CiU 



ANATOMY OF VERTEBRATES. 



continues to be the seat of progressing devclopcmcnt, and coil 

 after coil of intestine is formed between the duodenum before, 

 and the rectum behind the primitive simple vitelline sac, the 

 coils being disposed in a close double spiral, fig. 433, I. Thus, 

 the fully developed larva is provided with an alimentary canal, 



433 



Diagram of the anatomy of the Tadpole. 



adapted, by its length and complexity, for the assimilation 

 of the decaying vegetable matters which chiefly constitute its 

 food. In the conversion of this digestive apparatus into that 

 of the purely carnivorous Frog, the horny cutaneous beak is 

 changed into a wide mouth formed by well-ossified jaws, the 

 lower one armed with sharp teeth. The branchial pharynx is 

 contracted and closed at the sides, except where it communicates 



with the ears. The oesopha- 

 gus and stomach are elong- 

 ated ; the intestine is marvel- 

 lously shortened ; the rectum 

 contracts, and is found to 

 open, after the absorption of 

 the tail and cutaneous anal 

 fold, just in front of the 

 symphysis pubis, now com- 

 pleted by the developement 

 of the hind limbs. Whilst 

 the heart, as a bent tube, fig. 

 434, f, sends off the branchial 

 arteries from its fore part, it 

 is connected behind with ves- 

 sels ramifying on the vitel- 

 licle, ib., b : a portion of this 

 is soon seen to be marked 

 off from the rest, as the 

 basis of the future liver and pancreas. 



1 cccxxvni. 



Tadpole of Toad, magn. cxxii. 



