CHARACTERISTICS OF THE DIGESTIVE APPARATUS. 211 



crocodile, therefore, forms the connective link in the development of the 

 digestive tube between reptiles and birds. In this animal the duodenum 

 is also first seen, the liver and pancreas emptying into it, and the mesen- 

 tery first makes its appearance as a constant organ. The alimentary 

 canal of reptiles is simpler than that of birds, but resembles the bird 

 more than the fish. The oesophagus varies with the length of the neck, and 

 is wide and dilatable in the ophidia. It joins the stomach without' any 

 constriction, its mucous membrane becom- 

 ing glandular. In the serpents the cardiac 

 portion of the stomach is long, saccular, 

 and dilatable, while the pylorus is narrow 

 and muscular. The intestines are short 

 and wide in the carnivorous species, but 

 long and furnished with caeca in vegetable 

 feeders. 



Fig 



Fig. 69.— Stoji a ch of Crocodile. (Bymer Jones.) 



C. (Esophagus ; A. muscular fibres of stomach radiating from B, „,.,,. 



the central tendon, as in the gizzard of the bird ; D, commencement of &eca: Li large intestine; M 



duodenum. oviduct ; O, cloaca. 



-Digestive Apparatus op 

 Birds. 



A, ccsonhagus : B, crop; C, infundibulum ; 



D, gizzard ; E, liver ; F, gall-bladder : G, pan- 



H, duodenum; I, small intestine; K, 



ureters; N, 



In birds there is a most marked difference in the length and develop- 

 ment of their alimentaiy canal, dependent upon the nature of their food, 

 the granivorous and fructivorous birds having intestinal tubes of greater 

 length and complexity than those which live on animal diet (Fig. TO). 

 In all cases the stomach is well separated from the oesophagus, the 

 length of the latter being, of course, dependent upon the length of the 



