MARSUPIALIA. 



307 



separated from that of the anterior cava by a 

 simple crescentic ridge (e, figs. 131 and 132), 

 which forms a salient angle of the parietes of 

 the auricle between these apertures. The an- 

 terior cava (b) returns the blood from the right 

 side of the head and the right anterior extre- 

 mity; the corresponding vein on the left side 

 (c) passes down in all the Marsupials, as in 

 Birds and Reptiles, behind the left auricle, 

 below the two pulmonary veins, and, after 

 receiving the coronary vein, joins the inferior 

 cava (d) immediately before its expansion 

 into the auricle. 



F'IK. 132. 



Heart of the Wombat, 



Where the posterior extremities are less or 

 not larger than the anterior ones, as in the 

 Ursine Dasyure and Wombat, the posterior 

 cava is somewhat less than the left vena 

 innominata (Jigs. 131 and 132), and they 

 appear to terminate by separate apertures in 

 the auricle; but in the Kangaroo (Jig. 131) 

 the proportions of the two veins are reversed, 

 and the posterior cava more obviously receives 

 the left vena innominata before it terminates: 

 these two veins meet at a very acute angle, and 

 are separated by a crescentic ridge similar to, 

 but thinner than, that which divides their 

 common orifice from the orifice of the anterior 

 cava. 



The right auriculo-ventricular valve is mem- 

 branous, as in the placental Mammalia, and 

 its free margin is attached by fine chorda; ten- 

 dinese to three columns carnese ; these in the 

 Kangaroo (fig. 131) all arise from the septum 

 of the ventricles, but in the Wombat (fig. 132) 



the base of two of the columnse 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 ven- 

 tricle is continued in the form of a pyramidal 

 process, somewhat resembling a bulbtis arte- 

 riosits, to the origin of the pulmonary artery 

 (/> J*8 S ' 131 and 132), and projects beyond the 

 general surface of the heart further than in 

 ordinary Mammalia. 



The appendix of the left auricle is notched 

 in the Kangaroo to receive the apex of this pro- 

 cess, but not in the Wombat. Two pulmonary 

 veins (/,//#. 133) terminate close together, or by 

 a single trunk, at the upper and dextral angle 

 of this auricle. The mitral valve is regulated 

 by two short and thick columnar (k, k,Jig. 133), 

 which send their tendinous chords to the margin 

 and ventricular surface of the valve. 



Fig. 133. 



Heart of the Wombat. 



The ventricles and auricles present the usual 

 mammalian proportions and relative thickness 

 of their parietes. Three sigmoid valves are 

 situated at the origin of the pulmonary artery, 

 and the same number at that of the aorta. 



After the coronary arteries, the primary 

 branches from the arch of the aorta rise in 

 some species by three, in others by two trunks. 

 The broad-chested Marsupials, the Koala and 

 Wombat for instance, are those in which the left 

 carotid (g',fig- 132) and subclavian (h' ) arise 

 separately from the arch ; the arteria inno- 

 minata dividing into the right subclavian and 

 carotid (g, li, fig- 132), as in man. In most 

 of the other Marsupials the innominata give 

 off both carotids (g, g, Jig. 131) as well as the 

 right subclavian (It ) ; and the left subclavian 



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