396 



MANUAL OF ZOOLOGY. 



between the ventricles a perfect one, and even in these, as in 

 all other Reptiles, the heart consists functionally of no more 

 than three chambers. The ordinary course of the circulation, 

 where the ventricular septum is imperfect, is as follows : The 



impure venous blood returned 

 from the body is, of course, 

 poured by the venae cavse into the 

 right auricle (fig. 154, a), and 

 thence into the ventricle. The 

 pure arterialised and aerated 

 blood that has passed through 

 the lungs, is equally, of course, 

 poured into the left auricle (a'), 

 and thence propelled into the 

 ventricle (v). As the ventricular 

 cavity is single, and not divided 

 by a complete partition, it fol- 

 lows of necessity that there is a 

 mixture in the ventricle, resulting 

 in the production of a mixed 

 fluid, consisting partly of venous 

 and partly of arterial blood. 

 This mixed fluid, then, occupies 

 the common ventricular cavity, 

 and by this it is driven both to 

 the lungs (through the pulmonary 

 artery), and to the body (through 

 the systemic aorta). Conse- 



Fig. 154. Diagram of the circulation in ^.,^^4-U. "D^T^I^c "hr^li fViA 



Reptiles. (The venous system is left quently, in KeptllCS, _ DOtll me 



light, the arterial system is black, and JungS and the VaHOUS tlSSUCS and 



the vessels containing mixed blood are r , , , -, i J 



cross-shaded.) a Right auricle, receiv- organs of the body are supplied 

 ing venous blood from the body ; a' w [ t ^ a m i x ture of arterial and 



Left auricle, receiving arterial blood 



from the lungs ; v Arterio-venous ven- VCnOUS blOOQ, and not With Un- 



tricle, containing mixed blood, which is ^iv^rl KlnoH fhf> InncrQ wirh 



driven by (/) the pulmonary artery to mix eO- DlOOQ- 



the lungs, and by (o) the aorta to the purely venous, and the body with 



purely arterial blood as is the 



case with the higher Vertebrata. In the Crocodilia, as before 

 said, the partition between the ventricles is a complete one, 

 and consequently this mixture of the arterial and venous blood 

 cannot take place within the heart itself. In these Reptiles, 

 however, a direct communication exists between the pulmonary 

 artery and aorta (the right and left aortas) by the so-called 

 " foramen Panizzae," close to the point where these vessels 

 spring respectively from the right and left ventricle. In these 

 Reptiles, therefore, the same mixture of arterial blood with 



