522 THE RABBIT CHAP. 



prevent the valves from being pushed into the auricles 

 when the ventricles contract. 



The right ventricle narrows towards its base, on the 

 ventral side of the heart, to form a conical prolongation 

 from which arises the pulmonary artery (Figs. 135 and 

 140, p. a), its aperture being guarded by three pocket- 

 like, semilunar valves (Fig. 139, sem. v] : the aperture 



sem.v 



FIG. 139. Heart of the Rabbit, seen from the right side, the walls of the right auricle 



and right ventricle partly removed so as to expose the cavities, (x i.l.) 

 ao. aorta ; /. ov. fossa ovalis ; /. pr. c. opening of left precaval ; m. pap. papillary 

 muscles ; pt. c. postcaval ; pt. c'. opening of postcaval, with Kustachian valve 

 below ; r. pr. c. right precaval ; r. pul. right pulmonary artery ; sem. v. semi- 

 lunar valves at base of pulmonary artery ; tri. v. tricuspid valve. (From Parker 

 and Has well's Zoology.) 



of the aorta from the left ventricle is similarly provided 

 with three semilunar valves. The two precavals (I. pr. c, 

 r. pr. c) and the postcaval (pt. c) communicate, as we 

 have seen, directly with the right auricle, the right pre- 

 caval opening into it anteriorly, the left precaval 

 posteriorly, the aperture of the postcaval being just 

 anterior to that of the left precaval. The pulmonary 

 veins from each lung unite and open close together into 

 the left auricle. 



