VASCULAR SYSTEM OF LIZARD 



699 



Vascular system. — The heart is completely enveloped by 

 the pericardium, and is three-chambered, consisting of two 

 thin-walled auricles and a muscular ventricle. From the 

 ventral surface of the ventricle arises the conspicuous 

 truncus arteriosus, which is formed by the bases of the 

 aortic arches, and exhibits a division into two parts. From 

 the more ventral part arises the left aortic arch, which 

 curves round to the left side, first giving off a short connect- 



i^.a 



Fig. 410. 



-Heart and associated vessels of a lizard 

 — .A.fter Nuhn. 



A., 



Right auricle; jugulars (/.), subclaviaus (Set'.), and inferior 

 vena cava {I.V.C.) enter it. V., Ventricle ; tr., truncus arteriosus ; 

 I first aortic arch giving off carotids; 2, second aortic arch; 

 p.a., pulmonary artery; Sea., subclavian artery; Ao., dorsal 

 aorta. AA, Left auricle ; pulmonary veins (p.v.) enter it. In the 

 lizard described, the left jugular is not developed. 



ing vessel {ductus Botallii) to the carotid arch. From the 

 other division of the truncus arteriosus, a great arterial 

 trunk arises, and this gives off the right aortic arch and the 

 right and left carotid arches. The right aortic arch sends a 

 ductus Botallii to the carotid arch of the right side, and then 

 curves round the heart to join the left arch, the two thus 

 forming the dorsal aorta. The carotid arches supply the head 

 region with blood. From the base of the truncus arteriosus, 

 the right and left pulmonary arteries also arise (Fig. 410). 



