348 



COMPARATIVE ANATOMY 



system, which has a very specific arrangement in the liver and 

 shows a divergent mode of development in passing towards 

 Amphibians and Reptiles on the one hand, and Mammals on the 

 other. 



The liver is connected with the body- wall by folds of the peri- 

 toneum, and the differences which are seen in its form are due to 

 the fact that it becomes more or less closely adapted to fit against 

 and between the neighbouring organs (stomach, intestine, &c.), and 

 as regards the formation of lobes, to its close relations with the 

 portal and hepatic veins and (in Mammals) to the diaphragm. 



FIG. 256. A, B, C, VARIOUS MODIFICATIONS IN THE ARRANGEMENT OF THE 



BILE-DUCTS. 



c and s, cystic duct ; ch, common bile-duct ; D, duodenum ; h, hepatic duct ; 

 he, hepato- cystic duct ; he, hepato-enteric duct ; Vf, gall-bladder. 



The number of lobes varies, and in Mammals (e.g. Carnivores) 

 there may be as many as six or seven. 



The function of this large and vascular organ consists, in the 

 first instance, in the secretion of bile, but it has a further importance 

 in connection with the formation of glycogen, urea, &c. It is con- 

 nected with the lumen of the anterior part of the intestine by 

 means of one or more bile-ducts, an offshoot from which may 

 become enlarged and give rise to a receptacle, the gall-bladder. 

 The duct from this is known as the cystic duct : it is connected in 

 various ways with the system of hepatic ducts from the liver, and 

 thus may form a common bile-duct opening into the intestine 1 

 (Figs. 256, 257). 



PANCREAS. 



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

 testine, uear the liver, in the form of several independent endo- 



1 On the metamorphosis of the ammoccete-larva of the Lamprey, the single- 

 lobed liver, like the intestine, undergoes a peculiar modification and partial 

 degeneration. It is at first of a typical tubular structure, and possesses bile- 

 ducts and a gall-bladder ; the bile-capillaries, ducts, and gall-bladder gradually 

 disappear, and at the same time the blood-capillaries become enlarged and more 

 completely surround the cell-trabeculas, so that a change of function probably 

 occurs. 



