THE HEART AND CIRCULATORY SYSTEM 



115 



pumps blood into the right ventricle which communicates with 

 both the pulmonary and left systemic arches. A feature which is 

 peculiar to the crocodile heart is found shortly after the two 

 systemic arches have arisen from the two ventricles. In this 

 region there is a smsdl foramen ofPanizza. 



The differences between various extant reptiles are not sur- 

 prising when it is remembered that they are derived from stocks 

 which have been separate for a very long time. The crocodile 

 heart is of particular interest because it is easy to derive that of 



(a) 



CROCODILE 



(b) 

 BIRD 



Right 

 pulmonary 



Right 

 systemic 



Left 



carotid 



Left 



pulmonary 



artery 



Fig. 34. 



Ventral views of the hearts of (a) a crocodile, and (b) a bird. 



birds from it. Thus from fig. 34 it is clear that closure of the fora- 

 men ofPanizza, together with the loss of the left systemic, would 

 lead to a complete double circulation which would be funda- 



