of a medullary and cineritious substance, and at first sight appear to be the anterior ventricles of the brain produced; but in man they are small, and without any discernible cavity. The reason of this is pretty evident, if we consider how this animal's head is situated; for the lymph continually gravitating upon the inferior part of the ventricles, may thus elongate and produce them; but from this very inferior part the olfactory nerves rise, and are sent immediately through the os ethmoides into the nose. Hence the ancients, thinking they were continued hollow into the nose, believed they were the emunctories of the brain; in the brain of sheep, which by its firm texture is the best subject of any for searching into the structure of this part, we evidently see, that the name of the sigmoid cavity was very properly applied by the ancients to the lateral ventricles of the brain; which are really of a greater extent than they are ordinarily painted by the anatomists, reaching farther backwards, and forwards again under the substance of the brain. The cortical and medullary parts, as well as the corpus callosum, are similar to those parts in man.

The noses and testes deserve this name much better here than in the human body, with respect to each other. They are larger in the quadruped; and hence we perceive that there is no great reason for attributing the different operations to any particular size or shape of these parts. They are here also of different colours; the noses being of the colour of the cortical, and the testes of the medullary substance of the brain; whereas in man they are both of one colour. The reason of these differences, and others of the like nature to be met with, we shall not pretend to determine; for we have hitherto such an imperfect knowledge of the brain itself, that we are entirely ignorant of the various uses of its different parts. We may in general conclude, that the varying in one animal from what it is in another, is fitted to the creature's particular way of living.

The rete mirabile Galeni, situated on each side of the fella turcica, about which there has been so much dispute, is very remarkable in most quadrupeds. This plexus of vessels is nothing else than a continuation of the internal carotid arteries, which, entering the skull, divide into a vast number of minute branches running along the side of the fella turcica; and, uniting afterwards, are spent on the brain in the common way. Galen seems with justice to suppose, that this plexus of vessels serves for checking the impetuosity of the blood destined for the brain.

The structure of the brain differing but very little in all quadrupeds, it will be needless to examine it in any other.

Sect. IV. The Anatomy of a Cow.

The next species of quadrupeds we propose to consider was the ruminant kind, of which we have an example in a cow; and accordingly shall take the fetus of Quadrupeds.

Of course, the uterus differs from the human, in having two pretty large cornua. This is common to it with other brutes; for a bitch has two long cornua uteri. But these again differ (as being multiparous teri. and uniparous) in this, that in the bitches cornua the fetus are contained; whereas here there is only part of the fecundities, being mostly the allantois with the included liquor. The muscular fibres of the uterus are more easily discovered; its internal surface has a great number of spongy, oblong, protuberant, glandular bodies fixed to it. These are composed of vessels of the uterus terminating here. In an impregnated uterus, we can easily press out of them a chylous mucilaginous liquor; they are composed of a great many processes or digituli, and deep caverns, answering to as many caverns and processes of the placenta. Their resemblance has occasioned the name of papilla to be given them; and hence it was that Hippocrates was induced to believe that the fetus sucked in utero. The papillae are found in all the different stages of life, in the various stages of pregnancy, and likewise in the unimpregnated state. It is not easy to determine whether the uterus grows thicker or thinner in the time of gestation. The membranes, it is plain (by the stretching of the parts), must be made thinner; but then it is as evident, that the vessels are at that time enlarged, upon which principally the thickness of any part depends; so there seems to be as much gained the one way as lost the other.

The os uteri is entirely shut up by a glutinous mucilaginous substance, that is common to the females of all creatures when with young: by this the external air is excluded, which would soon make the liquors corrupt; it also prevents the inflammation of the membranes, and the hazard of abortion. By this means also the lips of the womb are kept from growing together, which otherwise they would certainly at this time do. There are mucous glands placed here to secrete this glutin, which on the breaking of the membranes with the contained waters make a sapo that lubricates and waxes the parts, and makes them easily yield. The first of the proper involucra of the fetus is the chorion.

The chorion is a pretty strong firm membrane, on whose external surface are dispersed a great many red fleety bodies of the same number, size, and structure, with the papillae, with which they are mutually indented. They have been called cotyledones, from Kothos, Cotyledon, "cavity." This is greatly disputed by some as a name very improper; but we think without reason, since the surface that is connected to the papillae is concave, though when separated it appears rather convex. To thus all dispute, they may be called properly enough placentulae, since they serve the same use as the placenta in women. The separation of these from the papillae without any laceration, and our not being able Of Quadru- to inject coloured liquors from the vessels of the glands of the uterus into the placenta, seem to prove beyond a reply, that there can be here no anastomoses between the vessels; on their coats run a great number of vessels that are sent to the several placentae, on the external side next to the uterus; whereas in creatures that have but one placenta, as in the human subject, cats, dogs, &c., the adhesion is somewhat firmer: The placentae are likewise joined to the papillae in the cornua uteri. We shall next give the history of the allantois.

This is a fine transparent membrane contiguous to the former. It is not a general involucrum of the fetus in the mother, for it covers only a small part of the amnios. It is mostly lodged in the cornua uteri. In mares, bitches, and cats, it surrounds the amnios, being everywhere interposed between it and the chorion. In sheep and goats it is the same as in this animal; and in swine and rabbits it covers still less of the amnios. This sac is probably formed by the dilatation of the urachus, which is connected at its other end to the fundus of the bladder, through which it receives its contents; and a great quantity of urine is commonly found in it. The membrane is doubled at the extremity of the canal, to hinder the return of the urine back into the bladder. Its vessels are so excessively fine and few, that we cannot force an injected liquor farther than the beginning of this coat. This membrane is so far analogous to the cuticle, as not to be liable to corruption, or easily irritated by acrid liquors.

The existence of this membrane in women has been very warmly disputed on both sides. Those who are against its existence deny they could ever find it; and allowing it were so, allege, that since the urachus is impervious, as appears by our not being able to throw liquors from the bladder into it, or vice versa, it cannot serve the use that is agreed by all it does serve in beasts; and therefore in the human body there is no such thing. But if we consider, on the other hand, first, that there seems to be the same necessity for such a reservoir in man as in other animals; secondly, that we actually find urine contained in the bladder of the human fetus; thirdly, that urine has been evacuated at the navel when the urethra was stopped, which urine without this conduit would have fallen into the cavity of the abdomen; fourthly, that midwives have pretended to remark two different sorts of waters come away at the time of birth; and, lastly, that Dr Littre and Dr Hale have given in this membrane of an human subject, with all the other secundines curiously prepared, the one to the royal academy at Paris, the other to the royal society at London; by which societies their respective accounts are attested; not to mention Verheyen, Heister, Keill, &c., who affirm their having seen it; and Mr Albinus, that famous anatomist, professor at Leyden, is said to have shown to his college every year a preparation of it: On all these accounts it seems most probable, that there is such a membrane in the human body.

The third proper integument of the fetus is the amnios. It is thinner and firmer than the chorion; it has numerous ramifications of the umbilical vessels spread upon it, the lateral branches of which separate a liquor into its cavity. This is the proper liquor of the amnios: which at first is in a small quantity, afterwards increases for some months, then again decreases; and in a cow near her time, the quantity of this liquor is not above a pound. This membrane does not enter the cornua uteri in this creature, being confined to the body of the uterus; whereas the allantois occupies chiefly its cornua. But for what further relates to the structure of the involucra, with the nature of the liquors contained in them, we must refer to the second volume of Medical Essays, from page 121, where you have the sum of all we know of this matter.

There are here two vena umbilicales, and but one in the human subject; because the extreme branches coming from the several placentae could not unite so soon as they would have done had they come all from one case as in the human.

There is a small round fleshy body that swims in the urine of this creature, mares, &c., which is the hippomanes of the ancients. Several idle opinions and whims have been entertained as to its use; but that seems to be still unknown, or how it is generated or nourished, for it has no connection with the fetus or placentae.

Having thus considered the several involucra of this animal in a fetus state, let us next observe the peculiarities in its internal structure peculiar to a fetus.

The umbilical vein joins the vena portarum in the venacapsula Glissoniana, without sending off any branches, as it does in the human subject. This vein soon after birth turns to a ligament; yet there are some instances where it has remained pervious for several years after birth, and occasioned a hemorrhage. We may next observe the duct called canalis venosus, going straight from the capsula Glissoniana to the vena cava inferior; this turns also afterwards to a ligament. The umbilical arteries rise at acute angles from the internal iliacs, whatever form may lay to the contrary; these also become impervious.

The pulmonary artery coming from the right ventricle of the heart divides into two; the larger, called canalis arteriosus, opens into the descending aorta; the other divides into two, to serve the lungs on each side.

The foramen ovale is placed in the partition between the right and left auricles. At the edge of the hole oval, is fixed a membrane, which when much stretched will cover it all over; but more easily yields to a force that acts from the right auricle to the left, than from the left to the right. After what has been said, we may easily understand how the circulation is performed in a fetus. The blood, being brought from the placenta of the mother, is thrown into the capsula Glissoniana, where it is intimately blended with the blood in the performed vena portarum; then part of this blood goes directly into the vena cava by the ductus venosus; the rest passes through the liver. First, then, the whole is sent from the vena cava into the right auricle, from whence part of it is sent by the foramen ovale into the left auricle; the rest passes into the right ventricle, then into the pulmonary artery; then the greatest share it receives is sent immediately into the descending aorta by the canalis arteriosus, and the remainder circulates through the lungs, and is sent back by the pulmonary veins into the left auricle; which, with the blood brought there by the foramen ovale, is sent into the left ventricle, from whence it is driven by the aorta through the Chap. I.

Of Quadrupeds.

The great design of this mechanism is, that the whole mass of blood might not pass through the collapsed lungs of the fetus; but that part of it might pass through the foramen ovale and canalis arteriosus without circulating at all through the lungs.

This was the opinion that universally prevailed till the end of the last century, when it was violently opposed by Monsieur Mery, who is veryingular in several of his opinions. He will not allow that the foramen ovale transmits blood from the right to the left auricle, but on the contrary from the left to the right; and that for no other reason but because he observed the pulmonary artery in a fetus larger than the aorta.

Mr Winiford endeavours to reconcile these two opinions, by saying the blood may pass either way, and that it is here as it were blended; his reason is, that on putting the heart in water, the foramen ovale transmits it any way. Mr Rohault, professor of anatomy at Turin, and formerly one of Mery's scholars, strongly defends his matter, and criticizes Mr Winiford. What he principally builds on, is the appearance this foramen has in some dried preparations: This Mr Winiford will not allow as a proof. After all, the common opinion seems most probable; and that for the following reasons: First, the pulmonary artery being larger signifies nothing, since its coats are not only thinner and will be more easily defended, but also the resistance to the blood in the pulmonary artery from the collapsed lungs is greater than the resistance to the blood in the aorta. Secondly, if we should allow any of these two uncommon opinions, we should have the right ventricle vastly more capacious than the left: For if we suppose the foramen ovale to be capable of transmitting one-third of the whole mass of blood in any given time, and the canalis arteriosus as much in the same time, then you will find, that, according to Mr Mery's opinion, the whole mass of blood being driven from the right ventricle into the pulmonary artery, one-third passes by the canalis arteriosus into the descending aorta, two-thirds passing through the lungs and returning into the left auricle; one-half of which portion, or one-third of the whole mass, passes by the foramen ovale into the right auricle; and the other, or the last third, will be sent into the left ventricle, and thence expelled into the aorta; which third, with that from the pulmonary artery by the canalis arteriosus, circulating through the body, are returned into the right auricle, where meeting with the other third from the foramen ovale, with it they are sent into the right ventricle to undergo the same course. Thus the whole mass is expelled by the right ventricle, and only one-third by the left. If this was the case, why is not the right ventricle three times as large and strong as the left?

Then if, according to Mr Winiford's system, the foramen ovale transmits equal quantities from both auricles, this comes to the same as if there was no foramen ovale at all: that is to say, the whole mass going from the right auricle into the right ventricle and pulmonary artery, one-third of the whole mass passes into the aorta through the canalis arteriosus; the other two-thirds, passing through the lungs, return to the left auricle and ventricle. Thus the right ventricle expels the whole mass; the left, only two-thirds.

But if, according to the common opinion, we suppose the foramen ovale to convey the blood from the right to the left auricle, then one-third passes this way into the left ventricle; the other two-thirds are sent by the right ventricle into the pulmonary artery: from whence one-third passes by the canalis arteriosus into the aorta descendens; the other third circulates through the lungs, and is returned into the left ventricle; where meeting with that from the foramen ovale, it is therewith expelled into the aorta, and with the one-third transmitted by the canalis arteriosus returns into the right auricle to run the same race as before. Thus we conclude, that two-thirds are expelled by each ventricle, and the whole circulates through the body; and hence they come to be of pretty equal dimensions. In all this calculation no regard has been had to the blood discharged from the umbilical vessels; but the greater quantity returned by the veins, than sent out by the arteries, still argues for the common opinion.

The kidneys in the fetus are composed of different lobes, which serve to give us an idea of the kidneyneys, being a congeries of different glands; these lobes being kept contiguous by the external membrane, are pressed by the other viscera, till at length they unite.

We now come to consider the creature as a ruminant animal. There are no dentes incisores in the upper jaw; but the gums are pretty hard, and the tongue rough. This roughness is occasioned by long sharp pointed papillae, with which the whole substance of it is covered. These papillae are turned towards the throat; so that by their means the food, having once got into the mouth, is not easily pulled back. The animals therefore supply the defect of teeth by wrapping their tongue round a tuft of grass; and so, pressing it against the upper jaw, keep it stretched, and cut it with the teeth of the under jaw; then, without chewing, throw it down into the oesophagus, which in these creatures consists of a double row of spiral fibres decalcifying one another. All animals which ruminate must have more ventricles than one; some have two, some three; our present subject has no less than four. It has four stomachs. The food is carried directly down into the first, which lies upon the left side, and is the largest of all; it is called ventriculus, and xystus, by way of eminence. Their names and description.

It is what is called by the general name of paunch by names and the vulgar. There are no rugae upon its internal surface; but instead of these there are a vast number of small blunt-pointed processes, by which the whole has a general roughness, and the surface is extended to several times the size of the paunch itself. The food, by the force of its muscular coat, and the liquors poured in here, is sufficiently macerated; after which it is forced up hence by the oesophagus into the mouth, and there it is made very small by mastication; this is what is properly called chewing the cud, or rumination; for which purpose the dentes molares are exceedingly well fitted: for instead of being covered with a thin crust, the enamel on them consists of perpendicular plates, between which the bone is bare, and constantly wearing faster than the enamel, so that the tooth remains good to extreme old age; and by means of these teeth the rumination is carried on for a long time without any danger of spoiling them. After rumination, the food is sent down by the gullet into the second stomach; for the oesophagus opens indifferently into both. It ends exactly where the two stomachs meet; and there is a smooth gutter with ring. Of Quadrupeds which leads into the second stomach, from thence to the third, and also to the fourth; however, the creature has a power to direct it into which it will. Some tell us, that the drink goes into the second; but that might be easily determined by making them drink before slaughter. The second stomach, which is the anterior and smaller, is called *reticulum*, *honeycomb*, or *king's hood*. It consists of a great number of cells on its internal surface, of a regular pentagonal figure, like to a honeycomb. Here the food is farther macerated; from which it is protruded into the third, called *vesica* or *omacum*, vulgarly the *manyplies*, because the internal surface rises up into a great many plicae or folds, and *fratum super fratum*, according to the length of this stomach. Some of these plicae are farther produced into the stomach than others; i.e., first two longer ones on each side, and within these two shorter in the middle, &c. There are numberless glandular grains like millet-seeds dispersed on its plicae, from which some authors call this stomach the *millet*. From this it passes into the fourth, whose names are *vesiga*, *abomasum*, *caillie*, or the red, which is the name it commonly has because of its colour. This much resembles the human stomach, or that of a dog; only the inner folds or plicae are longer and looser; and it may also be observed, that in all animals there is only one digestive stomach, and that has the same coagulating power in the fetus as the fourth stomach in this animal; whence this might not improperly be called the only true stomach. *Caillie* signifies curdled; and hence the French have given that as a name to this fourth stomach, because any milk that is taken down by young calves is there curdled. It is this fourth stomach, with the milk curdled in it, that is commonly taken for making rennet; but after the bile and pancreatic juice enter, this coagulation is not to be found, which shows the use of these liquors. There are other creatures which use the same food, that have not such a mechanism in their digestive organs. Horses, asses, &c. have but one stomach, where grass is macerated, and a liquor for their nourishment extracted, and the remainder sent out by the anus very little altered. From this different structure of the stomach in these creatures, a ruminant animal will be served with one-third less food than another of equal bulk: graziers are sufficiently acquainted with this. The reason is, that ruminating animals have many and strong digestive organs; all their food is fully prepared, and almost wholly converted into chyle: But a horse's stomach is not fitted for this; so that he requires a much greater quantity of food to extract the same nourishment.

The guts of these creatures are of a considerable length in proportion to the bulk of the body; and this confirms what we said formerly on the subject of the intestines of a dog, viz. that the length and capacity of the guts were different in different animals, according to the nature of their food.

The *duodenum* is formed here much the same way as in a dog, and the general intention kept in view with regard to the mixture of the bile and pancreatic lymph. The great guts here hardly deserve that name, their diameter differing very little from that of the small ones; but to compensate this, they are much longer proportionally than a dog's are, being convoluted as the small guts are. The *caecum* is very large and long. The digestion of the cow, as well as of some other animals, is accompanied with a peculiar kind of action called *ruminantia*; the intention of which seems to be, that the food may be sufficiently comminuted, and thus more fully acted upon by the stomach: for it is not observed that a calf ruminates as long as it is fed only upon milk, though the action takes place as soon as it begins to eat solid food. But it is to be observed, that as long as a calf feeds only upon milk, the food descends immediately into the fourth stomach (which, as has been already mentioned, seems only capable of performing the operation of digestion) without stopping in any of the first three. The rumination does not take place till after the animal has eaten a pretty large quantity; after which she lies down, if she can do it conveniently, and begins to chew; though the operation will take place in a standing posture, if she cannot lie down. In this action a ball is observed to rise from the stomach with great velocity, almost as if shot from a musket. This ball the animal chews very accurately, and then swallows it again, and so on alternately, till all the food she has eaten has undergone this operation. This is easily explained from the structure of the oesophagus, which has one set of fibres calculated for bringing up the grats, and another for taking it down.

By means of rumination, the cow extracts a much larger proportion of nourishment from her food than those animals which do not ruminate; and hence she is contented with much worse fare, and smaller quantities of it, than a horse; hence also the dung of cows, being much more exhausted of its fine parts than horse-dung, proves much inferior to it as a manure.

The *spleen* differs not much either in figure or situation from that of a dog's; but it is a little more firmly fixed to the diaphragm, there not being here so much danger of this viscus's being hurt in the flexions of the spine.

The *liver* is not split into so many lobes in this creature as either in a man or dog; which depends on the small motion this creature enjoys in its spine, which made such a division needless. This also confirms what we formerly advanced on this head.

Their *vesica urinaria* is of a pyramidal shape. It is very large, and more membranaceous; for the urine of these creatures not being so acid as that of carnivorous animals, there was no such occasion for expelling it so soon.

The male is provided with a loose pendulous *scrotum*, scrofula, and consequently with *vesicula seminalis*. The female *vesiculae* organs differ from those of a bitch, mostly as to the form of the cornua uteri, which are here contorted in form of a snail. In this, and all uniparous animals, they contain only part of the secundines; but in bitches, and other multiparous animals, they run straight up in the abdomen, and contain the fetus themselves.

The situation of the heart is pretty much the same with that of a dog, only its point is rather sharper: In us, the heart beating continually against the ribs, and both ventricles going equally far down to the constitution Chap. II. COMPARATIVE ANATOMY.

Of Fowls. The situation of the apex, it is very obtuse; but here the apex is made up only of the left ventricle, so is more acute.

The aorta in this creature is justly divided into ascending and descending, though this division is ill-founded either in a dog or man; and it has certainly been from this subject that the older anatomists took their descriptions when they made this division; for here the aorta divides into two, the ascending and descending.

CHAP. II. Of Fowls.

The next class of animals we come to consider are of the feathered kind; which are divided into the granivorous and carnivorous. But before we go on to consider the specialties in the viscera of each kind, we must observe what both species agree in.

Sect. I. Of Fowls in general.

Fowls have a particular covering of feathers different from all other creatures, but exactly well suited to their manner of life: for it not only protects them from the injuries of the weather, but serves them in their progression through that thin aerial element they are for the most part employed in; and as some fowls live much in the water, their feathers being continually befouled with an oily liquor, keeps the water from foaming into their skins, and so prevents the bad effects which it would infallibly otherwise produce.

Fowls have the strongest muscles of their whole bodies, how they are inserted into their wings; whence by the way we may observe, that it is altogether impossible for man to buoy himself up into the air like birds, even though he had proper machines in place of wings, unless he were likewise provided with muscles strong enough for moving them, which he has not. In the next place, their wings are not placed in the middle of their bodies, but a good deal further forwards; whence it would at first view appear, that their heads would be erect, and their posterior parts most depending when raised in the air; but by stretching out their heads which act upon the lever of a long neck, they alter their centre of gravity pretty much; and also by filling the sacs or bladders in the inside of their abdomen with air, and expanding their tail, they come to make the posterior part of their bodies considerably higher; and thus they fly with their bodies nearly in an horizontal situation. Hence we find, that if their necks are kept from being stretched out, or if you cut away their tails, they become incapable of flying any considerable way.

The largeness of the wings in different fowls varies according to the occasions of the creature. Thus birds of prey, who must fly a considerable way to provide their food, have large strong wings; whereas domestic birds, who find their nourishment almost everywhere, have very short and but small wings. Their tail is of use in afflicting to raise them in the air; though the chief purpose of it is to serve as a rudder in guiding their flight, whilst they use their wings as we do oars in putting forward a boat. The best account of this manner of progression of fowls is given by Alfonso Borellus, in his treatise De Motu Animalium; and in the Religious Philosopher we have Borelli's doctrine stripped pretty much of its mathematical form. The posterior extremities are situated so far back, as to make us at first think they would be in continual hazard of falling down forwards when they walk; but this is prevented by their holding up their heads and neck, so as to make the centre of gravity fall upon the feet; and when they have occasion for climbing up a steep place, they stretch out their heads and necks forward, especially if they are short-legged, the better to preserve properly the balance of the body. Thus we may observe a goose entering a barn-door, where generally there is an ascending step, to stretch out its neck, which before was raised, and incline its body forwards. This is laughed at by the common people, who ascribe it to a piece of folly in the goose, as if afraid of knocking its head against the top of the door.

Carnivorous animals are provided with strong crooks. A peculiar claw for the catching their prey; water-fowls use them for swimming; and, principally for this purpose, fowls have a strong firm membrane interposed betwixt the toes. There is a beautiful mechanism to be observed in the toes of fowls, which is of considerable use to them. For their toes are naturally drawn together, or bended, when the foot is bended; this is owing to the shortness of the tendons of the toes, which pass over them, which is analogous to our heel; and that the toes are set in the circumference of a circle, as our fingers are: Hence, when the foot is bended, the tendons must consequently be much stretched; and, since they are inserted into the toes, must of necessity bend them when the foot is bended; and when the foot is extended, the flexors of the toes are again relaxed, and they therefore expanded. This is also of great use to different kinds of fowls; thus the hawk descending with his legs and feet extended, spreads his talons over his prey; and the weight of his body bending his feet, the toes are contracted, and the prey is seized by the talons. This is also of great use to water-fowls: for had there been no such contrivance as this, they must have lost as much time when they pulled their legs in as they had gained by the former stroke; but, as the parts are now framed, whenever the creature draws in its foot, the toes are at the same time bended and contracted into less space, so that the resistance made against the water is not near so great as before; on the contrary, when they stretch their foot, their toes are extended, the membrane betwixt them expanded, and consequently a greater resistance made to the water. Again, such fowls as live mostly in the air, or have occasion to sustain themselves on branches of trees in windy weather, and even in the night-time when asleep, while all their muscles are supposed to be in a state of relaxation; such have no more to do but lean down the weight of their bodies, and their toes continue bended without any muscles being in action; and whenever they would disentangle themselves, they raise up their bodies, by which their feet, and consequently their toes, are extended.

The rostrum, bill, or beak of fowls, is composed of the two mandibles; and, as in quadrupeds, the upper one in the beaks has no motion but what it possesses in common with the head. But parrots are an exception to this rule; for they can move the upper mandible at pleasure; this is exceeding convenient, as it enables them to lay hold of whatever comes in their way. Carnivorous fowls... Of fowls. fowls have their beaks long, sharp, and crooked; the domestic fowls, such as the hen-kind, &c. have strong short beaks, commodiously fitted to dig up and break their food; the water-fowl, again, have long or very broad scoop-like beaks, which is most convenient for them. The sternum of fowls is much larger proportionally than the human, and has a ridge rising in its middle for the more commodious origin of the muscles that move the wings. It is also less moveable than ours; for had it been very moveable, a great deal of the force employed for moving the wings would at every contraction of the muscles have been lost, or else some other muscles must have come into play to keep firm the sternum; but this additional weight would have been inconvenient for their progression.

What other things are most remarkable in the structure of the several viscera, we shall consider in that common domestic animal the cock or hen, and afterwards observe the difference of their viscera chylopoietica from a carnivorous fowl.

Sect. II. Anatomy of the Domestic Cock.

Though this kind of birds live upon food somewhat similar to that of man, yet as they have no teeth to separate or break down this food, we would expect to find something to compensate for the want of teeth, something remarkable in the organs of digestion: we shall therefore begin with these parts.

The oesophagus of this creature runs down its neck, somewhat inclined to the right side; and terminates in a pretty large membranous sac, which is the ingluvies or crop, where the food is macerated and dissolved by a liquor separated by the glands, which are easily observed everywhere on the internal surface of this bag.

The effect of this maceration may be very well observed in pigeons, who are sometimes in danger of being suffocated by the pease, &c. they feed upon, swelling to such an immense bulk in their ingluvies, that they can neither get upwards nor downwards. If it be a favourite fowl, it might be preserved by opening the sac, taking out the pease, and sewing up the wound.

The food getting out of this sac goes down by the remaining part of the oesophagus into the ventriculus succenturiatus seu infundibulum Peyeri, which is a continuation of the gullet with more numerous glands, which separate a liquor to dilute the food still more, which at length gets into the true stomach or gizzard, ventriculus callus, which consists of two very strong muscles covered externally with a tendinous aponeurosis, and lined on the inside by a very thick firm membrane, which we evidently discover to be a production of the cuticle. This might have been proved in some measure a priori, from taking notice, that this membrane, which in chicks is only a thin slight pellicle, by degrees turns thicker and stronger the more attrition it suffers: but there is no other animal-substance, so far as we know, which grows more hard and thick by being subjected to attrition, excepting the cuticle.—Hence may be drawn some kind of proof of what has been affirmed concerning the tunica vellosa of the stomach and intestines in the human body, viz. that it was in part a continuation of the epidermis; nay, all the hollow parts of the body, even arteries, veins, &c. seem to be lined with a production of this membrane, or one analogous to it. The use of the internal coat

of the stomach of fowls is to defend the more tender parts of that viscus from the hard grains and little stones those creatures take down. The use of the gizzard is to compensate for the want of teeth; and it is well fitted for this purpose from the great strength it possesses.

The digestion of these animals is performed merely by attrition, as is evinced by many experiments; and it is further assisted by the hard bodies they swallow. We see them daily take down considerable numbers of the most solid rugged little stones they find; and these can serve for no other purpose than to help the trituration of their aliments. After these pebbles, by becoming smooth, are unfit for this office, they are thrown up by the mouth. Hence fowls that are long confined, though ever so well fed, turn lean for want of these stones to help their digestion. This was put beyond all dispute by Mr. Taurry, who gave a species of metal to an ostrich, convex on one side and concave on the other, but carved on both; and opening the creature's body some time after, it was found, that the carving on the convex side was all obliterated, while the engraved character remained the same as before on the concave side, which was not subjected to the stomach's pressure: which could not have happened had digestion been performed by a menstruum, or any other way whatsoever; but may be easily solved by allowing a simple mechanical pressure to take place. We are, however, by no means to conclude from this, as some have too rashly done, that in the human body digestion is performed by simple attrition; otherwise we may, with equal strength of reason, by as good arguments drawn from what is observed in fishes, prove that the aliments are dissolved in our stomachs by the action of a menstruum. But this method of reasoning is very faulty; nor can it ever bring us to the true solution of any philosophical or medical problem. It is very plain, since the structure of the parts of the human stomach are so very different from that of this creature, that it is foolish and unreasonable to imagine both of them capable of producing the same effects. At each end of the stomach, there are as it were two particular sacs of a different texture from the rest of the stomach, not consisting of strong muscular fibres; they seem to be receptacles for the stones (especially at the end which is farthest from the orifice), while the digested aliment is protruded into the intestines.

Spallanzani, however, has lately found, that pebbles are not at all necessary to the trituration of the food of these animals. At the same time, he does not deny, that when put in motion by the gastric muscles, they are capable of producing some effect on the contents of the stomach; but is inclined to believe, that they are not sought for and selected by design, as many suppose, but because they frequently happen to be mixed with the food.

The duodenum begins pretty near the same place at Duodenum which the oesophagus enters; yet notwithstanding the vicinity of these two tubes, the aliments are in no danger of getting out before they are perfectly digested, by reason of a protuberance, or septum medium, betwixt the orifices; and in those creatures who have such a strong muscular stomach, it is a matter of great indifference whether the entry of the oesophagus or pylorus be be highest, provided that the entry from the oesophagus does not allow the food to regurgitate, since the force of the stomach can easily protrude it towards the duodenum. This gut is mostly in the right side, and hangs pendulous in their abdomen, having its two extremities fixed to the liver. The ductus choledochus enters near its termination, where it mounts up again to be fixed to the liver; and left, by the contraction of the intestines, the bile should pass over without being intimately blended with the chyle, that duct enters downwards, contrary to the course of the food, and contrary to what is observed in any of the animals we have yet mentioned. But still the general intention is kept in view, in allowing these juices the fairest chance of being intimately blended with the food.

The small guts are proportionally longer than those of carnivorous birds, for the general cause already assigned. At the end of the ilium they have two large intestina ceca, one on each side, four or five inches long, coming off from the side of the rectum, and ascending; and we find them containing part of the food: These serve as reservoirs to the feces; which, after some remora, there regurgitate into what soon becomes the rectum; which, together with the excretories of urine and organs of generation, empties itself into the common cloaca. The small intestines are connected by a long loose mesentery, which has little or no fat accompanying the blood-vessels, there being no hazard of the blood's being stopped.

The pancreas in the creature lies betwixt the two folds of the duodenum, and sends two or three ducts into this gut pretty near the biliary.

The spleen. The spleen is here of a round globular figure, situated between the liver and stomach; and betwixt these and the back-bone it enjoys the same properties as in other animals, viz. large blood-vessels, &c. All its blood is sent into the vena portarum, and has a perpetual conglutination. It has no excretory, as far as we know. Their liver is divided into two equal lobes by a pellucid membrane, running according to the length of their body: and hence we may observe, that it is not proper to that bowel to lie on the right side; which is still more confirmed by what we observe in fishes, where the greatest part of it lies in the left side.

The shape of their gall-bladder is not much different from that of quadrupeds; but is thought to be longer in proportion to the size of the animal, and is farther removed from the liver.

The principal difference to be remarked in their heart, is the want of the valvula tricuspides, and their place being supplied by one fleshy flap.

The lungs are not loose within the cavity of the thorax, but fixed to the bone all the way; neither are they divided into lobes, as in those animals that have a large motion in their spine. They are two red spongy bodies, covered with a membrane that is pervious, and which communicates with the large vesicles or air-bags that are dispersed over their whole abdomen; which vesicles, according to Dr Monro, serve two very considerable uses. The one is to render their bodies specifically light, when they have a mind to ascend and buoy themselves up when flying, by diffusing their lungs with air, and also straighten their trachea arteria, and so return the air. Secondly, they supply the place of a muscular diaphragm and strong abdominal muscles; producing the same effects on the several contained visceræ, as these muscles would have done, without the inconveniency of their additional weight; and conducing as much to the exclusion of the egg and feces.

Dr Hunter hath lately made some curious discoveries relative to these internal receptacles of air in the bodies of birds. Some of them are lodged in the fleshy parts, and some in the hollow bones; but all of them communicate with the lungs. He informs us, that the air-cells which are found in the soft parts have no communication with the cellular membrane which is common to birds as well as other animals. Some of them communicate immediately with each other; but all of them by the intervention of the lungs as a common centre. Some of them are placed in cavities, as the abdomen; others in the interstices of parts, as about the breast. The bones which receive air are of two kinds; some of them divided into innumerable cells; others hollowed out into one large canal. They may be distinguished from such as do not receive air, by having less specific gravity; by being less vascular; by containing little oil; by having no marrow nor blood in their cells; by having less hardness and firmness than others; and by the passage for the air being perceivable.

The mechanism by which the lungs are fitted for conveying air to these cavities is, their being attached to the diaphragm, and connected also to the ribs and sides of the vertebrae. The diaphragm is perforated in several places by pretty large holes, allowing a free passage of air into the abdomen. To each of these holes is attached a distinct membranous bag, thin and transparent. The lungs open at their anterior part into membranous cells, which lie upon the sides of the pericardium, and communicate with the cells of the sternum. The superior parts of the lungs open into cells of a loose net-work, through which the trachea and oesophagus pass. When these cells are distended with air, it indicates passion, as in the case of the turkey-cock, pouting-pigeon, &c.

These cells communicate with others in the axilla, and under the large pectoral muscle; and those with the cavity of the os humeri, by means of small openings in the hollow surface near the head of that bone. Lastly, The posterior edges of the lungs have openings into the cells of the vertebrae, ribs, os sacrum, and other bones of the pelvis, from which the air finds a passage to the cavity of the thigh-bone.

Concerning the use of these cavities the doctor conjectures, that they are a kind of appendage to the lungs; and that, like the bags continued through the bellies of amphibious animals, they serve as a kind of reservoirs of air. They assist birds during their flight, which must be apt to render frequent respiration difficult. He farther inferrates, that this construction of the organs of respiration may assist birds in singing; which, he thinks, may be inferred from the long continuance of long between the breathings of a canary-bird. On tying the trachea of a cock, the animal breathed through a canula introduced into his belly; another through the os humeri, when cut across; and a hawk through the os femoris. In all these cases the animals soon died. In the first, the doctor attributes the death to an inflammation of the bowels; but in the last, he owns it was owing to difficult breathing. What took place, however, was sufficient to show that the animals really did breathe through the bone.

When we examine the upper end of the trachea, we observe a rima glottidis with muscular sides, which may act in preventing the food or drink from passing into the lungs; for there is no epiglottis as in man and quadrupeds.

The trachea arteria, near where it divides, is very much contracted; and their voice is principally owing to this coarctation. If you listen attentively to a cock crowing, you will be sensible that the noise does not proceed from the throat, but deeper; nay, this very pipe, when taken out of the body, and cut off a little after its division, and blown into, will make a squeaking noise, something like the voice of these creatures. On each side, a little higher than this contraction, there is a muscle arising from their sternum, which dilates the trachea. The cartilages, of which the pipe is composed in this animal, go quite round it; whereas in men and quadrupeds they are discontinued for about one-fourth on the back-part, and the intermediate space is filled up by a membrane. Neither is the trachea so firmly attached to their vertebrae as in the other creatures we have examined. This structure we shall find of great service to them, if we consider, that had the same structure obtained in them as in us, their breath would have been in hazard of being stopped at every flexion or twisting of their neck, which they are frequently obliged to. This we may be sensible of by bending our necks considerably on one side, upon which we shall find a great strain and difficulty of breathing; whereas their trachea is better fitted for following the flexions of the neck by its loose connection to the vertebrae.

In place of a muscular diaphragm, this creature has nothing but a thin membrane connected to the pericardium, which separates the thorax and abdomen. But besides this, the whole abdomen and thorax are divided by a longitudinal membrane or mediastinum connected to the lungs, pericardium, liver, stomach, and to the fat lying over their stomach and guts, which is analogous to an omentum, and supplies its place.

The lymphatic system in birds consists, as in man, of lacteal and lymphatic vessels, with the thoracic duct.

The lacteals indeed, in the strictest sense, are the lymphatics of the intestines; and, like the other lymphatics, carry only a transparent lymph; and instead of one thoracic duct, there are two, which go to the jugular veins. In these circumstances, it would seem that birds differ from the human subject, so far at least as we may judge from the dissection of a goose, the common subject of this inquiry, and from which the following description is taken.

The lacteals run from the intestines upon the mesenteric vessels: those of the duodenum pass by the side of the pancreas; afterward they get upon the celiac artery, of which the superior mesenteric is a branch. Here they are joined by the lymphatics of the liver, and then they form a plexus which surrounds the celiac artery. Here also they receive a lymphatic from the gizzard, and soon after another from the lower part of the esophagus. At the root of the celiac artery they are joined by the lymphatics from the glandula renalis, and near the same part by the lacteals from the other small intestines, which vessels accompany the lower mesenteric artery; but, before they join those from the duodenum, receive from the rectum a lymphatic, which runs from the blood-vessels of that gut. Into this lymphatic some small vessels from the kidneys seem to enter at the root of the celiac artery. The lymphatics of the lower extremities probably join those from the intestines. At the root of the celiac artery and contiguous part of the aorta, a net-work is formed by the vessels above described. From this net-work arise two thoracic ducts, of which one lies on each side of the spine, and runs obliquely over the lungs to the jugular vein, into the inside of which it terminates, nearly opposite to the angle formed by the vein and this subclavian one. The thoracic duct of the left side is joined by a large lymphatic, which runs upon the esophagus. The thoracic ducts are joined by the lymphatics of the neck, and probably by those of the wings where they open into the jugular veins. The lymphatics of the neck generally consist of two large branches, on each side of the neck, accompanying the blood-vessels; and these two branches join near the lower part of the neck, and form a trunk which runs close to the jugular vein, and opens into a lymphatic gland; from the opposite side of this gland a lymphatic comes out, which ends in the jugular vein.

On the left side, the whole of this lymphatic joins the thoracic duct of the same side; but, on the right one, part of it goes into the inside of the jugular vein a little above the angle; whilst another joins the thoracic duct, and with that duct forms a common trunk, which opens into the inside of the jugular vein, a little below the angle which that vein makes with the subclavian. This system in birds differs most from that of quadrupeds, in the chyle being transparent and colourless, and in there being no visible lymphatic glands, neither in the course of the lacteals, nor in that of the lymphatics of the abdomen, nor near the thoracic ducts.

The kidneys lie in the hollow excavated in the side Kidneys of the back-bone, from which there is sent out a bluish-coloured canal running along by the side of the vas deferens, and terminating directly in the common cloaca. This is the ureter, which opens by a peculiar aperture of its own, and not at the penis. Fowls having no vesica urinaria, it was thought by some they never passed any urine, but that it went to the nourishment of the feathers: but this is false; for that whitish substance that you see their greenish faeces covered with, and which turns afterwards chalky, is their urine. Let us next consider the organs of generation of both sexes, and first those of the male.

The testicles are situated one on each side of the back-bone; and are proportionally very large to the creature's bulk. From these run out the vasa seminalia; the organs of generation in the male. These run straight; but after they recede farther from the body of the testicle, they acquire an undulated or convoluted form, as the epididymis in man. These convolutions partly supply the want of vesicule seminalis, their coition being at the same time very short: They terminate in the penis, of which the cock has two, one on each side of the common cloaca, pointing directly outwards. They open at a distance from each other, and are very small and short; whence they have escaped the notice of anatomists, who have often denied their existence. In birds there is no pro- slate gland. This is what is chiefly remarkable in the organs of the male.

The *roccmus vitellorum*, being analogous to the ovaria in the human subject, are attached by a proper membrane to the back-bone. This is very fine and thin, and continued down to the uterus. Its orifice is averse with respect to the ovaria; yet notwithstanding, by the force of the *orgajmus venereus*, it turns round and grasps the *vitellus*, which in its passage through this duct, called the *infundibulum*, receives a thick glutinous liquor, secreted by certain glands. This, with what it receives in the uterus, composes the white of the egg. By this tube then it is carried into the uterus. The shell is lined with a membrane; and in the large end there is a bag full of air, from which there is no outlet.

The uterus is a large bag, placed at the end of the *infundibulum*, full of wrinkles on its inside; here the egg is completed, receiving its last involucrum, and is at last pushed out at an opening on the side of the common cloaca. From the testes in the male being so very large in proportion to the body of the creature, there must necessarily be a great quantity of semen concerned; hence the animal is falacious, and becomes capable of impregnating many females. The want of the *vesicula seminalis* is in some measure supplied by the convolutions of the *vasa deferentia*, and by the small distance betwixt the secreting and excretory organs.

The two *feminae* contribute also very much to their short coition; at which time the opening of the uterus into the cloaca is very much dilated, that the effect of the semen on the vitelli may be the greater.

A hen will of herself indeed lay eggs; but these are not impregnated, and yet appear entirely complete, except that the small black spot, which comes afterwards to be the rudiments of the chick, is not here to be observed.

After having observed the contents of the abdomen and thorax, we next proceed to examine the parts about the neck and head.

These creatures, as was observed of fowls in general, have no teeth. Some, indeed, have an appearance of teeth; but these are only small processes or *ferrae* rising out from the mandible, without any socket, &c. which would have been needless, as they swallow their food entire. But their *tongue* is made pretty firm, lest it should be hurt by the sharp points of the grain they feed on. It is of a triangular figure, and pointed before; and as by their depending posture their meat is in hazard of falling out of their mouths, to prevent this there are several small pointed papillae standing out upon their tongue and palate, with their points inclined backwards, allowing an easy passage to the food, but hindering it to return.

We have here no *nervum palatinum*, *uvula*, or *epiglotis*; and in place of two large holes opening into the nose, there is only a long narrow rima supplied with pretty strong muscles, and such another supplies the place of a glottis. The creature has a power of shutting both at pleasure; and the nature of their food seems not only to exempt them from the hazard of its getting into the nose or trachea, but its sharp points would hurt an uvula, or epiglottis, if they had any.

Hence we see with what difficulty they swallow dough or other sort of food that can be easily moulded into any form. When we examine the upper end of the trachea, we observe a rima glottidis with muscular fibres, which may act in preventing the food or drink from passing into the lungs, for there is no epiglottis as in man and quadrupeds.

Their *cranium* is more cellular and cavernous than ours. By this means their heads are light, yet strong enough to resist external injuries; for the enlarging the diameter of bones contributes to their strength. By this cavernous cranium the organ of smelling is supposed to be considerably enlarged; and further, singing birds, as is observed by Mr Ray and Mr Derham, have this cavernous structure of the brain still more observable: and we are told that the cavity of the tympanum communicates with the cells; but this seems rather founded on theory than matter of fact. Their brain is covered with the common membranes, but its external surface is not formed into so many gyrae or convolutions as ours. Its anterior part is quite solid, of a cineritious colour, and so far has a resemblance of the *corpora striata* as to give rise to the olfactory nerves. The whole of it appears to us as imperfect, and we can scarce determine whether there be anything analogous to a third or fourth ventricle: neither the *corpus callosum*, *fornix*, *nates*, or *teles*, &c. can be observed here; which parts therefore cannot be imagined as absolutely necessary for the functions of life, since we find these creatures perform them sufficiently well. We may perhaps think these serve a particular use in man, who is a rational creature; but then quadrupeds enjoy them in common with men. These protuberances, &c. seem rather to depend on the different disposition of the several parts, being variously connected and meeting in different directions in different places, than their being absolutely necessary for any particular use; and the uses that have been assigned to different parts of the brain by authors, seem to have no foundation but in the author's fancy.

Their organ of *smelling* is very large, and well provided with nerves; hence they have this sensation very acute. Ravens and other birds of prey give a striking proof of this, by their being able to find out their prey, though concealed from their sight and at a considerable distance.

Those birds that grope for their food in the waters, mud, &c. have large nerves, which run quite to the end of their bills, by which they find out and distinguish their food.

The anterior part of their *eyes* (instead of having the sclerotic coat continued, so as to make near a sphere as in us) turns all of a sudden flat; so that here the sclerotic makes but half a sphere; and the cornea rises up afterwards, being a portion of a very small and distinct sphere; so that in these creatures there is a much greater difference betwixt the sclerotic and cornua than in us. Hence their eyes do not jut out of their heads, as in man and quadrupeds. As most of these creatures are continually employed in hedges and thickets, therefore, that their eyes might be secured from these injuries, as well as from too much light when flying in the face of the sun, there is a very elegant mechanism in their eyes. A membrane rises from the internal canthus, Of Fowls, thus, which at pleasure, like a curtain, can be made to cover the whole eye; and this by means of a proper muscle that rises from the sclerotic coat, and passing round the optic nerves, runs through the myciculus oculi attollens (by which however the optic nerves are not compressed) and palpebra, to be inserted into the edge of this membrane. Whenever this muscle ceases to act, the membrane by its own elasticity again discovers the eye. This covering is neither pellucid nor opaque, both which would have been equally inconvenient; but, being somewhat transparent, allows as many rays to enter as to make any object just visible, and is sufficient to direct them in their progression. By means of this membrane it is that the eagle is said to look at the sun. Quadrupeds also, as we mentioned before, have a small membrana nictitans.

Besides, all fowls have another particularity, the use of which is not so well understood; and that is, a pretty long black triangular purse, rising from the bottom of their eye just at the entry of the optic nerve, and stretched out into their vitreous humour, and one would imagine it gave some threads to the crystalline. To this the French (who probably were the first who took notice of it in their dissections before the Royal Academy) gave the name of bourge noire. This may possibly serve to suffocate some of the rays of light, that they may see objects more distinctly without hurting their eyes. It has a connection with the vitreous, and seems to be joined also to the crystalline humours. If we suppose it to have a power of contraction (which may be as well allowed as that of the iris), it may so alter the position of the vitreous and crystalline humours, that the rays from any body may not fall perpendicularly upon the crystalline; and this seems to be necessary in them, since they cannot change the figure of the anterior part of their eye so much as we can do: and as this animal is exposed often to too great a number of rays of light, so they have no tapetum, but have the bottom of their eye wholly black on the retina; and in consequence of this, fowls see very ill in the dark.

They have no external ear; but in place thereof a tuft of very fine feathers covering the meatus auditorius, which easily allows the rays of sound to pass them, and likewise prevents dust or any insect from getting in. An external ear would have been inconvenient in their passing through thickets, and in flying, &c. A liquor is separated in the external part of the ear, or meatus auditorius, to lubricate the passage, and further prevent the entrance of any insects, &c. The membrana tympani is convex externally; and no muscles are fixed to the bones of their ear, which are rather of a cartilaginous consistence: any tremulous motions impressed on the air are communicated in these creatures merely by the spring and elasticity of these bones; so, probably, the membrane is not so stretched as in the human ear by muscles. The semicircular canals are very distinct, and easily prepared.

Sect. III. Anatomy of a Carnivorous Bird.

We come next to the birds of prey, and for an example shall take a stannel or small hawk. The principal difference to be observed in them, is in their chylopoietic viscera, which may be accounted for from their different way of life.

Immediately under their clavicles, you will observe the oesophagus expanded into their ingluvies, which is proportionally less than in the granivorous kind, since their food does not swell so much by maceration; and for the same reason, there is a less quantity of a menstruum to be found here.

They have also a ventriculus succenturiatus, plentifully stored with glands, situated immediately above their succenturiated stomach, which we see here is thin and musculo-membranous, otherwise than in the granivorous kind; and this difference, which is almost the only one we shall find betwixt the two different species of fowls, is easily accounted for from the nature of their food, which requires less attrition, being easier of digestion than that of the other kind; nevertheless, it seems requisite it should be stronger than the human, to compensate the want of abdominal muscles, which are here very thin.

The same mechanism obtains in this creature's duo-intestina, denum that we have hitherto observed. As being a carnivorous animal, its guts are proportionally shorter than those of the granivorous kind; for the reason first given, viz. its food being more liable to corrupt, therefore not proper to be long detained in the body; and for that reason it has no intestina ceca, of which the other species of fowls have a pair. The difference in their wings, backs, and claws, are obvious; and have been already in some measure observed.

Chap. III. The Anatomy of Aqueous Animals.

Sect. I. Of the Amphibious Tribe.

Aqueous animals are generally divided into such as have lungs, and such as want them. The first species differ so considerably from an ox or any other quadruped, that a few observations may be sufficient to give an idea of their internal structure; for this purpose, we shall first examine that species of them which most resembles man in the internal structure, the tortoise.

1. Tortoise. The covering of this animal is composed of a shell so remarkably hard and firm in its texture, that a loaded waggon may go over it without hurting the shell or the animal within it. In the young animal, this shell grows harder in proportion as its contents expand; and this creature never changes its shell as some others do; hence it was necessary for it to be made up of different pieces; and these are more or less distinct in different animals. Their feet are small and weak; and they are exceedingly slow in motion.

It has neither tongue nor teeth; to make up for which, their lips are so hard as to be able to break almost the hardest bodies.

The alimentary canal very much resembles that of the former clasps.

The principal difference is in the circulation of the blood. The heart has two distinct auricles, without any communication; and under these, there is the appearance of two ventricles similar in shape to those of the former clasps; but they may be considered as one cavity; for the ventricle sends out not only the pulmonary artery, but likewise the aorta; for there is a passage in the septum, by which the ventricles communicate freely, and the blood passes from the left into... Of Aqueous into the right one. From the aorta the blood returns into the right auricle, while that from the pulmonary artery returns to the left auricle, from which it is sent to the left ventricle, &c., so that only a part of the blood is sent to the lungs, the rest going immediately into the aorta; hence the animal is not under the necessity of breathing so often as otherwise it would be.

From the base of the right ventricle goes out the pulmonary artery and aorta. The pulmonary artery is spent upon the lungs. The aorta may be said to be three in number: for the aorta sinistra ascends through the pericardium in company with the pulmonary artery; and afterwards turns down, and sends off a considerable branch, which splits into two; one of which joins the right aorta, while the other is distributed upon the liver, stomach, intestines, &c. What remains of this aorta runs to the kidneys or posterior extremities of that side. An aorta descendens, &c., after piercing the pericardium, runs down and communicates with the branch already mentioned, is distributed upon the right kidney and inferior extremity, and also upon the bladder and parts of generation. An aorta ascendens, after getting out of the pericardium, supplies the fore-legs, neck, and head. The blood in the superior part of the body returns to the right auricle by two jugular veins, which unite after perforating the pericardium. From the inferior part, it returns to the same auricle by two large veins; one on the right side receives the blood in the right lobe of the liver; the other on the left side receives the blood in the left lobe, and also a trunk which corresponds with the inferior vena cava in other animals. The pulmonary vessels run in the left auricle in the common way.

The absorbent system in the turtle, like that in the former class, consists of lacteals and lymphatics, with their common trunks the thoracic ducts; but differs from it in having no obvious lymphatic glands on any part of its body, nor plexus formed at the termination in the red veins.

The lacteals accompany the blood-vessels upon the mesentery, and form frequent net-works across these vessels; near the root of the mesentery a plexus is formed, which communicates with the lymphatics coming from the kidneys and parts near the anus. At the root of the mesentery on the left side of the spine, the lymphatics of the spleen join the lacteals; and immediately above this a plexus is formed, which lies upon the right aorta. From this plexus a large branch arises, which passes behind the right aorta to the left side, and gets before the left aorta, where it affixes in forming a very large receptaculum, which lies upon that artery.

From this receptaculum arise the thoracic ducts. From its right side goes one trunk, which is joined by that large branch that came from the plexus to the left side of the right aorta, and then passes over the spine. This trunk is the thoracic duct of the right side; for having got to the right side of the spine, it runs upwards, on the inside of the right aorta, towards the right subclavian vein; and when it has advanced a little above the lungs, it divides into branches, which near the same place are joined by a large branch, that comes up on the outside of the aorta. From this part upwards, those vessels divide and subdivide, and are afterwards joined by the lymphatics of the neck, which likewise form branches before they join those from below. So that between the thoracic duct and the lymphatics of the same side of the neck, a very intricate network is formed; from which a branch goes into the angle between the jugular vein and the lower part or trunk of the subclavian. This branch lies therefore on the inside of the jugular vein, whilst another gets to the outside of it, and seems to terminate in it, a little above the angle, between that vein and the subclavian.

Into the above mentioned receptaculum the lymphatics of the stomach and duodenum likewise enter. Those of the duodenum run by the side of the pancreas, and probably receive its lymphatics and a part of those of the liver. The lymphatics of the stomach and duodenum have very numerous anastomoses, and form a beautiful network on the artery which they accompany. From this receptaculum likewise (besides the trunk already mentioned, which goes to the right side) arise two other trunks pretty equal in size; one of which runs upon the left side, and the other upon the right side of the left aorta, till they come within two or three inches of the left subclavian vein; where they join behind the aorta, and form a number of branches which are afterwards joined by the lymphatics of the left side of the neck; so that here a plexus is formed as upon the right side. From this plexus a branch issues, which opens into the angle between the jugular and subclavian vein.

2. Serpent and Crocodile. The circulation in these is similar to that of the turtle; but we find only one ventricle. The blood goes from the right auricle to the ventricle which sends out the pulmonary artery and aorta; the blood from the pulmonary artery returns to the left auricle, that from the aorta going to the right auricle, and both the auricles opening into the ventricle.

3. Frog and Lizard. These differ from the former animals, in having only one auricle and a ventricle; and besides, the ventricle sends out a single artery, which afterwards splits into two parts; one to supply the lungs, the other runs to all the rest of the body; from the lungs and from the other parts, the blood returns into the auricle.

Sect. II. Anatomy of Fishes.

Of these we may first observe, that they have a very strong thick cuticle, covered with a great number of scales, laid one on another like the tiles of houses. This among other arguments is supposed to prove the human epidermis to be of a squamous structure: but the scales resemble the hairs, wool, feathers, &c., of the creatures that live in air; and below these we observe their proper cuticle and cutis.

The generality of fishes, particularly those shaped like the cod, haddock, &c., have a line running on each side. These lines open externally by a number of ducts, which throw out a mucous or slimy substance that keeps them soft and clammy, and seems to serve the same purpose with the mucous glands or ducts which are placed within many of our internal organs.

In the next place, these creatures have neither anterior nor posterior extremities, as quadrupeds and fowls; for their progression is performed in a different way, fins, tail, swimming, fins, tail, sir, from bags, &c. from either of those species of animals; for this purpose they are provided with machines, properly consisting of a great number of elastic beams, connected to one another by firm membranes, and with a tail of the same texture; their spine is very moveable towards the posterior part, and the strongest muscles of their bodies are inserted there. Their tails are so framed as to contract to a narrow space when drawn together to either side, and to expand again when drawn to a straight line with their bodies; so, by the assistance of this broad tail, and the fins on their sides, they make their progression much in the same way as a boat with oars on its sides and rudder at stern. The perpendicular fins situated on the superior part of their body keep them in equilibrio, hindering the belly from turning uppermost; which it would readily do, because of the air bag in the abdomen rendering their belly specifically lighter than their back; but by the resistance these fins meet with when inclined to either side, they are kept with their backs always uppermost.

The best account of this matter, we have in the treatise before mentioned, viz., Borellius de Motu Animalium, cap. 23.

It may be next observed, that these creatures have nothing that can be called a neck, seeing they seek their food in an horizontal way, and can move their bodies either upwards or downwards, as they have occasion, by the contraction or dilatation of the air-bag; a long neck, as it would hinder their progression, would be very disadvantageous in the element they live in.

The abdomen is covered on the inferior part with a black-coloured thin membrane resembling our peritoneum. It is divided from the thorax by a thin membranous partition, which has no muscular appearance; so that we have now seen two different sorts of animals that have no muscular diaphragm.

These creatures are not provided with teeth proper for breaking their aliment into small morsels, as the food they use is generally small fishes, or other animals that need no trituration in the mouth, but spontaneously and gradually dissolve into a liquid chyle. Their teeth serve to grasp their prey, and hinder the creatures they have once caught from escaping again. For the same purpose, the internal cartilaginous basis of the bronchi, and the two round bodies situated in the posterior part of the jaws, have a great number of tentacles fixed into them, in such a manner as that anything can easily get down, but is hindered from getting back. The water that is necessarily taken in along with their food in too great quantities to be received into their jaws in deglutition, passes between the interstices of the bronchi and the flap that covers them. The compression of the water on the bronchi is of considerable use to the creature, as we shall explain by and by.

The esophagus in these creatures is very short, and scarcely distinguished from their stomach, seeing their food lies almost equally in both. The stomach is of an oblong figure. There are commonly found small fishes in the stomach of large ones still retaining their natural form; but when touched, they melt down into a jelly. From this, and the great quantity of liquors poured into their stomachs, we may conclude, that digestion is solely brought about in them by the dissolving power of a menstruum, and that no trituration happens here.

The guts in these animals are very short, making only three turns; the last of which ends in the common cloaca for the feces, urine, and semen, situated about the middle of the inferior part of their bodies.

To what we call pancreas, some give the name of intestinula ceca; it consists of a very great number of small threads, like so many little worms, which all terminate at last in two larger canals that open into the first gut, and pour into it a viscid liquor much about the place where the biliary ducts enter. That kind of pancreas formed of intestinula ceca is peculiar to a certain kind of fishes; for the cartilaginous, broad, and flat kind, as the skate, sole, flounder, &c., have a pancreas resembling that of the former class of animals. Their intestines are connected to the back-bone by a membrane analogous to a mesentery.

Their liver is very large, of a whitish colour, and lies almost in the left side wholly, and contains a great deal bladder, of fat or oil.

The gall-bladder is situated a considerable way from their liver; and sends out a canal, the cystic duct, which joins with the hepatic duct just at the entry into the gut. Some fibres being observed stretched from the liver to the gall-bladder, but without any apparent cavity, the bile was supposed not to be carried into the gall-bladder in the usual way, but that it must either be secreted on the sides of the sac, or regurgitated into it from the canalis choledochus. It is certain, however, that hepato-cystic ducts exist in fishes as well as in fowls. This, for example, is very obvious in the salmon, where large and distinct ducts run from the biliary ducts of the liver, and open into the gall-bladder.

The spleen is placed near the back-bone, and at a place where it is subjected to an alternate pressure from the contraction and dilatation of the air-bag, which is situated in the neighbourhood. Since, in all the different animals we have dissected, we find the spleen attached to somewhat that may give it a conglobation; as in the human subject and quadrupeds, it is contiguous to the diaphragm; in fowls, it is placed between the back-bone, the liver, and stomach; in fishes, it lies on the fascia aëria; and since we find it so well served with blood-vessels, and all its blood returning into the liver; we must not conclude the spleen to be an innutile pondera, only to serve as a balance to the animal pro æquilibrio, but particularly designed for preparing the blood to the liver.

The only organs of generation in this animal are two organs of generation situated in the abdomen uniting near the podex. These in the male are filled with a whitish firm substance called the milk; and in the female with an infinite number of little ova cluttered together, of a reddish yellow colour, called the roe. Both these at spawning-time we find very much distended; whereas at another time the male organs can scarce be distinguished from the female; nor is there any proper instrument in the male for throwing the seed into the organs of the female, as in other creatures. We shall not take upon us to determine the way whereby the female sperm is impregnated; but we find that the spawn of frogs consists in the small specks wrapped up in a whitish glutinous liquor; these specks are the rudiments of the young frogs, which are nourished in that liquor till Of Aquaeus till they are able to go in search of their food. In the same way, the ova of fishes are thrown out and deposited in the sand, the male being for the most part ready to impregnate them, and they are incubated by the heat of the sun. It is curious enough to remark with what care they seek for a proper place to deposit their ova, by swimming to the shallow, where they can better enjoy the sun's rays, and thus the large jaws of other fishes. The river-fishes, again, spawn in some creek free from the hazard of the impetuous stream. But whether this mixture be brought about in fishes by a simple application of the genitals to each other, or if both of them throw out their liquors at the same time in one place, and thus bring about the desired mixture, it is not easy to determine. Spallanzani has found, that the eggs of frogs, toads, and water mews, are not fecundated in the body of the female; that the male emits his semen upon the spawn while it is flowing from the female; and that the fetus pre-exists in the body of the female: but whether impregnation takes place in the same manner in fishes, he has not yet been able to determine, though he seems to think it probable. These creatures are so shy, that we cannot easily get to observe their way of copulation, and are consequently but little acquainted with their natural history. Frogs, it is very evident, do not copulate; at least no farther than to allow both sexes an opportunity of throwing their sperm. Early in the spring the male is found for several days in close contact upon the back of the female, with his fore legs round her body in such a manner that makes it very difficult to separate them, but there is no communication. At this time the female lays her spawn in some place that is most secure, while the male emits his sperm upon the female spawn.

After raising up the black peritoneum in fishes, there comes in view an oblong white membranous bag, in which there is nothing contained but a quantity of elastic air. This is the swimming-bladder: it lies close to the back-bone; and has a pretty strong muscular coat, whereby it can contract itself. By contracting this bag, and condensing the air within it, they can make their bodies specifically heavier than water, and so readily fall to the bottom; whereas the muscular fibres ceasing to act, the air is again dilated, and they become specifically lighter than water, and to swim above. According to the different degrees of contraction and dilatation of this bladder, they can keep higher or lower in the water at pleasure. Hence flounders, soles, raia or skate, and such other fishes as want this sac, are found always groveling at the bottom of the water: it is owing to this that dead fishes (unless this membrane has been previously broke) are found swimming a-top, the muscular fibres then ceasing to act, and that with their bellies uppermost; for the backbone cannot yield, and the distended sac is protruded into the abdomen, and the back is consequently heavier at its upper part, according to their posture. There is here placed a glandular substance, containing a good quantity of red blood; and it is very probable that the air contained in the swimming bladder is derived from this substance. From the anterior part of the bag go out two processes or appendices, which, according to the gentlemen of the French academy, terminate in their sacs: In a variety of other fishes we find communications with some parts of the alimentary canal, particularly the esophagus and stomach. The salmon has an opening from the fore end of the air-bag into the esophagus, which is surrounded by a kind of muscular fibres. The herring has a funnel-like passage leading from the bottom of the stomach into the air-bag; but it is not determined whether the air enters the air-bag by this opening, or comes out by it: the latter, however, seems to be the more probable opinion, as the glandular body is found in all fishes, whereas there are several without this passage of communication.

At the superior part of this bag there are other red-coloured bodies of a glandular nature, which are connected with the kidneys. From them the ureters go down to their insertion in the vesica urinaria, which lies in the lower part of the abdomen; and the urethra is there produced, which terminates in the podex. These last-mentioned parts have not hitherto been observed in some species of fishes; whence authors too hastily denied them in all. These creatures have a membranous diaphragm, which forms a sac in which the heart is contained. It is very tense, and almost perpendicular to the vertebrae.

The heart is of a triangular form, with its base downwards, and its apex uppermost; which situation has but one it has because of the branchiae. It has but one auricle and one ventricle, because they want lungs; and one great artery. The size of the auricle and that of the ventricle are much the same; the artery sends out numberless branches to the branchiae or gills. And what is rather curious, this artery, instead of supporting all parts as in the frog, is distributed entirely upon the gills; every branch terminating there, and becoming so extremely small as at last to escape the naked eye.

The branchiae lie in two large slits at each side of their heads, and seem to be all they have that bears any analogy to lungs. Their form is semicircular; they have a vast number of red fibrillae standing out on each side of them like a fringe, and very much resemble the vane of a feather. These branchiae are perpetually subjected to an alternate motion and pressure from the water; and we may here remark, that we have not found any red blood but in places subjected to this alternate pressure. This observation will help us in explaining the action of the lungs upon the blood. Over these gills there is a large flap, allowing a communication externally; by which the water they are obliged to take into their mouths with their food finds an exit without passing into their stomach: it is owing to these flaps coming so far down that the heart is said commonly to be situated in their heads. The blood is collected again from the gills by a vast number of small veins, somewhat in the same manner as in our pulmonary vein; but instead of going back to the heart a second time, they immediately unite, and form an aorta descendens, without the intervention of an auricle and ventricle. Hence a young anatomist may be puzzled to find out the power by which the blood is propelled from the gills to the different parts of the body; but the difficulty will be considerably lessened when we consider the manner in which the blood is carried. carried through the liver from the intestines in man and quadrupeds. The aorta in fishes sends off branches which supply all the parts of the body excepting the gills. From the extremity of those branches the blood returns to the heart somewhat in the same manner as in the former class of animals; only there are two inferior veins cavae, whereas the former has but one.

Absorbent System in Fishes. We shall take the haddock as a general example; for the other fishes, particularly those of the same shape, will be found in general to agree with it.

On the middle of the belly of a haddock, immediately below the outer skin, a lymphatic vessel runs upwards from the anus, and receives branches from the parietes of the belly, and from the fin below the anus: near the head this lymphatic passes between the two pectoral fins; and having got above them, it receives their lymphatics. It then goes under the symphyse of the two bones which form the thorax, where it opens into a net-work of very large lymphatics, which lie close to the pericardium, and almost entirely surrounds the heart. This net-work, besides that part of it behind the heart, has a large lymphatic on each side, which receives lymphatics from the kidney, runs upon the bone of the thorax backwards; and when it has got as far as the middle of that bone, it sends off a large branch from its inside to join the thoracic duct. After detaching this branch, it is joined by the lymphatics of the thoracic fins, and soon after by a lymphatic which runs upon the side of the fish. It is formed of branches, which give it a beautiful penniform appearance.

Besides these branches, there is another set deeper which accompanies the ribs. After the large lymphatic has been joined by the above-mentioned vessels, it receives lymphatics from the gills, orbit, nose, and mouth. A little below the orbit, another net-work appears, consisting in part of the vessels above described, and of the thoracic duct. This net-work is very complete, some of its vessels lie on each side of the muscles of the gills; and from its internal part a trunk is sent out which terminates in the jugular vein.

The lacteals run on each side of the mesenteric arteries, anastomosing frequently across those vessels. The receptaculum into which they enter is very large, in proportion to them; and consists at its lower part of two branches, of which one lies between the duodenum and stomach, and runs a little way upon the pancreas, receiving the lymphatics of the liver, pancreas, of the lower part of the stomach, and the lacteals from the greatest part of the small intestines. The other branch of the receptaculum receives the lymphatics from the rest of the alimentary canal. The receptaculum formed by these two branches lies on the right side of the upper part of the stomach, and is joined by some lymphatics in that part, and also by some from the sound and gall-bladder, which in this fish adheres to the receptaculum. This thoracic duct takes its rise from the receptaculum, and lies on the right side of the oesophagus, receiving lymphatics from that part; and running up about half an inch, it divides into two ducts, one of which passes over the oesophagus to the left side, and the other goes straight upon the right side, passes by the upper part of the kidney, from which it receives some small branches, and soon afterwards is joined by a branch from the large lymphatic that lies above the bone of the thorax, as formerly mentioned: near this part it likewise sends off a branch to join the duct of the opposite side; and then, a little higher, is joined by those large lymphatics from the upper part of the gills, and from the fauces.

The thoracic duct, after being joined by these vessels, communicates with the net-work near the orbit, where its lymph is mixed with that of the lymphatics from the posterior part of the gills, and from the superior fins, belly, &c., and then from this net-work, a vessel goes into the jugular vein just below the orbit. This last vessel, which may be called the termination of the whole system, is very small in proportion to the net-work from which it rises; and indeed the lymphatics of the part are so large, as to exceed by far the size of the sanguiferous vessels.

The thoracic duct from the left side, having passed under the oesophagus from the right, runs on the inside of the vena cava of the left side, receives a branch from its fellow of the opposite side, and joins the large lymphatics which lie on the left side of the pericardium, and a part of those which lie behind the heart; and afterwards makes, together with the lymphatics from the gills, upper fins, and side of the fish, a net-work, from which a vessel passes into the jugular vein of this side. In a word, the lymphatics of the left side agree exactly with those of the right side above described. Another part of the system is deeper seated, lying between the roots of the spinal processes of the back-bone. This part consists of a large trunk that begins from the lower part of the fish, and as it ascends receives branches from the dorsal fins and adjacent parts of the body. It goes up near the head, and sends a branch to each thoracic duct near its origin.

The brain in fishes is formed pretty much in the Cerebrum, same way as that of fowls; only we may observe, that the posterior lobes bear a greater proportion to the anterior.

Their organ of smelling is large; and they have a power of contracting and dilating the entry into their smell, nose as they have occasion. It seems to be mostly by their acute smell that they discover their food; for their tongue seems not to have been designed for a very nice sensation, being of a pretty firm cartilaginous substance; and common experience evinces, that their sight is not of so much use to them as their smell in searching for their nourishment. If you throw a fresh worm into the water, a fish shall distinguish it at a considerable distance; and that this is not done by the eye, is plain from observing, that after the same worm has been a considerable time in the water and lost its smell, no fishes will come near it; but if you take out the bait, and make several little incisions into it, so as to let out more of the odoriferous effluvia, it shall have the same effect as formerly. Now it is certain, had the creatures discovered this bait with their eyes, they would have come equally to it in both cases. In consequence of their smell being the principal means they have of discovering their food, we may frequently observe their allowing themselves to be carried down with the stream, that they may ascend again leisurely against the current of the water; thus the odoriferous particles swimming in that medium, being Chap. III. Comparative Anatomy.

Of aqueous animals applied more forcibly to their smelling organs, produce a stronger sensation.

The optic nerves in these animals are not confounded with one another in their middle progress betwixt their origin and the orbit, but the one passes over the other without any communication; so that the nerve that comes from the left side of the brain goes distinctly to the right eye, and vice versa.

Indeed it would seem not to be necessary for the optic nerves of fishes to have the same kind of connection with each other as those of man have; for their eyes are not placed in the fore-part, but in the sides of their head; and of consequence, they cannot so conveniently look at any object with both eyes at the same time.

The lens crystallina is here a complete sphere, and more dense than in terrestrial animals, that the rays of light coming from water might be sufficiently refracted.

As fishes are continually exposed to injuries in the uncertain element they live in, and as they are in perpetual danger of becoming a prey to the larger ones, it was necessary that their eyes should never be shut; and as the cornea is sufficiently washed by the element they live in, they are not provided with palpebrae: but then, as in the current itself the eye must be exposed to several injuries, there was a necessity it should be sufficiently defended; which in effect it is by a firm pellucid membrane, that seems to be a continuation of the cuticle, being stretched over here. The epidermis is very proper for this purpose, as being inflexible and destitute of vessels, and consequently not liable to obstructions, or, by that means, of becoming opaque. In the eye of the skate tribe, there is a digitized curtain which hangs over the pupil, and may shut out the light when the animal rests, and it is similar to the tunica adnata of other animals.

Although it was formerly much doubted whether fishes possessed a sense of hearing, yet there can be little doubt of it now; since it is found that they have a complete organ of hearing as well as other animals, and likewise as the water in which they live is proved to be a good medium. Fishes, particularly those of the skate kind, have a bag at some distance behind the eyes, which contains a fluid and a soft cretaceous substance, and supplies the place of vestibule and cochlea. There is a nerve distributed upon it, similar to the portio mollis in man. They have three semicircular canals, which are filled with a fluid, and communicate with the bag: they have likewise, as the present professor of anatomy at Edinburgh has lately discovered, a meatus externus, which leads to the internal ear. The cod fish, and others of the same shape, have an organ of hearing somewhat similar to the former; but instead of a soft substance contained in the bag, there is a hard cretaceous stone. In this kind of fish no meatus externus has been yet observed: And Dr Monro is inclined to think that they really have not one. From the consideration that the common canal or vestibule, where the three semicircular canals communicate, is separated from the cavity of the cranium by a thin membrane only; that this cavity, in the greater number of fishes, contains a watery liquor in considerable quantity; and that, by the thinness of the cranium, the tremor excited by a porous body may readily and easily be transmitted through the cranium to the water within it, and so to the ear.

Chap. IV. The Anatomy of Insects.

As insects and worms are so exceedingly numerous, it would be endless to examine all the different kinds, nor would it serve any useful purpose to the anatomist. We shall therefore be content with making a few general observations, and these chiefly on the structure of their body; leaving the variety of their colour, shape, &c. to the naturalists. Insects differ from the former classes, by their bodies being covered with a hard crust or scales, by their having feelers or antennae arising from their head, and many of them breathing the air through lateral pores. As to the shape of their bodies, though it somewhat differs from that of birds, being in general not so sharp before to cut and make way through the air, yet it is well adapted to their manner of life. The base of their bodies is not formed of bone, as in many other animals, but the hard external covering serves them for skin and bone at the same time. Their feelers, beside the use of cleaning their eyes, are a guard to them in their walk or flight. Their legs and wings are well fitted for their intended service; but the latter vary so much in different insects, that from them naturalists have given names to the several orders of the class. As, first, the Coleoptera, or beetle tribe, which have a crustaceous elytra or shell, that shuts together, and forms a longitudinal suture down their back.

Hemiptera—as in cinex, cockroach, bug, &c., which have the upper wings half crustaceous and half membranaceous; not divided by a longitudinal suture, but incumbent on each other.

Lepidoptera—as the butterfly, have four wings, covered with fine scales in the form of powder.

Neuroptera—as the dragon-fly, spring-fly, &c., have four membranaceous transparent naked wings, generally reticulated.

Hymenoptera—as wasps, bees, &c., have four membranaceous wings, and a tail furnished with a sting.

Diptera—as the common house-fly, have only two wings.

Aptera—as the lobster, crab, scorpion, spider, &c., have no wings.

The structure of the eye in many insects is a most curious piece of mechanism. The outer part is remarkably hard, to guard against injuries; and has commonly a reticular appearance, or the whole may be looked upon as an assemblage of smaller eyes; but whether they see objects multiplied before them, has not yet been determined.

Linnaeus, and several others following him, deny the existence of a brain in these creatures. But it is certain, that at least a number of the larger kinds, as the lobster, crab, &c., have a soft substance similar to the brain, from which the optic and other nerves take their rise; besides, when this substance is irritated, the animal is thrown into convulsions: hence we would conclude, that insects have a brain as well as the former classes, although this is smaller in proportion to their bodies.

Their ear has been lately discovered to be placed at the root of their antennae or feelers, and can be... distinctly seen in some of the larger kinds, as the lobster.

They have a stomach, and other organs of digestion; and it is curious, that in some, as the lobster, the teeth are found in the stomach.

They have a heart and blood-vessels, and circulation is carried on in them somewhat as in the former clas; but the blood is without red globules; or, as naturalists speak, is colourless. In the lobster, and others of the larger kind, when a piece of the shell is broken, the pulsation of the heart is seen distinctly, and that sometimes for several hours after it has been laid bare.

Lungs. The existence of these by some has been denied. But late experiments and observations show, that no species want them, or at least something similar to them; and in many insects, they are larger in proportion than in other animals: in most of them they lie on or near the surface of their body; and send out lateral pores or trachea, by which, if the animal is besmeared with oil, it is instantly suffocated.

Generation. The same difference in sex exists in insects as in other animals, and they even appear more disposed to increase their species; many of them, when become perfect, seeming to be created for no other purpose but to propagate their like. Thus the silkworm, when it arrives at its perfect or moth-state, is incapable of eating, and can hardly fly; it endeavours only to propagate its species: after which the male immediately dies, and so does the female as soon as she has deposited her eggs.

Besides those of the male and female, a third sex exists in some insects, which we call neuter. As these have not the distinguishing parts of either sex, they may be considered as eunuchs or infertile. We know of no instance of this kind in any other class of animals; and it is only found among those insects which form themselves into societies, as bees, wasps, and ants: and here these eunuchs are real slaves, as on them lies the whole business of the economy. No hermaphrodites have as yet been discovered among insects.

Many have imagined that the generality of insects were merely the production of putrefaction, because they have been observed to arise from putrefied substances: but a contrary opinion is now more generally adopted; and it is pretty certain, that if putrid bodies be shut up in a close vessel, no insects are ever generated unless their ova have been originally deposited there. They are oviparous animals, and lay their eggs in places most convenient for the nourishment of their young; some in water, others in flesh; some in fruit and leaves; while others make nests in the earth or in wood, and sometimes even in the hardest stone. The eggs of all insects first become (larva) caterpillar or maggot; from which they are changed into (pupa) chrysalis or aurelia, so named from their being inclosed in a case; and these dying, or seeming to die, the (imagae) fly, or butterfly or perfect state, succeeds; and during each of these changes their appearance differs wonderfully.

Chap. V. Of Worms.

With respect to this class of animals, they have characters corresponding with those of the former tribe, but are distinguished from them in having no antennae, and in being furnished with tentacula.

Many of them, particularly those without shells, are remarkably tenacious of life, sometimes capable of being new formed from a part which may have been separated. By much the greater number of them are defective of head, ears, nose, eyes, and feet.

Some of those in the first order, as the common round worms, have a vascular and nervous system, with the parts of generation, which can be distinctly seen. Some, as the cuttle fish, form a kind of connection between fishes and worms, in possessing gills but wanting fins, &c. while others, as those of the lowest order, or zoophyta, join the properties of the animal and vegetable kingdom together.

The class is divided by Linnaeus, &c. into the following orders, viz.

Intestina—as the earth worm, leech, &c. which are the most simple animals, being perfectly naked, and without limbs of any kind.

Mollusca—as the naked snail, sea-star, cuttle fish; which are likewise simple animals without any shell, but they are brachiated or furnished with a kind of limbs.

Tetraeae—as the snail, oyster, &c. which have the same characters as the former order, but are covered with a shell, and include the greater part of what we commonly call shell-fish.

Lithophyta—as corals, madreporis, &c. which are compound animals fixed upon a calcareous base, constructed by the creatures themselves.

Zoophyta—as the sponge, polypus, &c. These are likewise compound animals, furnished with a kind of flowers, and having a vegetating root and stem.

Some of these creatures inhabit the earth, others live on the rest of the animal or on the vegetable kingdom, and many are found in the hardest stones; while an innumerable tribe of them live in the waters. In general, they are said to be of the hermaphrodite and oviparous kind; while the lowest class, as the polypi, in a great measure resemble the vegetable kingdom in their manner of growth.

Comparative Degree, among grammarians, that between the positive and superlative degrees, expressing any particular quality above or beneath the level of another.