VASCULAR SYSTEM UROGENITAL ORGANS. 203 



ventricle or ventricles, and not one only as in the Ichthyopsida]. 

 In the Snakes and Lizards the left arterial trunk is prolonged 

 into the left aortic root without giving off vessels (fig. 60, Aos], 

 while the right and larger before being prolonged into the 

 right aortic root gives off" a common stem for the two carotids 

 (fig. 60, I), between which and the corresponding aortic roots a 

 connecting vessel (ductus Botalli), constituting a second persistent 

 aortic arch, may be retained (many Lizards). In the Chelonia the 

 right aortic arch likewise gives oft* the carotids and subclavians, while 

 the left gives off the visceral arteries. In consequence of the very 

 small size of the aortic root of the latter, the aorta appears to be 

 mainly a pi'olongation of the right aortic arch. Crocodiles present 

 the same arrangements, but in them the right arterial trunk arises 

 from the left ventricle and receives arterial blood from the latter. 

 In this case also, in spite of the complete division of the heart, the 

 mixture of venous and arterial blood is not wholly avoided, since 

 there is a communication the foramen Panizzce between the right 

 and left aortic arches. When the separation of the two ventricles is 

 incomplete, mixture of the two kinds of blood takes place in part in 

 the heart, although the entrance into the pulmonary vessels can by 

 special valvular arrangements be separated from the ostia of the 

 arterial trunks in such a manner that the arterial blood principally 

 flows into the latter, and the venous into the former (Briicke). In 

 the venous system there is, as in the Amphibia, a renal-portal as 

 well as an hepatic-portal circulation^. In the Chelonia and Crocodilia, 

 however, the renal-portal system is more and more reduced, for the 

 greater part of the blood of the iliac veins passes to the liver. The 

 system of lymphatic vessels presents extraordinarily numerous and 

 wide lymph spaces, and is arranged exactly like that of the Amphibia. 

 Contractile lymph hearts have only been discovered in the posterior 

 part of the body at the junction of the trunk and tail. They 

 are paired and situated 011 the transverse processes or ribs. 



The kidneys of Reptiles belong, as in Birds and Mammals, to the 

 hinder region of the trunk, and correspond accordingly only to the 

 posterior broad part of the Amphibian kidney. In Lizards and 

 Chelonians a urinary bladder projects on the anterior wall of the 

 cloaca, The urine is not by any means always fluid, but is often a 

 whitish mass of firm consistency, and contains uric acid. 



The generative organs (fig 634) resemble those of Birds. The 

 morphological relations of the generative organs of the higher 

 vertebrates are attained, inasmuch as the anterior region of the 



