LIVER AND PANCREAS. The largest of these out-pocketings is the liver. It is phylogenetic ally an old organ, as it occurs in all the verte brates, even in Amphioxus. The form of the liver is always closely adapted to that of the cavity in which it lies. In myxinoids it consists of two lobes, and this is probably the "ground form" of flue organ in all vertebrates. In, many cases it is further subdivided into (dog, weasel) six or seven lobes even. The right lobe is the larger, and in it the gall-bladder, when present, lies imbedded. The liver arises as an evagination of the epithelial lining of the ventral wall of the anterior portion of the intestine. In Amphi oxus it is located ju4 behind the gill region. The hepatic fundaments are soon transformed into glands made up of branching tubules. The net work of tubules early differentiates into excre tory and secretory parts. In amphibians and reptiles the tubular nature of the gland is easily recognizable, but in higher vertebrates (birds, mammals, man) the tolmlar structure is incon spicuous. Simultaneously with the development of the tubules a meshwork of blood vessels ap pears in the liver. In birds a ml mammals at the point at which the primary bile ducts open into the duodenum a small evagination is formed. This evagination elongates to form the bile duct. The gall-bladder is a reservoir for storing the gall. It develops as an evagination of the bile duct or from the hepatic duets. The liver serves as a storehouse in which the sugar not needed by the system for immediate consumption is stored up in the form of glycogen; it destroys the old red blood corpuscles and oxidizes nitrogenous materials into urea. Its function in digestion is less clearly understood. Fats, however, more easily pass through a membrane moistened with bile, and a greater proportion of fat passes unab sorbed through the intestine of a dog when the bile duct is stopped; hence bile probably aids in some way in the absorption of fats. The alka
linity of the bile also aids the pancreatic juice in overcoming the acidity of the gastric juice. Bile also aids in stimulating the action of the muscles of the intestine. Its absence leads to biliousness and even jaundice, and finally the bile acts as a preservative when deficient putre faction of the contents of the alimentary canal results. The pancreas also arises as an evagination of the alimentary tract, but from the dorsal side of the duodenum, and usually opposite the origin of the liver, Except in cvclostomes and some teleosts, the pancreas is always present in vertebrates. Its size and form varies, and it is not infrequently lo bate, In structure it is a racemose gland. Its secretion is either poured directly into the intestine (as in birds, crocodiles, Emydidte, and some mammals), or as development proceeds its outlets move nearer and nearer the bile duct, and finally the secretions of the liver and pan creas are poured into the intestine through a common duct. The pancreatic secretion is alka line. Its role in digestion is very great. Its action on starch is like that of the saliva, only much more energetic. Through the agency of the ferment trypsin it effect-3 proteids, and by an other ferment, steapsin, fats are split up into fatty acids and glycerine. The soap and glycer ine are both soluble in water and hence are easily absorbed. Aluch of the fat, however, is emulsi fied by the albumen, that is to say, it is broken up into fine drops, which are prevented from fusing by the presence of a coating of albumen. The fat in the emulsion is probably capable of absorption as it is.