MARSUPIALIA. 
rated 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 
(¢) 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. 
Fig. 132. 
. Heast 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 1s somewhat less than the left vena 
mnominata (figs. 131 and 132), and they 
appear to terminate by separate apertures in 
the auricle; but in the Kangaroo (fig. 131) 
the proportions of the two veins are reversed, 
and the posterior cava more obvious! y 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 
a orifice from the orifice of the anterior 
va. 
The right auriculo-ventricular valve is mem- 
branous, as in the placental Mammalia, and 
its free margin is attached by fine chorde ten- 
dine to three columnz carnez ; these in the 
Kangaroo (fig. 131) all arise from the septum 
of the ventricles, but in the Wombat (fig. 132) 
307 
the base of two of the columne 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 budbus arte- 
riosus, to the origin of the pulmonary artery 
Cf; figs. 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 (, fig. 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 columne (k, k, fig. 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, h, fig- 132), as in man. In most 
of the other Marsupials the innominata gives 
off both carotids (g, g, fig. 131) as well as the 
right subclavian (A); and the left subclavian 
x 
