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, C, t and *) 

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



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

 OF A LARGE Varanus, SHOWN CUT OPEN ; C, 

 DIAGRAM OF THE REPTILIAN HEART. 



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

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

 Ap, Ap l , pulmonary artery ; Vp, pulmonary 

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

 root of aorta ; Ao, dorsal aorta ; Ca, Ca l , carotids ; Asc, As, 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 Vc, 

 Ve, 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, #), or of one 

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

 (Fig. 229, B, RA, 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. 



