HEART 



409 



made up at its origin of two arches, anastomosing with one 

 another (Lacerta, Fig. 310, A), or of one only (certain Lizards, 

 Snakes, Chelonians, and Crocodiles, Figs. 310, B, 312), from which 

 the carotid artery arises directly. The left and right aortic arches 



J).C.S 



m^m 



A. 



FIG. 31-2. 



FIG. 313. 



FIG. 31'2. HEART OF A YOUNG L'rovodilun itiloticiis. From the dorsal side. 



(After Rose.) 



A<1 and ^4*, right and left aortic arches; A.m, mesenteric artery; L.V.li, 

 K. V.h, left and right atria; S.d, S.s, subclavian arteries; Tr.<:c, common 

 carotid ; V.c.c, coronary vein. Other letters as in Fig. 311. 



FIG. 313. HEART OF Crowlilux nil ot If us. From the right side. (After Rose.) 

 Part of the wall of the right atrium is removed. 



O.a.v, atrio- ventricular aperture ; Va.d and Va.x, the two sinu-auricular valves, 

 the white line between which is the margin of the septum sinus venosi. Other 

 letters as iri Figs. 311 and 312. 



cross at their base, so that the left arises on the right side, and 

 vice versa. The most posterior arterial arch gives rise to the 

 pulmonary artery (cf. Fig. 301, D). 



The blood from the right ventricle passes into the pulmonary 

 artery as well as into the left aortic arch, and, according as the 



