522 THE RABBIT CHAP. 



(m. pap) : these serve to 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.d), its aperture being guarded by three pocket-like, semi- 

 lunar valves (Fig. 139, sem. v) : the aperture of the aorta from 



sem,.?/ 



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. 

 ao. aorta \f.ov, fossa ovalis ; l.pr.c. opening of left precaval ; m.pap. papillary 

 muscles ; pt. c. postcaval ; pt. c'. opening of postcaval ; r. pr. c. right pre- 

 caval ; r. pul. right pulmonary artery ; sem. v. semilunar valves at base of 

 pulmonary artery ; tri. v. tricuspid valve. (From Parker and Haswell's 

 Zoology. ) 



the left ventricle is similarly provided with three semilunar 

 valves. The two precavals (/. pr. c, r. pr. c) and the post- 

 caval (pt. c} communicate, as we have seen, directly with 

 the right auricle, the right precaval 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 together 

 into the left auricle. 



