PHYLUM CHORDATA 



5°9 



visceral, immediately investing the heart. Between the two 

 is a narrow cavity containing a little fluid, the pericardial 

 fluid. In general shape the heart resembles that of the 

 pigeon, with the apex directed backwards and slightly to 

 the left, and the base forwards. Like that of the pigeon, it 

 contains right and left auricles and right and left ventricles, 

 the right and left sides of the heart having their cavities 

 completely separated off from one another by inter-auricular 

 and inter-ventricular partitions.- 



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Fig. 306. — Lepus CUniculUS. Heart, 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; /. pr. c, opening of pre-caval; 111 pap, musculi 

 papillares; pt.c, post-caval; pt. c , opening- of post-caval; r.prc, right pre- 

 caval; r. pul t right pulmonary artery; sew. v, semi-lunar valves; tri, tricuspid 

 valve. 



Into the right auricle open three large veins, the right 

 and left pre-caval veins and the single post-caval, the first 

 into the anterior part, the second into the left-hand side of 

 the posterior portion, and the third into the dorsal surface. 

 Projecting forwards from it is an ear-like auricular appendix. 

 On the septum is an oval area where the partition is thinner 



