PANCREAS 



349 



dermic outgrowths. These are respectively dorsal and ventral in 

 position, and in most Craniates one dorsal and two ventral 

 rudiments can be recognised, of which one or more may undergo 

 reduction or fusion later, so that the number of ducts opening into 

 the intestine varies in the different groups: there may be only 

 one, or there may be several (e.g. Birds, Crocodiles, Emydse, and 



FIG. 257. PANCREAS AND LIVER OF FROG, TO SHOW THE ARRANGEMENT OP 



THEIR DUCTS. 



Dcy, cystic ducts, which, together with the hepatic ducts (Dh), form a network 

 from which three collecting ducts arise, and these unite to form the common 

 bile-duct (Dc) : the latter passes through the substance of the pancreas (P), 

 receiving further hepatic ducts (Dh 1 ), and the pancreatic ducts (P l ) ; at Dc 1 

 it becomes free from the pancreas, and passes back to open into the 

 duodenum (Dii) at Dc 2 ; G, gall-bladder ; L, L l , L s , the lobes of the liver 

 turned forwards ; Lhp, duodeno-hepatic omentum ; M, stomach ; Py, 

 pylorus. 



some Mammals). In some cases the ducts communicate with the 

 bile-duct 1 (Fig. 257). 



Varying much in form and size, the pancreas early gives rise to 

 a band-shaped or more or less lobulated and very vascular organ, 



1 The large digestive glands are said to appear ontogenetically in the 

 following order: 1, liver; 2, dorsal pancreas; 3, ventral pancreas. Phylo- 

 genetically the order is : 1, liver (Amphioxus, Cyclostomata) ; 2, liver and dorsal 

 pancreas (Elasmobranchii) ; 3, liver, and dorsal + ventral pancreas (most other 

 Vertebrates, including Amphibia, Sauropsida, and Mammalia). 



