every other texture. These extreme branches of the | arteries being so minute, anatomists have had great difficulty in tracing the exact point at which they pass into veins. That they do so, however, is undeniable, and is partly seen on the surface of the brain. The veins are another system of vessels, which return the blood from the extremities of the body to the heart. They are larger and more flaccid than the arteries, and are distinguished from them by having no pulsation. A large vein generally accompanies the corresponding artery, but the great proportion of the veins lie more towards the surface, and are easily distinguished, swelling out under the skin. The numerous veins from the lower extremities join into one trunk in the belly, which vein, after passing through the liver, as will be afterwards described, joins the right auricle of the heart, the blood from the upper half of the body joining also by another similar vein. In the veins of the extremities that hang downwards, and are apt to be gorged with blood, there are inserted numerous valves, at short distances, which prevent reflux of any kind. THE BRAIN-NERVES AND NERVOUS INFLUENCE. The brain, as already mentioned, is contained in the cranium. It is a soft mass of matter, enclosed in certain protecting membranes beneath the bones of the skull. As the organ by which mind acts, and chief seat of the nervous energy, the brain may be described as the most important and dignified of man's bodily parts, and well deserves the most careful investigation. The brain is divided by strong membranes into two main sections-the cerebrum or proper brain, which lies in front beneath the brow and on the top and sides of the head, and the cerebellum or lesser brain, which lies behind. Both are longitudinally divided into halves or hemispheres, and also into lesser parts called lobes. The annexed figure offers a lateral representation of the different parts of the brain, as it lies beneath the skull, with its beautiful and minute radiation of nerves proceeding to the eye and other external instruments of the organs of sense. The cerebrum or principal part of the brain is indicated by the letters, a a a. The cerebellum, distinguished by the letter b, terminates below in the medulla oblongata, c, the cylindrical pulpy cord by which a union is formed between the brain and spinal marrow, d. The latter part is the long cord of soft matter formerly mentioned as lying in the canal formed by the range of the spinal bones. It is round, of the thickness of the finger, of the same kind of substance as the brain, and formed of smaller nervous cords, running parallel to each other: it runs along the whole length of the back down to the pelvis. The nerves are small whitish-looking cords, which proceed from the brain and spinal marrow, and spread out in innumerable branches to every part of the body. A large branch of a nerve generally accompanies every large artery, and every important part of the body has a branch of a nerve sent off to it. The nerves for supplying the organs of smell (1), of seeing (2), of hearing (3), together with the great sympathetic nerves, which give branches to the heart, lungs, stomach, and other important viscera, proceed directly from the brain. The nerves of motion and sensation sent to the various parts of the trunk and extremities, take their origin, with a few exceptions, from the spinal cord. Two sets of nervous branches proceed from the cord on each side, corresponding nearly to the junction of every vertebral bone; and it is found that a branch of these nerves imparts motion, and the other sensation or feeling. The brain has a covering of three thin membranes; the outward one strong and thick, the inner extremely thin and delicate. The nerves, which are soft and pulpy inside, have also a thin external covering which protects them. The nervous branches are never seen or felt in the living body, and what are vulgarly called nerves, are the tendons of the muscles, the erroneous title being given chiefly to those about the wrists, fingers, and ankle-joints. Their great numbers and minute divisions are manifest, however, because we cannot prick any part of the body with the sharp point of a needle, without wounding some of them, and thereby causing the sensation of pain. When the nerves are injured in their powers by disease, the sense of feeling in the part is entirely lost. The brain in the lower animals is not generally nearly so large, in proportion to their bulk, as in man; and the cerebrum, or upper brain, is often smaller in them than the cerebellum, or lower brain. In many classes of the inferior animals there is no distinct brain, but only nerves running along their bodies, and joining into knots or ganglions. The nervous system of insects and worms is of this description. In the polypus, and some other similar animals, a distinct nervous system can scarcely be traced. It may be proper here to make some observations on the functions of the brain, considered abstractly from its anatomy. Man surpasses all other animals in the height and proportions of the forehead, and in the comparative mass of brain in the upper part of the skull. In the human head the lower parts of the face bear a smaller proportion to the forehead than in the brutes. The face is placed in nearly a perpendicular line with the forehead, instead of projecting outwards into a snout, as in the lower animals. The brute face is merely suited for the purpose of animal wants and for defence; the jaws are long and narrow, supplied with thick, strong muscles, and short teeth; there is not the elevated nose, which in man forms a distinguishing feature-the arched eyebrows-the exquisitely formed lips, and the rounded chin; above all, there is not that play of varied expression, that air of intelligence, and that indescribable emanation of a rational mind, that ray of divinity, at the appearance of which the most wild and ferocious of the brute creation are awed and subdued. But, besides, the Creator seems to have allotted characteristic external signs to express the passions of the mind, that in social life man might not easily impose on his fellow-man; for the various muscles of the face express the several passions of the mind so faithfully, that they may be even represented in painting. This is said to be the natural expression, and would appear to be understood even by animals; for a dog, on looking to the countenance of his master, easily recognises the mute expressions either of commendation or dissatisfaction. From the action of these muscles being so often repeated, physiognomy arises; the action of the prevailing | The lungs have a dark bluish appearance, a familiar exmuscles fixes an enduring expression on the features; ample of which is afforded in the lights of sheep, that and thus traces of frequent anger often remain in the part generally appended to the heart and wind-pipe. countenance after the passion itself is gone off. With Inside they are composed of an immense number of the power of speech and reason, man has also the cells, which alternately inflate or collapse as the lungs means of expressing his feelings and passions by laugh- are filled and emptied of air. When an inspiration is ter and weeping, manifestations which are not found in made, and the lungs are filled with air, these cells bethe lower animals. Weeping proceeds from a deep come expanded; and the blood sent from the right side emotion of the mind, and seems an effort of nature to of the heart, and spread over the cells, is exposed through relieve the system of grief. It usually begins with deep an extremely thin membrane to the air. An important inspirations of the lungs, after which follow short alter-change, as formerly alluded to, here takes place on the nate inspirations and expirations, and it is finished with blood: from being of a dark purple colour, it immea deep long-drawn expiration, which is immediately fol-diately changes to a bright scarlet, having absorbed or lowed by an inspiration. When moderate, it certainly taken up all the oxygen, or vital part of the air, and relieves the distress arising from grief. Laughter has parted with a corresponding volume of carbonic acid its rise from some ludicrous ideas impressed upon the gas or fixed air, which it had acquired in its circuit mind, and would seem to arise directly from a sort of through the vessels of the body. So essential is the titillation conveyed to the branches of certain internal matter imparted by the air to the blood for sustaining nerves, probably those of the diaphragm ; immediately animal existence, that the breathing cannot be susto this succeeds a number of imperfect inspirations and pended even for a very short period without extinguishexpirations, which seem to be checked by the contrac-ing life. It is probable, too, that the heat of the body tion of the glottis in the throat or larynx. Laughter is generated, and constantly kept up, in some way or in a moderate degree may be conducive to health, as it other, by means of this process of breathing, and the gives impulse to, and ultimately promotes, the circula- change which the blood undergoes. We know, at least, tion; carried to excess, however, it may prove danger- that the evolution of carbonic acid cannot go on, in ordious, from accumulating too much blood in the lungs. nary chemical processes, without an accompanying disSneezing consists of one deep inspiration, succeeded by charge of heat; and hence it is presumed that the vital a powerful single expiration, and seems to consist of a warmth, derived by the body from the blood, may be convulsive effort of the muscles of breathing to throw in this way produced. The lungs, like every other off some cause of irritation in the sensitive membrane internal organ, are covered with a thin transparent of the nostrils. The common hiccup is a spasmodic membrane called the pleura: this membrane, as well action of the muscles of the stomach, caused by some- as the substance of the lungs themselves, is liable to thing irritating the stomach itself. Some of the causes inflammation; and hence the name of the disease called by which our mental happiness is either increased or pleurisy. The trachea or windpipe, the communicadiminished, proceed entirely from the bodily sensations. tion between the mouth and lungs, is a hollow tube, Any gentle stimulus applied to a nerve seems to cause having a series of cartilaginous rings passing round a feeling of pleasure; strong stimuli, or any causes dis- it, to prevent the possibility of its being compressed turbing seriously the natural condition, produce pain. either by external means, or from the food in the act Itching is akin to pleasure, and in both cases the flow of of swallowing, and, in consequence, the breathing obblood is increased into the part in which either plea- structed. It takes its rise from the bottom of the sure or titillation is perceived; but when farther in- mouth, and passes down in front of the neck, where its creased, it degenerates into pain, or excessive sensations strong cartilage may be seen and felt. At its lower in the nerves. Anger violently excites the motion of part it divides into two parts, like the prongs of a fork, the spirits, increases the motion of the heart, the fre- one going to join the right section of the lungs, the other quency of the pulse, and the strength of the muscles; the left. Lungs for breathing air are only found in the forces the blood into the extreme vessels; and even some- higher classes of animals. Fishes are furnished with times bursts the smaller vessels themselves: passion gills, those comb-like substances which lie within a flap also increases the secretion of bile. Grief weakens the on each side of the head; over them a stream of water strength of the nerves and action of the heart, retards is constantly sent by inhaling it at the mouth in a the pulse, destroys the appetite, and frequently produces similar manner to breathing. The air, which is always paleness, looseness of the bowels, indigestion, and those present in considerable quantities in water, is thus slow or lingering diseases that take their rise from an absorbed by the blood-vessels while ramifying over the interruption of the secreting glands, and a disease of gills, and all the purposes of breathing are answered. their structure. Fear diminishes the force of the heart, In insects there are no lungs, nor do they breathe by weakens the muscular motions, relaxes the whole system, the mouth, but along the sides of their bodies, by means and, if long continued, causes a general sinking of the of numerous holes with small tubes or spiracles, leadbody. Excessive terror often increases for the moment ing to a longer middle tube, by which the air enters the muscular strength, even to convulsions; excites the and mixes with their fluids. When we descend lower pulse, interrupts the course of the blood, and in not a in the animal scale, even this substitute for breathing few instances has produced sudden death. Love, hope, ceases, and probably the vital air is absorbed by such and joy, promote all the salutary actions of the body, animals by simple pores or openings in the skin. gently quicken the pulse, promote circulation, increase the appetite, and aid the cure of diseases. Excessive and sudden transports of joy, however, often prove fatal, by increasing the motion of the blood, and exciting a fit of apoplexy. Shame, in a peculiar manner, retains the blood in the face, as if the veins were obstructed; when felt in an extreme degree, it has also been known to prove the cause of sudden death. THE LUNGS OR BREATHING APPARATUS. In the highest part of the cavity of the chest, on each side of the breast-bone, the lungs are situated. A membrane passing from the breast-bone to the back, divides them into two portions, the right lung and the left lung. The right lung consists of three sections called lobes, the upper, middle, and lower; the left lung, rendered smaller in bulk by the presence of the heart in the same cavity, has only an upper and a lower lobe. THE TEETH.-DIGESTING APPARATUS. The first process performed in connexion with the supply of nourishment to the body is that of masticating the food, and this is the office of the teeth. The Teeth.-These are placed in the upper and lower jaw, to which they are attached by roots, which sink into the porous sockets of the jaw, somewhat in the same manner as a nail is fixed in a piece of wood, though they are retained in place chiefly by the softer parts around. The teeth are composed of bony matter, covered externally with a thin coat of an extremely hard substance, called enamel. The teeth are furnished with nerves and blood-vessels, and have thus vitality like the rest of the body, although possessing it in a less perfect degree than most other parts of the structure. Hence they are very liable to disease and decay. In decaying teeth a blackish spot is first perceived upon the outer crust or enamel; this substance gradually gives way, and then the bone below proceeds to rapid decay. The irritation of the air, and particles of the food, inflame the nerves and soft pulpy parts inside, and thus the excruciating pain of toothache is produced. The first set, or temporary teeth, begin to make their appearance in the child about the fifth or sixth month, and towards the end of the eighteenth month the whole set of temporary teeth, consisting of twenty, have generally cut through the gums. These teeth continue till about the sixth or seventh year, from which time, till about the twelfth or thirteenth year, they gradually fall out one by one, and are succeeded by the second or permanent teeth. The roots of the temporary teeth are much smaller, and sink less deep into the jaw than their successors. The rudiments of the second set of teeth begin to form early in cavities below the others, and, gradually growing and pressing upwards, displace them. The number of the permanent teeth is thirtytwo, consisting of sixteen in each jaw. The four front teeth are called the incisors, and have one long root; on each side next to these is one eye or dog tooth; then there are placed two small grinders on each side, having double roots, and three large grinders, or molar teeth. The last of these is called the wisdom tooth, from its making its appearance latest in the jaw, from the seventeenth to the twentieth year, or even later. By this change and gradual succession of teeth, we have a beautiful provision of nature for permitting the jaws to increase in size, and, at the same time, for preserving the relative positions and regularity of the different teeth; for had the first teeth of childhood been permanent, it is impossible that the jaw could have increased in growth without deranging the order and position of the whole. The teeth of various animals differ according to the kind of food on which they live. In carnivorous, or flesh-feeding animals, the teeth are sharp-pointed, and adapted for tearing their prey to pieces; in those animals called graminivorous, that live on grasses and other herbage, the teeth are of a rounded forin, with broad surfaces, and the grinders are furnished with several layers of the hard enamel, following each other in succession, with a slight layer of common bone interposed; so that, when the grinder is worn down by the friction of chewing, it is not rendered useless, but a new layer of the enamel is presented at the worn-down surface. Some animals, as the hare, rabbit, beaver, and mouse, have the front teeth of a chisel shape, with enamel only on the outer side of them. These animals are called gnawers, because they chew or gnaw down their food in this particular manner; and by the inner soft part of the tooth being liable to be worn down, while the outer is harder, the enamel is thus always kept with a sharp edge. Some animals have large projecting tusks for defence, as the elephant, wild-boar, &c.; others, as fishes, are provided with teeth more for holding fast their prey than for mastication. Many have no proper teeth at all, as birds, worms, and other soft formed animals. Man is characterised by having all his teeth set close to each other in a half circle; they are of a medium form, between that of carnivorous and herbivorous animals; the front teeth are adapted for cutting; the canine are sharp, though not of undue length; and the grinders are suited for masticating vegetable and farinaceous matters, as nuts, &c. In short, the form of the teeth of man evidently points out that he is adapted to live on a mixed kind of diet, or a conjunction of vegetables and flesh. Stomach.-Behind the windpipe, taking its rise also from the bottom of the mouth, lies the oesophagus, or tube which passes into the stomach. This tube expands at the top into what is called the pharynx, forming the whole of the upper part of the throat immediately behind the tongue. Into this cavity the windpipe opens, and, to guard against any particle of the food or drink passing into the windpipe instead of into the passage to the stomach, there is a little tongue or valve which closes accurately over the mouth of the windpipe every time food or drink is swallowed. When the substances have passed, the valve again springs open, and admits of free breathing. To show how accurately and precisely every part of the human machine performs its duties, a celebrated writer has instanced this same valve, which, in a multitude of persons dining together, not one time out of a hundred in any one individual instance is at fault. When a drop of fluid or particle of food does by chance insinuate itself into the windpipe, so sensitive is this tube, that a convulsive cough is excited till it is again expelled. There is another little tongue or flap attached to the roof of the palate, and seen above the tongue when the mouth is opened. This, which guards the passage to the nose, is not, however, to be confounded with the other, which is farther down the throat, and invisible. The oesophagus, or gullet, passes down through the chest, traverses a ring in the diaphragm, that large muscle which stretches across the lower ribs, and which assists so materially in breathing. Immediately below this muscle, on the left side, is situated the stomach, which is partly sustained in its place by being attached to the oesophagus, or tube from the mouth. The stomach is an oval bag of considerable size, occupying a slanting position immediately below the heart, with its right side overlapped by the left edge of the liver, and extending to the lower end of the breast-bone. The stomach has three coats-an external membranous one, a muscular, and a soft villous inner covering. The upper passage, by which this bag communicates with the oesophagus, is called the cardiac opening; the lower, where the first gut commences, is called the pyloric orifice. Digestion.-One of the most important operations in the animal economy, is that of digestion, whereby the various substances used for food are dissolved in the stomach, and undergo changes, by which they are formed into matter fit for entering into the composition of the different parts of the body, to nourish its growth, and supply the daily waste which takes place in the system; for such is the constitution of animal bodies, that the substances of which they are composed are liable to constant waste; the solid parts are worn down, and a large quantity of fluid is constantly given off by the exhalent vessels, both from the skin and the surface of the lungs. This is manifest in the sweat and the vapoury exhalations constantly passing off by the mouth; and there is also an imperceptible perspiration regularly proceeding from the surface of the body, which has been computed to amount to several pounds in the course of a day. It must be evident, therefore, that if this waste was allowed to proceed but for a very short period, the body would soon be reduced to a state of complete decay. A constant supply of new material is therefore daily needed, to replace that which is wasted; and thus it has been supposed that a human body changes its whole materials many hundred times from the period of its birth till death; and that an individual, as regards his mere corporeal structure, is not at all the same at the period of manhood to what he was when a boy, nor in old age what he was in his prime. Although this change then is complete, even to the bones and most solid parts of the frame, it is brought about so gradually, and with the regular and minute substitution ofone particle for another, that it is never perceptible. Man has been called, with relation to his diet, omnivorous, from his being adapted to live on every kind of food, whereas most other animals are confined to one particular description. The carnivorous animals live on flesh alone, the graminivorous on grass and green herbs, and the granivorous on grains and other smaller seeds. These animals never change their respective diets; nor, from the construction of their teeth, stomachs, and intestines, were they ever intended to do so. But in man it is plainly evident, from his anatomical structure, that he was intended to feed on every sort of food promiscuously, or that he could adapt himself to either animal or vegetable fare, as habit or necessity impelled him. Man also differs from brutes in resorting to the arts of cooking, whereby the food is put into a state more fitted for digestion, and for yielding a sufficiency of nutritious aliment. The short time to a thin pulp, it will not usually act on the living fibre; so that, after death, the coats of the stomach have been found dissolved into holes, by the same juice, which, in the living body, had no such effect. This forms a most important fact in medical jurisprudence. A stomach of some kind or other is found in all animals; for it is by this organ that nutrition and growth are solely promoted. There are some very simply formed animals whose whole body consists of an oval hollow bag, or stomach, with a simple outlet for the mouth to take in nourishment, and no other organ whatever. The common polypi have simply a arms, by which the creature seizes the worms and grubs on which it feeds; these it swallows, abstracts their juices, and then voids the remainder from its mouth. The common leech has its whole body divided into a number of small cells, like a piece of honey-comb; and these receive the water, and sometimes blood, on which it feeds. Flesh-feeding animals have a simple bag for a stomach, and their food is easily and soon digested. Those animals, again, that feed on grass, which is of more difficult digestion, have three and four stomachs, into which the food successively passes after it has been masticated or chewed a second time in the mouth. This is the case with cows, sheep, deer, &c. Birds that feed on grain have first a sap-bag, or crop, into which the food enters, and remains for a considerable time, mixed with a juice somewhat like saliva; here it is softened and rendered moist, preparatory to its passing into the true stomach, or gizzard, which is an extremely strong muscular bag; in this, with the assistance of a number of sharp-pointed pebbles, which such birds always swallow, it is ground down and acted on by the gastric juice. This compensates for the deficiency of teeth in fowls. Crabs and lobsters have no teeth in their mouths; but in their stomachs will be found three or more teeth, which assist in grinding down the tough sea-weed on which they feed. By domestication, the qualities of the gastric fluid may be so changed, that animals accustomed to live entirely on flesh will exist and thrive on a vegetable diet. This is the case with dogs, and many birds. All these peculiarities in the natural history of animals illustrate, at least directly, the uses of the digestive organs in the human being. food being received into the mouth, is broken down and masticated by the teeth. It is here also reduced into a soft pulp by the saliva, which flows into the mouth by the salivary glands; and thus being sufficiently broken down and softened, it passes into the stomach. The stomach has numerous glands situated on its inner coat or surface, which secrete a peculiar fluid called the gastric juice, which is clear and colourless, with little taste, or smell, or sensible qualities. On this fluid depends the important office of digestion. It has the power of coagulating substances in the stomach, of preventing the contents of the stomach from passing into a state of fermentation or putrefaction, and of dissolv-mouth and hollow stomach, with several tentacula, or ing the whole into one homogeneous mass. When the stomach is first filled with food, it appears to remain there for a short period without undergoing any change; gradually, however, successive portions of the food, as they come into contact with the gastric fluid, are dissolved; till at length, in a shorter or longer period, the whole is collected into a thin greyish paste, called chyme. In the upper or left division of the stomach, it would appear, from some recent observations, that the food is freed from its superabundant moisture, which drains off by some undiscovered means to the blood-vessels, and from thence to the kidneys. The chyme then, as it is gradually formed, moves to the other extremity of the stomach, called the pyloric, where it passes out to enter the intestinal canal. It would appear, also, that the pylorus, or lower mouth of the stomach, has a sensitive power, whereby it freely permits the digested chyme to pass out, but refuses exit to the undigested matter. The chyme having passed into the first part of the intestines, or duodenum, is then mixed with the bile from the gall-bladder, and with the pancreatic juice. Both these substances, especially the bile, seem essential for the conversion of the chyme into proper alimentary matter, but their peculiar action has not yet been satisfactorily explained. That the liver and bile ducts are of the utmost importance, however, cannot be doubted, from their magnitude, and the care with which they are supplied with numerous vessels, and from their being universally present in a great proportion of animals. The chyme having passed through the duodenum, and having been mixed with the bile and pancreatic juice, now changes its appearance and properties, and becomes the chyle, or nutritious matter destined to supply the various parts of the system with nourishment. The digested mass is passed gradually along the course of The Liver-Opposite the stomach, on the right side, the small intestines, urged forward by what is called lies the liver, a large flat substance, of a dark brown their peristaltic motion, which is effected by a succes-colour, divided into two lobes. The liver has a round, sive contraction of their fibrous coats. Here the minute convex upper surface, and is hollow or concave below; mouths of the lacteal vessels, opening on the inner sur- it is also thick and solid at the back part, and its edge face of the small intestines, take up the chyle, and carry becomes thinner towards the front, where it lies over it, as has already been described, to the receptacle of a portion of the stomach and bowels. It is suspended the chyle, and then by a duct running up the chest along in its place by several ligaments attached to the surthe spine, called the thoracic duct, it joins the blood- rounding parts. In the under side of the liver, in a vessels. The refuse of the aliment which has not been small hollow, is situated the gall-bladder, a small oval taken up by these lacteal vessels passes on through bag which contains the bile. A tube from this bladder, the large intestines, and at length is ejected from called the bile-duct, passes into the upper portion of the body. Digestion is not brought about, as has by the bowels, carrying the bile there. The liver is supsome been supposed, by any mechanical means, as by plied by several branches of an artery in the usual way the grinding powers of the coats or sides of the sto- that the other organs are, but it has also a peculiarity mach, nor by heat alone, nor fermentation, nor by which no other organ of the trunk possesses. The the simple resolution of the food into a fluid; but it large veins, which return the blood from the lower is evident that it undergoes a series of chemical ac- part of the bowels, before going to the heart, enter tions in the stomach and bowels, whereby its nature the substance of the liver, and there spread into inand properties are completely changed; and thus ani- numerable branches throughout its whole surface. mal and vegetable substances, however different, are re- From this venous blood the bile is supposed to be duced to one peculiar kind of fluid, the chyle, which, secreted, and after having yielded this substance, the though it may be found to vary slightly according to vessels collect again into one large trunk, and join the kind of food, is, in its general properties, always the large vein which carries the blood to the heart. the same. The gastric juice varies in different animals. The liver weighs, on an average, from three to four In those which feed on vegetable matter, it dissolves pounds weight, and the quantity of bile which it se these substances only; whereas grain and vegetables cretes, taking into account its large supply of blood, pass through the stomach of a purely carnivorous ani- must be very considerable. The greater proportion mal without undergoing any change. The gastric juice of animal beings are provided with an apparatus of has this singular property, too, that although it readily some kind or other for preparing a supply of bile, dissolves dead animal matters, and reduces them in a and in many the liver bears a large proportion to the THE LIVER, &c. other contents of the belly. In some animals, as the horse, the gall-bladder is awanting, there being merely a duct to convey the bile into the intestines. In the lowest classes of animals, all traces of liver or gallducts disappear. THE BOWELS. series of extremely small tubes, and, joining and interweaving, form numerous glands, especially in the groin, armpits, and neck; when swelled by disease, they harden and enlarge, forming knots like a pea or bean. But they are no less numerous on the surface of the inner The Spleen. This substance is situated below the cavities of the body as on the skin; they are found in stomach, on the left side, betwixt it and the ribs. It the brain, on the surface of the lungs, where they give is in shape a flat oval, and of a dark iron colour. No out a large proportion of vapour at every expiration of duct or opening has been discovered proceeding from the breath, and in the abdomen or belly. It is a disease it, nor has its use been as yet accurately ascertained. or sluggishness of these vessels, whereby they do not It possibly serves to relieve the stomach of its surplus perform their necessary duty of taking up all the superquantity of blood while this organ is distended with abundant fluids, that causes accumulations of water food; and the splenic vessels have also been held by in the chest, belly, and legs. The branches of the lymsome to contribute to the secretion of the gastric juice. phatics of the lower half of the body join the receptacle The spleen, it is remarkable, has been frequently cut of the chyle; those of the upper part enter the thoracic out from living dogs, without causing any apparent duct just before the latter pours its contents into the derangement in the health or digestion of these animals. subclavian vein. The Pancreas.-This substance, known under the name of the sweet-bread, is a large oblong gland (or secreting organ), lying across the back part of the belly, extending between the spleen and the middle of the liver. This gland pours out a substance something like the saliva or spittle of the mouth; and by means of a small duct or canal, empties it into the upper bowels, along with the bile from the gall-bladder, both these substances aiding in digestion, and the preparation of the nutritious fluid to be afterwards mentioned. Lacteal Vessels.-These are innumerably small tubes, proceeding from the ileum or small intestines, along their whole course, and spreading along the mesentery, where they form an immense number of small knots, or glands, by joining together. These are the vessels which take up the fluid chyle, or milky-like substance, after it has been digested and properly prepared in the stomach and bowels. From these mesenteric glands, the chyle is conveyed by these ducts or canals to another large gland, situated in the loins, on the right side of the aorta, and immediately below the diaphragm, called the receptacle of the chyle. From this receptacle the thoracic duct arises, and passing upwards by the side of the aorta, or great artery of the body, it joins the left subclavian vein, lying under the left clavicle or collar-bone, and thus pours the whole of the chyle into the general circulation. The Kidneys. These are situated in the loins, one on each side of the back-bone, about one-third up the spine. They are in shape somewhat like a French bean, and their internal structure consists of a number of minute porous tubes. They each at the middle hollow part receive a large artery, and their use is to filter from the blood the superabundant fluid, and salts and juices unnecessary for the system, and transmit these, by means of two small tubes, called the ureters, to the urinary bladder. These tubes enter the back part of the bladder in a slanting direction, which serves the purpose of valves, preventing a flowing back of the fluid when the bladder is full. The bladder is situated in front, immediately above the bone of the pelvis, called the pubis. The whole cavity of the belly is lined by a thin membrane, called the peritoneum, which is double, being reflected from the sides of the cavity over the whole of the intestinal organs. This peritoneum is liable to inflammation, in the same manner as was mentioned of the pleura, which produces a very violent disease. The coats of the intestines, too, are also subject to the same affection. Dropsy may arise from water being formed between the two folds of the peritoneum. The Lymphatic Vessels.-These are another distinct set of vessels spread over all the inner cavities of the body, and also throughout the skin, on which they open by innumerable small mouths. Their office appears to be to take up from the blood a thin lymph, which they convey into the receptacle of the chyle and thoracic duct, and also to exhale or carry off from the skin the superfluous moisture of the body. This moisture forms the sweat, and several pounds of fluid are daily drained off from the body in this manner, even when little or no bodily exercise is taken, for perspiration continually goes on insensibly. These vessels are composed of a From the lower or pyloric orifice of the stomach, the duodenum, the first portion of the intestinal canal, takes its origin. This gut passes below the liver and receives the bile-duct, and the duct from the pancreas, when it terminates in the jejunum, which again passes into the ileum, or principal portion of the small intestines. These are of great length, and occupy a great part of the abdomen, being folded and twisted backwards and forwards in many intricate windings. At the end of the ileum, the colon, a large gut, makes an arch upward towards the right side, and across the belly, and descending at the back part, ends in the short bag, called the cæcum, which joins the rectum, the termination of the intestinal canal. The whole length of the intestines in man is generally about six times that of his average height, or from thirty to thirty-six feet. In all animals that feed on vegetables, the intestines are of great length; whereas, in those that derive their nourishment from animal food, they are of much shorter proportions. Two membranous substances, called the omentum and mesentery, run along nearly the whole length of the intestines, and serve as a means of their attachment and proper suspension in their places. The bowels have three coats-an external one, common to them with the other viscera, a muscular coat, and an internal mucous covering. |