MOLLUSCA 69 



they cross the pericardial cavity to reach the median 

 ventricle, into which they open, each by an aperture guarded 

 by a pair of valves. The ventricle by its pulsations propels 

 the blood into anterior and posterior aortae. The inner layer 

 of the pericardial cavity is involved in the contractions of the 

 ventricle and its cells are modified. The anterior aorta lies 

 along the dorsal aspect of the rectum and divides into arteries 



Ant. aorta Vent. Aur. Post, aorta 



Ext. eff. br. 



Aff. br. 



Int. eff. br. 



Vena cava 



Pedal art. 



Iff. renal 



Ext. eff. br. 



Pallial vein 



FIG. 33. Anodonta. Diagram of circulatory system. 



supplying the foot, digestive glands, stomach, and intestine, 

 as well as all the anterior part of the body. The posterior 

 aorta passes posteriorly from the ventricle on the under side 

 of the rectum and supplies that part of the intestine and the 

 neighbouring parts of the body. Both the aortae supply 

 blood to the mantle. In all parts of the body and mantle 

 the arteries split up into small arteries, and these are lost in 

 spaces or sinuses from which the blood is collected into veins. 

 The veins run into larger veins and ultimately, in the case of 

 the mantle, into the large paired pallial veins, and that of the 

 body generally into the paired, adposed venae cavae. Each 



