HEART OF REPTILES. 



>09 



335 



shape of the body, shows its greatest breadth, figs. 304, A, 335. 

 The two auricles, when distended, are of nearly equal size, and 

 of a subquadrate form, fig. 336, M, O. The bivalved orifice 

 between the sinus and the auricle, ib. 

 v, o, is a transverse slit. The white 

 arrow, o, shows the course of the blood 

 from the right auricle, past the valve 

 supported by the base of the auricu- 

 lar septum, into the aortic cavity of 

 the ventricle. In fig. 337 a bristle 

 passes through the orifice left by the 

 incomplete septum between the aortic 

 and pulmonic cavities into the latter, 

 which is the largest in JEmi/s, as in 

 Ophidia and Lacertilia : the bivalved 

 orifice of the pulmonary artery, r, is 

 shown. In fig. 338 that of the left aorta, 

 a, is similarly exposed, and the in- 

 complete septum is cut through : the 

 root of the right aorta, a', is behind 

 that of the left. The relative position 

 of the origins of the three arteries from the chelonian ventricle 

 is shown in fig. 336, where p is the pulmonary, a the left aorta, 

 a' the right aorta, the most posterior, or dorsal, of the three 

 arteries. The ventricle is almost wholly occupied by a spongy 

 muscular structure, and the cavities 



Heart of Tcstudo graeca 



are smaller in Testado than in Emys. 

 The left auricle, fig. 336, M, receives 

 the arterial blood from the lungs by 

 a single vein, the common trunk of the 

 pulmonary veins, ib. I, I: it opens into 

 the back part of the auricle near the 

 septum, and is guarded by a single 

 oblique membranous fold, ib. M. Each 

 auriculo-ventricular orifice is guarded 

 by a fold which extends across it from 

 either side of the base of the inter- 

 auricular septum ; to that of the left 

 auricle a small part of the muscular 

 structure is attached by chorda? tendineae. Opposite to the right 

 valve a semilunar ridge projects, in Testudo indica, which is the 

 rudiment of the second auriculo-ventricular valve in the Cro- 

 codile, and of the fleshy valve of that orifice in the right ventricle 



Structure of auricles : heart of Chclys 

 flmbriata 



