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 Eeptiles 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 



A.vc 



Fig. 253. — Heart of A, Lacerta muralU, and B, 

 OF A Large Varo/iinn, i?Howx cfT opex ; C, 

 Diagram of the Reptilian Heart. 



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

 nate trunk ; 1, S, first and second arterial 

 arches ; Ap, Ap^, pulmonary arteries : Vjj, 

 pulmonary vein ; t and *, right and left 

 aortic arches ; RA, root of aorta ; Ao, dorsal aorta ; Ca, Ca^, carotids ; Asc, An, 

 subclavian arteries. /, jugular vein ; Vs, subclavian vein ; Ci, postcaval : 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, Vc, only one precaval being represented. 



the Anamnia.i 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 



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

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



