The Liver is, by far, the largest gland in the human body, and is so disproportionate to the quantity of liquid secreted, that the bile must require a very extensive apparatus for its elaboration; and this inference is strengthened by an examination of its composition, for few fluids are so complex, and so different from the blood. A knowledge of the locality of the liver is a fact of considerable importance to the practitioner, as he is frequently called upon to investigate diseases which depend, or are supposed to depend, upon organic changes in the structure of this viscus. Under such circumstances, the patient must submit to a manual examination; and the medical student who is unacquainted with the situation of the liver, with respect to the general cavity of the abdomen, or with the changes which its position may undergo from various circumstances, will frequently find himself involved in difficulty and confusion.

34. The liver is situated in the superior part of the abdomen, principally on the right side: it generally occupies the epigastric and the right hypochondric regions; but, since the inferior part of the chest may be diminished in capacity, or altered in figure, these regions may, by suffering a corresponding alteration, become too much contracted to contain it; in which case it will extend into the left hypochondric region, and may even occupy no inconsiderable part of the umbilical region. This occurs in females, whose chests are naturally contracted, or have become so by the barbarous custom of tight lacing, and from which more mischief has arisen, than from all the dietetic errors which I shall have occasion to enumerate.

35. As the liver is connected with the diaphragm by doublings of the peritonaeum, termed ligaments, it follows that, in the living subject, it will vary with respect to the general cavity, in the acts of inspiration and expiration.

36. The figure of the liver is also found to vary in different animals, being generally determined by that of the animal itself, or by that of the cavity in which it is contained. In the human subject it is somewhat convex on its anterior, irregular but concave on its posterior, surface; it is extremely broad superiorly, but gradually becomes thinner inferiorly, and terminates in a thin margin. Its surfaces are smooth, being covered by the peritonaeum, which forms its several ligaments. At the inferior edge of the liver there is a fissure extending some way up, particularly on its posterior surface, which divides it into two lobes of unequal size. These, from their situation in the abdominal cavity, are distinguished by the names of the right and left lobes, of which the right is the larger. Besides these, there is a smaller lobe, situated at the superior and posterior part, called, after its describer, lobulus Spigelii. The liver usually weighs, in a middle-sized man, about three pounds twelve ounces.

37. In a depression on the concave surface of the right lobe, a pyriform-shaped bag, termed the gall-bladder, is lodged; it has a duct inosculating with that from the liver, through which the bile enters its cavity, and, at the same time, it constitutes the only outlet through which that fluid can pass into the intestine.

38. The pyloric portion of the stomach is generally covered by the left lobe of the liver, and the gallbladder would appear to rest usually on the duodenum.

39. The liver is composed of arteries, veins, nerves, lymphatics, and excretory ducts, united by a peculiar parenchymatous structure. In every other gland in the body, the same blood which supplies it with nutrition is also adapted to its secretory office, and is conveyed to the organ by the same vessel: but the liver requires arterial blood for its nourishment, and venous blood for the materials of its secretion; the hepatic artery supplies the former, and the vena portarum conveys the latter. This vein is formed by the concurrence of all the veins of the abdominal viscera, which gather together and constitute one large trunk, called the sinus of the vena portarum, which enters the liver, and divides in the manner of an artery. This peculiar arrangement induced some physiologists to suppose, that the bile was prepared in the abdominal viscera, or rather, that the blood underwent some peculiar modification in the intestines, which prepared it for the peculiar change it was destined to undergo in the liver; and they have supported this opinion by another equally gratuitous, that the blood of the vena portarum is better adapted for the secretion of bile, on account of the larger proportion of carbon and hydrogen which it must contain; but Bichat has observed, that fat, which is a highly hydrogenated fluid, does not require venous blood for its secretion; and contends that the bile is secreted from the arterial blood of the liver, since the quantity of the latter sent to the liver is more in relation with the quantity of bile formed, than that of the venous blood; and that the volume of the hepatic canal is not in proportion with that of the vena portarum.

M. Majendie seems inclined to believe that both kinds of blood may serve in the secretion: he thinks that such a theory is indicated by anatomy; for injections prove that all the vessels of the liver, arterial, venous, lymphatic, and excretory, communicate with each other. This idea, however, is highly repugnant to that simplicity which Nature observes in all her operations; and, although I am not prepared to prove that the blood of the vena portarum has more analogy with the bile than the arterial blood, still, the peculiar structure, disposition, and terminations of this singular vein appear to testify the important function it is destined to discharge. M. Simon has shown, by recent experiments upon pigeons, that when the hepatic artery is tied, the secretion of bile continues: but that if the vena portarum and the hepatic canals be tied, no trace of bile can be subsequently found in the liver: several pigeons survived the latter operation for six-and-thirty hours. It appears evident, therefore, that in these animals the secretion of bile takes place from venous blood.