HEART 



407 



only, there being no direct anastomoses. The consequence of this 

 is that all the blood becomes oxygenated. In the adult Frog 

 the third arterial arch is entirely obliterated, and there is no ductus 

 Botalli : the other vessels resemble those of the Salamander. 



Reptiles. As in all Amniota, the heart of Reptiles arises far 

 forwards in the neighbourhood of the gill-clefts, but on the forma- 

 tion of a neck it comes to lie relatively further back than in the 



R4- 



FIG. 310. HEART OF A, Lacerta muralis, AND B, A 

 LARGE Varanus, SHOWN CUT OPEN ; C, DIAGRAM 

 OF THE REPTILIAN HEART. Ventral view. 



A, A 1 , atria ; Ao, dorsal aorta ; Ap, Ap 1 , pulmonary 

 arteries ; Asc, As, subclavians ; Ca, Co 1 , carotids ; 

 Ci, postcaval : /, jugular; RA, root of aorta; 

 tr, Trca, innominate ; Vp, pulmonary vein ; Vs, subelavian vein ; T", T 71 , ven- 

 tricles ; 1, 2, 1st and 2nd arterial arches ; t, *, right and left aortic arches. 

 In C, the pre- and postcavals are indicated by Ve, Ve, only one precaval being 

 represented. A fibrous cord connects the apex of the ventricle with the peri- 

 cardium in most Lizards. 



RA 



Anamnia, and this is more especially the case in AmphisbaBnians, 

 Snakes, and Crocodiles.- The carotid arteries and jugular veins 

 are thus correspondingly elongated. 



The sinus venosus, which even in the Amphibia especially 



