DIGESTIVE TRACT. 4I 



of the cystic duct is called the hepatic duct ; from that point 

 to the intestines, the ductus choledochus. Again, besides 

 these ducts there may also be a separate hepatoenteric duct 

 leading directly from the liver to the intestine, as well as other 

 modifications not necessary to mention, aside from the numer- 

 ous ducts in lizards and snakes. 



The liver thus formed is a large compact organ, largest in 

 the lower vertebrates, and larger in flesh (fat) eating forms 

 than in the herbivorous groups. In many fishes it forms a 

 single, undivided mass, but in the great majority of vertebrates 

 two lobes are present, and these in turn may be lobulated. The 

 blood-vessels leading to the liver (portal vein, hepatic artery) 

 enter in close relations to the gall ducts, while the veins 

 (hepatic) leaving it are widely separate from these, in contrast 

 to the conditions occurring in most organs. The liver is sup- 

 ported by a mesentery (gastro-hepatic omentum) which connects 

 it to the ventral wall of the alimentary tract, and which is fre- 

 quently continued below as the suspensory ligament of the liver. 



The pancreas develops in much the same way as the liver, — ■ 

 as an outgrowth from the entodermal walls just behind the liver 

 outgrowth. There is the same increase in size, while branching 

 gives rise to glandular portions and ducts. The pancreas has 

 recently been found to occur in several vertebrates where its 

 existence was formerly denied, and farther research may reveal 

 one in the cyclostomes where none has yet been found. Thus 

 in certain teleosts its condition as a dehcate tube lying in the 

 mesentery, and its position in the dipnoi just outside the muscu- 

 lar walls of the alimentary canal, caused it to be overlooked for 

 a long time. In the elasmobranchs and other teleosts it is a 

 well-marked gland. In other forms it is more complex in its 

 origin. Thus in the ganoids (sturgeon) it arises by two dorsal 

 and two ventral outgrowths ; in the amphibia and all higher 

 forms, from one dorsal and two ventral outpushings, these later 

 uniting into one glandular mass. The ducts can undergo vari- 

 ous modifications, all persisting, or either dorsal or ventral dis- 

 appearing ; or finally the ducts may come into connection with 

 those leading from the liver (Fig. 44 C, W"). 



