THE HEART AND CIRCULATORY SYSTEM 



113 



shows the complexity of these hearts, for both auricles open into a 

 single ventricular chamber which corresponds to the left ven- 

 tricle but is dorsal in position. The main septum is nearly hori- 

 zontal and incomplete anteriorly. The larger dorsal chamber 

 extends posteriorly and it is into this that the two auricles open 

 and from which arise the two systemic arches. The dorsal 

 chamber communicates with the smaller ventral chamber (cavum 

 ventrale) via the edge of the incomplete septum and this is the 

 route of all blood which enters the pulmonary arteries, as they 

 arise from the ventral chamber. The course of the blood deduced 

 from a morphological study of the aortic arches suggests that the 



Right 

 systemic 



Right 

 pulmonary 



Right 

 auricle 



Horizontal 

 septum 



Subclavian 

 artery 



Internal 

 carotid 



(b) 



VENTRAL 

 Pulmonary artery 

 Ductus ^^sds off from 

 caroticus ventral chamber 



Left 

 systemic 



Horizontal 

 septum 



Left systemic , , . , . . 



/ Dorsal Left-auriculo- 

 Right system^ n^^e ventricular 



DORSAL 



Fig. 33. 



The heart oiLacerta viridis. (a) Ventral view showing the ventricle 

 opened up and the path of the blood from the auricles to the different 

 aortic arches, (b) Transverse section through the ventricle just behind 

 the openings from the auricles. The relative positions of the auriculo- 

 ventricular valves and of the origin of the three arches are shown as 

 seen from behind and looking forwards to the anterior part of the 

 ventricle. Oxygenated blood in full lines; deoxygenated blood in 

 dotted lines. 



