452 ANATOMY OF VERTEBRATES. 



receptacle and ducts is obvious. Had the gall-bladder been 

 attached to the liver, as in insectivorous Anguidce and Lizards, 

 it would have been compressed by the prey, which in true 

 Serpents is usually of large bulk when introduced into the 

 stomach. The stimulus of such pressure would have led to the 

 expulsion of the contents of the gall-bladder into the intestine 

 before the chyme had been prepared, and passed on into the 

 gut : the relative position of the liver to the stomach subjects 

 the ofland to such stimulus to secrete whilst the contents of the 



o 



distended stomach are undergoing digestion. The bile is con- 

 veyed away by the long hepatic duct, but is reflected along 

 the branching cystic ducts to the gall-bladder, which has been 

 transferred to a position beyond the pressure of the stomach. It 

 is so placed, however, as to be affected by the distension of the 

 narrow canal which conveys the chyme to the duodenum, and is 

 thus stimulated to render up the bile to the gut, just at the time 

 when it is wanted for the separation of the chyle from the chyme. 

 This fact in comparative anatomy is significant of the share taken 

 by the biliary secretion in the act of chylification. 



The gall-bladder is not, however, a simple reservoir ; its vascular 

 and secreting inner surface can operate upon the bile by both 

 subtraction and addition : the more watery part may be diminished 

 by absorption : the cylindrical epithelial cells which form the 

 innermost layer of the mucous membrane may be shed into the 

 liquid, with the contents of mucous follicles which are more or 

 less developed in that membrane. The mucous surface is 

 augmented by minute furrows in the Crocodile : in the Testudo 

 elephantopus it is nearly smooth. 



The bile in Chelonia and most Reptiles is green : Hunter 

 notices its pale yellow colour in the f Water-snake,' and its want 

 of bitter taste in the Chameleon. 1 Chemical researches on the 

 nature of bile have been almost exclusively confined to that of 

 Mammals, in connection with which class the chief results will 

 be noted. The glycocholic acid is wanting in the bile of the 

 Boa, as in that of the Dog. As might be supposed, from the 

 prevalent colour of the bile in Reptiles, the f biliverdine' primarily 

 exists in it, not as a transformation of ( cholepyrrhine,' which is 

 the primary colouring principle in most Mammals. The propor- 

 tion of taurocholate of soda in the bile of a Python is estimated 

 at 8 -46 in 100, and in that of a Boa to 6*2 in 100 ; a trace of the 

 same principle has been detected in the bile of a Tortoise. In 



1 ccxxxvi. vol. ii. pp. 373, 378. 



