250 COMPARATIVE MORPHOLOGY OF VERTEBRATES 



liver, that of the myxinoids being in two parts. It is larger, too, in 

 the flesh-eating than in the herbivorous species. The blood supply, 

 chiefly through the portal vein and to a less extent by the hepatic 

 artery (see circulation), is very large. The color of the gland is very 

 variable, especially in teleosts, where it may be brown, yellow, 

 purple, green and even vermilion. 



THE PANCREAS 



The second largest of the digestive glands, the pancreas, secretes 

 digestive ferments of great strength (trypsin, steapsin, amylopsin), 

 which digest both proteids and carbohydrates. In some respects it 

 resembles the salivary glands and so compensates in part for the 

 absence of them in the lower vertebrates (p. 235). The pancreas 

 arises by diverticula from the wall of the intestine close to the liver 



ccp 



Fig. 269. — Diagram of developing pancreas of cat, after Thyng. c, ductus coledo- 

 chus; d, duodenum; dp, dorsal pancreas; ccp, its duct; i, small intestine; s, stomach; c^ 

 ventral pancreas. 



(fig. 268). There are usually three of these diverticula, one dorsal 

 and two ventral, the ventral soon uniting (fig. 269), but in the sharks 

 there is only a single dorsal diverticulum, while in the sturgeon there 

 are two dorsal and two ventral. In a general way these develop 

 much like the liver, the distal portions of the divisions forming the 

 glands, which are of the acinous type ; the proximal portions form the 

 ducts. Of these ducts all may persist; all but one may disappear, 

 while in the lampreys all may be lost. In many mammals two ducts 

 persist, the ventral forming the main pancreatic duct (Wirsung's 

 duct), the dorsal, the accessory or Santorini's duct. The ducts may 

 remain distinct; they may unite before entering the intestine or one 

 of them may unite with the bile duct. 



For a long time it was supposed that a pancreas was lacking in 



