272 



COMPARATIVE ANATOMY 



of two lobes as the primary one in all Vertebrates. The liver of 

 the Anamnia is usually relatively larger than that of the Amniota. 



Carnivorous (fat-eating) animals generally possess a larger liver than 

 Herbivores. 



A gall-Madder 'is very commonly present partially imbedded in 

 the right primary lobe. It is connected with the system of hepatic 



FIG. 218. A, B, C, VARIOUS MODIFICATIONS IN THE ARRANGEMENT OF THE 



BILE-DUCTS. 



D, duodenum ; Vf, gall-bladder ; c and .<?, cystic duct ; h, hepatic duct ; ch, 

 common bile-duct ; Ac, hepato-cystic duct ; he, hepato-enteric duct. 



ducts by means of a cystic duct, thus forming a common bile-duct 

 which opens into the anterior part of the intestine (duodenum). 

 Some of the chief variations in the relative arrangement of these 

 ducts are shown in Fig. 218. 



PANCREAS. 



The pancreas arises from the proximal portion of the small in- 

 testine, near the liver, in the form of several (usually two dorsal 

 and one ventral) independent endodermic outgrowths : these may 

 become fused later, or certain of them may undergo degeneration. 

 Thus in the adult there may be a single duct, or several inde- 

 pendent ducts opening into the intestine (e.g., Birds, Crocodiles, 

 Emydse, and some Mammals) or in some cases into the bile-duct 

 (Fig. 216, B). Varying much in form and size, the pancreas early 

 gives rise to a band-shaped or more or less lobulated organ, usually 

 lying in the fold of the duodenum. In some cases it remains em- 

 bedded within the wall of the gut (e.g., Protopterus, 1 Fig. 209), and 

 amongst Teleosts (in which Order the pancreas was formerly sup- 

 posed to be absent in the adult) it may be surrounded by the liver 

 or have the form of scattered lobules extending throughout the 

 mesentery. 



1 In Myxinoids a lobular gland is present in a similar relative position to the 

 pancreas of Protopterus in the neighbourhood of the bile-duct, into which it 

 opens : this probably corresponds to a pancreas. A dorsal pancreas is also de- 

 veloped in the embryo of Petromyzon, and a pancreas-like organ can be recognised 

 in the adult. The pancreas is not represented in Amphioxus. 



