VASCULAR SYSTEM 



313 



obliterated, and there is no ductus Botalli : the other vessels re- 

 semble those of the Salamander. In lungless forms (p. 290) a 

 correlative reduction of the pulmonary vessels occurs. 



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 much further back than is the case in 



FIG. 253. HEART OF A, Lacerta muralis, AND B, 

 OF A LARGE Varanus, SHOWN CUT OPEN ; C, 

 DIAGRAM OF THE REPTILIAN HEART. 



V, V 1 , ventricles ; A, A\ atria ; tr, Trca, innomi- 

 nate trunk ; 1, 2, first and second arterial 



HA W **"** arches ; Ap, Ap l , pulmonary arteries ; Vp, 



pulmonary vein ; t and *, right and left 



aortic arches ; RA, root of aorta ; Ao, dorsal aorta ; Ca, Ca l , carotids ; Asc, A$, 

 subclavian arteries. /, jugular vein ; V#> subclavian vein ; Ci, postcayal : these 

 three veins open into the sinus venosus, which lies on the dorsal side of the 

 heart, above the point indicated by the letter S. In the diagram C the pre- and 

 postcavals are indicated by Ve, Ve, only one precaval being represented. 



the Anamnia. 1 The carotid arteries and jugular veins are thus 

 correspondingly elongated. 



The principal advance in structure as compared with the Am- 

 phibian heart is seen in the appearance of a muscular ventricular 



1 It is situated furthest forwards in the majority of Lizards and in Chelonians : 

 in Amphisbienians, Snakes and Crocodiles it lies much further back. 



