X HEART 505 



(ni. pap) : these serve tu jjrevent 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 piilmonarv arterv (Figs. 125 and 130, 

 /.(!), its aperture being guarded by three pocket-like, semi- 

 lunar valves (Fig. 129, sein. v) : the aperture of the aorta from 



i.iJurj 



Fig. \'^r). — I kail •}{ tlic rabljit, sei^ii fiuiii Lht riglit sidu, tlic walls of Llic riglil aiiriclu 

 and right venlriclc partly removed so as tu e.\pose the cavities. 

 ao. aorta \ /. ai'. fossa ovalis ; /./;-. t". opening of left precaval ; ///./rt/. papillary 

 muscles; ^t.c. postcaval; pt.c'. opening of postcaval: r. J>r. c. right pre- 

 caval ; r. /;//. right pulmonary artery : sent. 7'. semilunar valves ; tH. i'. 

 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 (//. (■) communicate, as we have seen, directly with 

 the right auricle, the right precaval oi^ening into it anteriorh', 

 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. 



