HEART OF LISSENCEPHALA. 



519 



in the Kangaroo, fig. 401, arise from the septum of the ventricles, 

 but in the Wombat, fig. 402, the base of two of the ' columnge ' 

 is situated at the angle between the septum and the thin outer 

 wall of the ventricle. The right ventricle extends nearly to the 

 apex of the heart in the Wombat, but falls short of that part in 

 the Kangaroo. The ventricle is continued in a conical form, 

 somewhat resembling; a ' bulbus arteriosus,' to the origin of the 



o ~ 



pulmonary artery,/, figs. 401 and 402, and projects beyond the 

 general surface of the 403 



heart further than in or- 

 dinary Mammalia. The 

 appendix of the left au- 

 ricle is notched in the 

 Kangaroo to receive the 

 apex of this process, but 

 not in the Wombat. Two 

 pulmonary veins, i, fig. 

 403, terminate close to- 

 gether, or by a single 

 trunk, at the upper and 

 dextral angle of this au- 

 ricle. The mitral valve 

 is regulated by two short 

 and thick mainmillary 

 columns, ib. k, k, which 

 send their tendinous 

 chords to the margin 

 and ventricular surface 

 of the valve. 



The ventricles and 

 auricles present the usual Mammalian proportions and relative 

 thickness of the parietes. Three sigmoid valves are situated at 

 the origin of the pulmonary artery, and the same number at that 

 of the aorta. 



B. Heart of Lissencephala. In most species of this subclass 1 

 the right auricle shows the modifications resulting from the return 

 of the blood thereto, as in Lyencephala, by two distinct precavals, 

 of which the left opens alongside the postcaval into the lower 

 (sacral) part of the auricle, as in figs. 401, 402. In the Por- 

 cupine a large ( Eustachian ' fold is on the auricular side of the 



1 Capromys is an exception, among the Rodents : at least in the specimen I dis- 

 sected, the blood from the head and fore-limbs entered the auricle by a single precaval 

 vein. cxxx". p. 72. 



Heart of the Wombat. 



