568 



REPTILIA. 



consists of three cavities, namely, a strong and muscular ventricle 

 (Jig- 256, a), and two membranous and very capacious auricles, 

 both of which communicate by valvular openings with the ventri- 

 cular cavity. The right auricle (b) receives the venous blood from 

 all parts of the body through the venae cavse (/, o,j?), the termina- 

 tions of which are guarded by strong valves ; the left auricle (c) 

 is appropriated exclusively to the lungs, from which it receives arte- 

 rial blood through the pulmonary veins (w, m). It is obvious, 

 therefore, that the ventricle receives two kinds of blood from the 

 two auricles, venous blood from the systemic auricle, and arterial 

 blood from the pulmonic auricle ; and as the interior of the ventri- 

 cular cavity is crossed by innumerable column earner, giving it 

 almost a spungoid appearance, the vitiated and purified blood derived 

 from these two sources are more or less completely mixed together, 

 and blood only partially arterialized is distributed to the system. 



Fig. 256. 



Two sets of vessels take their origin from the single ventricle, 

 viz. the pulmonary and aortic. The pulmonary artery soon di- 

 vides into two trunks (/,/), one destined to each lung ; so that a 



