To the concave surface of the right lobe is attached a hollow receptacle in form resembling a pear, and furnished with an excretory duct. This is the gall bladder.
The substance of the liver is of a soft consistence, and of a dusky red colour. When minutely examined, it seems to be almost entirely composed ol the ramifi cations of vessels, though Alalpighi thought he had dis covered in this, as in the other secreting glands, bundles of circumscribed knotted appearances of a globular form, which became more conspicuous when distended by injection, whence he conceived them to be hollow cells or follicles. Dr Saunders seems to favour this opinion of Malpighi, for he says, that "if a subtile injection be thrown in by the vena portarum, and the liver be after wards cut into thin slices, there will be found knotted appearances that bear a strong resemblance to cells, and which, from their equality of bulk and uniformity of shape, cannot be considered as the produce of ext•a vasation." See Saunders on the Liver, 2d edit. p. 65. 'Most anatomists, however, agree with Ruvsch, in sup posing that these globular appearances arise from nu merous minute ramifications of vessels, forming radiated villa or pencils, from which still more minute ramifica tions proceed, till they escape our limited means of investigation.
There is probably no secreting organ that is provided with so great a variety of vessels as the liver. Besides the hepatic artery coming from the coeliac, and the veins which correspond to this artery, there is a very large blood-vessel called the vena portarum, formed by the union of the branches of all the veins that bring back the blood from the stomach, intestines, pancreas, and spleen. The large vascular trunk thus formed, resem bles an artery in its office, and, as some have supposed, in its structure ; for it distributes the venous blood which it has collected from the bowels, through the glandular substance of the liver ; and though it does not possess the principal discriminating mark of an artery, namely the power of preserving a circular orifice when transversely divided, it has thicker coats than other veins, and even sonic appearance of muscular fibres. The vena po•tarum enters the transverse fissure by two large branches, is hick as well as the trunk are inveloped in a membranous coat derived from the peritoneum.
This coat surrounds the trunks of all the vessels that enter the liver, forming a common envelope, which has been called the capsule of Gli.s..•on. It does not, how ever, as that anatomist supposed, follow the ramifica dons of the vena po•taranz any more than those of the other vessels of the liver. Numerous veins come from the and meet in two large branches called vena caves pathic, which convey the. Mood to the great. vt nu cava. Part. ol these veins arise from the reflected ext•e mities of the hepatic artery, and part of them are from the ill'11(1 portaram, so that this last vessel may truly be said to propel its blood, both from its trunk into branch es, and from branches into trunks.
Coming out Irmo the ports or transverse fissure, there arc observed two membranous tubes, which speedily unite in a single trunk, called the hepatic duct, which. conveys the bile secreted by the liver into another mem branous tube, by which it is carried into the duodenum. W hen the two branches that Dorm the hepatic duct are traced through the substance ol the liver, they are found to be composed by the union or innumerable smaller ducts, the origins of which are extremely minute, and are called pori bi/iarii, or biliary pores. The hepatic duct has been supposed to possess muscular contracti bility, but its muscular fibres have never been detected ; and when subjected to the action of ordinary stimuli in the living body, it is not found to contract. It has also very little elasticity, but if we may judge from the pain that accompanies its obstruction by gall stones, it is ex tremely sensible.
The liver is abundantly supplied with absorbents, Loth deep seated and superficial. The former are re markable for being most numerous near the branches of the hepatic duct, and for their very frequent inoscu lations with each other. They appear to be equally valvular with other absorbents, but their valves do not so perfectly obstruct the retrograde passage of fluids. This organ appears to have but few nerves. It re ceives nervous filaments, both from the par vague: and great sympathetics, and especially from that ganglion close to the diaphragm, called the semilunar ganglion.