REPORT ON THE MARSUPIALIA. 153 



Right auricle. — The cavity of the right auricle presents the same characters as those 

 noticed in Thylacine and Dasyure. The opening of the great cardiac vein, however, is 

 very difficult to find, as it is hidden by musculi pectinati. 



Right ventricle. — The cavity of the right ventricle shows several points of difference. 

 The columnae carneae are confined almost entirely to the anterior wall. The musculi 

 papillares are two in number, and both spring from the septum. They are long and 

 slender, and one is situated near the anterior interventricular furrow, whilst the other 

 takes origin close to the right sharp margin of the heart. A complete chain of " moder- 

 ator bands " extends downwards from the conns anteriosus to the apex of the cavity, 

 and binds the anterior wall firmly to the septum. Those which are highest are so large 

 that they even exceed in size the musculi papillares, but they gradually diminish as they 

 are traced downwards to the apex. 



The right auriculo-ventricular valve presents four separate membranous segments. 

 These cusps are arranged so that two are placed anteriorly, one to the right, and the 

 fourth, much larger than the others, posteriorly against the septum. The first three of 

 these are connected by chordae tendineae, with the musculi papillares; the large posterior 

 cusp is bound down by short, strong tendinous cords which take origin from the septum. 

 It therefore possesses a very limited range of movement. 



Left auricle. — The cavity of the left auricle differs from that in Thylacine, in having 

 its appendicular walls smooth except towards its free margin, where it shows the reticular 

 arrangement of musculi pectinati. 



Left ventricle. — In the left ventricle, the columnae carneae are something marvellous 

 in their intricacy and delicacy. . . 



The heart of the Vulpine phalanger closely resembles that of the Cuscus. The notching 

 of the right auricular appendage is quite as strongly marked, and the only points of difference 

 are found in the right ventricle. Here there are four musculi papillares, all of which 

 spring from the septum and all of which are connected with the three small cusps of the 

 right auriculo-ventricular opening. The large posterior cusp, as in Cuscus, is bound 

 directly by chordae tendineas to the septum. Further, the moderator bands are neither 

 so distinct nor so numerous. 



In the Phascogale we note the following points: — (1) the right auricular ap- 

 pendage shows a slight trace of notching, but this has no relation to the root of the 

 aorta; (2) a slight notching of the left auricular appendage is also observable; (3) the mus- 

 culi papillares are two in number in the right ventricle, and both arise from the septum. 



It would appear, therefore, that the distinguishing features of the marsupial heart are 

 two in number, viz. — (1) the absence of all trace of an annulus ovalis and a fossa ovalis, 

 and (2) the peculiar position in the right auricle of the orifice of the great cardiac vein. 

 The notching of the right auricular appendix cannot be regarded as a universal distinc- 

 tion, but when it is present it is a feature of great prominence. It is very clearly figured 



(ZOOL. CHALL. EXP. — PART XVI. 1882.) Q 20 



