264 THE ANATOMY OF VERTEBRATED ANIMALS. 



by a narrow neck with the above-mentioned muscular stomach 

 or gizzard [gigeriuni). 



Some Oj^hidia have a caecum at the junction of the small 

 intestine with the large ; and two such cseca, Avhich sometimes 

 attain a large size, are very generally developed in A.ves. In 

 this class also, the small intestine, not unfrequently, presents 

 a cfiecal 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 Saurojjsida almost always possesses a 

 gall-bladder, which is usually attached to the under surface 

 of the right lobe, but in the 02:)hidia is removed to some 

 distance from it. 



A peculiar glandular sac, the JBursa Fahricii., opens into 

 the anterior and dorsal region of the cloaca in birds. 



Three forms of heart are found in the Sauropsida. The 

 first is that observed in the Ghelonia^ Lacertilia^ and Ojyhidr 

 ia y the second, that in the Crocodilia / and the third, that 

 in Aves. 



1. In the Chelo7iia, JLacertilia^ and Ophidia, there are 

 two auricles. Generally, a distinct shius venosus, with con- 

 tractile walls, and communicating b}^ a valvular aperture with 

 the auricle, receives the blood from the ve7i(ie cavce, and pours 

 it into the right auricle. The pulmonary veins usually open 

 by a common trunk into the left auricle. 



The interauricular septum is rarely (in some CJielonia) 

 perforated. Its ventricular edge spreads out on each side into 

 a broad membranous valve, the edge of w^hich, during the 

 systole, flaps against a ridge, or fold, developed, on one, or 

 both sides, from the margin of the auriculo-ventricular aper- 

 ture, and constituting a rudiment of a second valve. The 

 ventricle contains only one cavity, but that cavity is im- 

 perfectly divided into two or three chambers, by septa devel- 

 oped from its muscular walls. 



In the Turtle (Fig. 92), a partly muscular, and partly carti- 

 laginous, septum extends from the front wall of the ventricular 

 ca\aty toward its right-hand end. It imperfectly divides the 

 common ventricular cavity into a right small, and a left large^ 

 moiety. The latter of these receives the blood from the auri- 

 cles. In consequence of the elongated form of the ventricular 

 cavity, and the projection into it of the large auriculo-ven- 

 tricular valves, especially of that of the right side, this left and 

 larger moiety of the common ventricle is virtually divided into 



