308 THE ANATOMY OP TEETEBEATED ANIMALS. 



tary canal, tlie cardiac and pyloric apertiu-es of wldcli are 

 remote from one another ; but, in tlie Crocodiles, and in 

 most Bii-ds, tlie pyloric and cardiac apertures ai-e approxi- 

 mated. In many Crocodilia and Aves, there is a pyloric 

 dilatation before the commencement of the duodenum. 



In the Crocodilia, and in Aves, the walls of the stomach 

 ai'e veiy muscular, and the muscular fibres of each side 

 radiate from a central tendon or aponeurosis. The thick- 

 ening of the muscular tunic of the stomach attains its 

 maximum in the gi-aminivorous birds ; and it is accom- 

 panied by the development of the epithelium into a dense and 

 hard coat, adapted for crushing the food of these animals. 

 Birds commonly aid the triturating povrer of this gastric 

 mill by swallowing stones ; but this habit is not confined to 

 them, crocodiles having l^een observed to do the same thing. 



Bu-ds are further remarkable for the development of a 

 broad zone of glands in the lower part of the cesophagus, 

 which is usually dilated, and forms a proventriculus, 

 connected by a nan-ow neck with the above-mentioned 

 muscular stomach or gizzard (gigerium). 



Some Ophidia have a ccecum at the junction of the small 

 intestine with the lai-ge ; and two such cceca, which some- 

 times attain a large size, are very generally developed in 

 Aves. In this class also, the small intestine, not unfre- 

 quently, presenLs a coecal appendage, the remains of the 

 vitelline duct. The duodenum of Birds constantly makes 

 a loop, within which the pancreas lies, as in Mammalia. 



The liver in the Sauropsida almost always possesses a 

 gall bladder, which is usually attached to the under surface 

 of the right lobe, but in the Ophidia is removed to some 

 distance from it. 



A peculiar glandular sac, the Bursa Fahricii, opens into 

 the anterior and dorsal region of the cloaca in birds. 



Three forms of heart are found in the Sauropsida. The 

 fii'st is that observed in the Chelonia, Lacertilia, and Ophidia; 

 the second, that in the Crocodilia ; and the third, that in Aves. 



1. In the Chelonia, Lacertilia, and Ophidia, there are two 



