224 



COMPARATIVE MORPHOLOGY OF VERTEBRATES. 



oesophagus usually extends a short distance into the body cavity and 

 then its lower end has the same coat. 



The true stomach is characterized by the presence of glands, de- 

 veloped from the mucous layer and emptying into the lumen. Of 

 these glands there are at most (mammals) three kinds: cardiac, near 

 the entrance of the oesophagus, which secrete an albuminoid fluid; 



FIG. 227. Different shapes of stomachs, mostly after Nuhn (Keibel). a, Belone; b, 

 Proteus; c, Tropidonotus natrix; d, Gobius; e, shark; f, Phoca vitulina; g, Polypterus; h, 

 Fulica atra; i, Testudo graca; k, land tortoise; /, rabbit; m, pig; n, owl; o, crocodile; p, 

 Delphinus; q, Halmaturus. 



pyloric, near the pylorus, which form mucus; and the most character- 

 istic, the fundus glands, which secrete a digestive ferment, pepsin. 

 (For the structure of these glands reference should be made to histological 

 text-books.) Tested by glands, many vertebrates (dipnoi, cyprinoids) 

 lack a true stomach, while the sturgeons have the gastric glands extend- 

 ing into the oesophagus. On the other hand, a part of the enlargement 

 called the stomach in mammals often includes a part of the oesophagus 

 (fig. 228, A, E). 



