REPORT ON THE MARSTJPIALIA. 151 



vein." l It appears to me that only one of these features can be considered as being a 

 universal distinction in the Marsupial heart, and that is the total absence of any land- 

 mark pointing back the early communication which exists between the auricles. In 

 TJnjlacine and Dasyure 2 there is not the slightest approach or tendency to a cleavage or 

 bifurcation of the appendix of the right auricle, and in all the animals I examined the 

 great cardiac vein {i.e., the vein which in the human heart expands into the coronary 

 sinus) entered the right auricle by an independent opening placed in the upper part of 

 the auricle by the side of the orifice of the right anterior vena cava. 



In Thylacinus (PI. IX. fig. 1) the heart is narrow, elongated and pointed. The right 

 auricle is very capacious, and its appendix, whilst it shows no indication of bifurcation, is 

 peculiar on account of its great breadth. On opening into the cavity of this auricle we 

 notice that the walls of the appendix alone present musculi pectinati. The walls of the 

 atrium are perfectly smooth and even. In addition to the minute apertures of the venae 

 Thebesii, and the small mouths of a few anterior cardiac veins which open directly into 

 the auricle, there are four large venous openings — two in front, and two behind. Those 

 in front are the orifice of the right anterior vena cava (which has the same position as 

 that of the superior vena cava in man), and the orifice of the great cardiac vein which hes 

 at a slightly lower level, and to its inner side. The latter presents a gaping mouth 

 towards the cavity, and both are totally destitute of valves. The two posterior openings 

 are (l) that of the posterior vena cana which has the usual situation, and (2) the opening 

 of the left anterior vena cava which is placed between the orifice of the posterior vena 

 cava, and the auriculo-ventricular opening, — it occupies, therefore, the same position 

 as the coronary aperture in the human heart. The auriculo-ventricular opening readily 

 allows two fingers to be passed through it into the cavity of the right ventricle. 



Right ventricle. — The cavity of the right ventricle falls short of the apex of the heart 

 by fully an inch and a half. The conus arteriosus is very pronounced. In the interior 

 of the ventricle the columnse carnese are scarce and are altogether absent in the conus 

 arteriosus, and at the apex of the cavity. The musculi papillares are disposed in two 

 groups, viz., one upon the septum near its anterior margin, and the other upon the 

 anterior wall of the ventricle near the right sharp margin of the heart. In connection with 

 each there is a moderator band. That passing from the base of the septal muscle to the 

 anterior wall is very delicate, whilst the other, which stretches between the base of the 

 anterior muscle and the septum, is remarkably strong. Indeed, we might look upon the 

 anterior musculus papillaris as arising by two equal parts, one from the septum, and the 

 other from the anterior wall. 



1 Notes on the Anatomy of the Wombat (Proc. Zool. Soe. 1836, p. 51) ; Comparative Anatomy ami Physiology of 

 Vertebrates, vol. iii. p. 517 ; Cyclopedia of Anatomy and Physiology (Marsupialia), vol. iii. p. 306. 



" In his paper upon Dasywrus macrurus (Proc. Zool. Soc, 1835, p. 8) he makes no reference to a bifurcated condition 

 of the right auricle. He only says — "The right auricle rose high above the left. Both auricles had smooth short 

 appendices." 



