THE HEART AND ITS VESSELS. 



285 



Amphibian heart is seen in the appearance of a ventricular 

 septum, which may be incomplete, as in Lizards, Snakes, and 

 Chelonians, or complete, as in Crocodiles. 1 



A right and left aortic root or arch (Fig. 229, 0, t and *) 

 are always present, and unite to form the dorsal aorta. Each 



B 



FIG. 229. A, HEART OF Laccrta muralis, AND B, 

 OF A LARGE Varanus, SHOWN CUT OPEN ; C, 

 DIAGRAM OF THE REPTILIAN HEART. 



V, y 1 , ventricles ; A, A 1 , atria ; tr, Trcn, innonii- 

 nl i nate trunk ; 1, 2, first and second arterial arch ; 



Ap, Ap 1 , pulmonary artery ; Vp, pulmonary 

 vein ; t and *, right and left aortic arch ; RA, 

 root of aorta ; Ao, dorsal aorta ; Ca, Ca 1 , carotids ; Asc, As, subclavian arteries ; J, 

 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 Vc, 

 Vc, only one precaval being represented. 



aortic root may be made up at its origin of two arches, anas- 

 tomosing with one another (Lacerta) (Fig. 229, A, 1, 2), or of one 

 only (certain Lizards, Snakes, Chelonians, and Crocodiles) 

 (Fig. 229, B, HA, RA}. The most posterior arterial arch gives 

 rise to the pulmonary artery (Ap) (comp. also Fig. 221, A, B). 



1 A small aperture of communication between the ventricles, the foramen 

 Panizzae, exists in Crocodiles. Near it, between the origin of the left aorta and the 

 pulmonary artery, there is a small cartilage, as in Chelonians. 



