. On the anatomy of vertebrates [electronic resource] . rge vesselsnear to the heart. The fibrous layer of the pericardium adheresto the sternum. The appendix of the right auricle is alwaysdivided into two angular processes, a, a, figs. 401 and 402, onein front and the other behind the trunk of the aorta, o. Theright auricle presents the following marsupial conditions:—Thereis no trace of a fossa ovalis or an 6 annulus ovalis,1 and theabsence of these structures, which are present in the heart of all 1 xx. vol. ii. p. 52. 518 ANATOMY OF VEETEBRATES. the placental Mammalia, relates to the very
. On the anatomy of vertebrates [electronic resource] . rge vesselsnear to the heart. The fibrous layer of the pericardium adheresto the sternum. The appendix of the right auricle is alwaysdivided into two angular processes, a, a, figs. 401 and 402, onein front and the other behind the trunk of the aorta, o. Theright auricle presents the following marsupial conditions:—Thereis no trace of a fossa ovalis or an 6 annulus ovalis,1 and theabsence of these structures, which are present in the heart of all 1 xx. vol. ii. p. 52. 518 ANATOMY OF VEETEBRATES. the placental Mammalia, relates to the very brief period duringwhich the auricles intercommunicate in the Marsupials, and tothe minute size, and in other respects incompletely developedstate, at which the young marsupial animal respires air by thelungs, and has the mature condition of the pulmonary circulationestablished. The right and left auricles intercommunicate by anoblique fissure in the uterine embryo of the Kangaroo whentwo-thirds of the period of gestation is past, but every trace of. Heart of the Kangaroo. Heart of the Wombat. this foetal structure is obliterated in the subsequent growth of theheart; so that in the mature animal the wide terminal orifice ofthe postcaval, ib. d, is separated from that of the right precaval,ib. b, by a simple crescentic ridge, ib. e, which forms a salient angleof the parietes of the auricle between these apertures. The orificeof the left precaval, ib. c, is close to that of the postcaval, in aposition analogous to that of the coronary vein in Man, whichhere opens into the left precaval. The right auriculo-ventricularvalve is membranous, and its free margin is attached by finee chordae tendineae to three mammillary ( columnaa carnea?; these HEART OF LISSENCEPIIALA. in the Kangaroo, fig. 401, arise from the septum of the ventricles,but in the Wombat, fig. 402, the base of two of the ( columnaris situated at the angle between the septum and the thin outerwall of the ventricle. The
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