152 THE VOYAGE OF H.M.S. CHALLENGER. 



The right auriculo-ventricular opening is guarded by a valve formed of five triangular 

 membranous cusps. Three of these be anteriorly against the anterior wall ; one lies to 

 the right in relation to the sharp margin of the heart ; whilst the fifth is placed 

 posteriorly against the septum. United at their bases, the five segments constitute 

 an annular membrane by which they are attached around the opening. The three 

 anterior cusps are very small and of equal size ; the posterior segment is very large ; 

 whilst the right segment is intermediate in size. 



The orifice of the pulmonary artery is guarded by the usual three semi-lunar valves. 



Left auricle. — The appendix of the left auricle is filled by a very beautiful arrange- 

 ment of musculi pectinati. These intersect one another, and pass between the walls so 

 closely that the cavity is broken up into a sponge-like texture. There are no muscub pec- 

 tinati on the walls of the atrium. On the posterior wall there are three venous openings. 



Left ventricle. — The cavity of the left ventricle is very narrow and of a conical shape. 

 The fleshy columns are very strongly marked, some, indeed, stretching as thick prominent 

 ridges from the ariculo-ventricular orifice to the apex. The musculi papillares are two 

 in number, and very powerful. The auriculo-ventricular valve is bicuspid, and the 

 segments are placed obliquely as in Man. The orifice of the aorta is provided with the 

 usual three semilunar segments. 



Turning now to the Dasyurus viverrinus we find that the right auricle of the heart is 

 in every respect the same as in the Thylacine. There is no bifurcation of its appendix, 

 and its interior presents the same appearance. 



In the right ventricle what strikes one most is the extreme smoothness of its walls. 

 There is hardly a trace of columna3 eameae except where the septum joins the anterior 

 wall ; here we notice a series of " moderator bands " passing from the septum to the 

 anterior wall of the ventricle. The musculi papillares are three in number, and they all 

 spring from the septum. The right auriculo-ventricular valve is peculiar. In front and 

 at the sides of the orifice there is simply a membranous curtain of uniform length 

 hanging down into the cavity, and to this all the chordae tendineee from the three 

 muscub papillares are attached. Behind, there is a broad separate segment which is 

 bound directly to the septum by chordae tendineae. 



The left side of the heart in the Dasyure is the same as in Thylacine. 



In Cuscus the heart has the same elongated narrow appearance as in Thylacinus. 

 The right auricular appendage, however, presents a deep crescentic notch on its inner free 

 margin into which is received the first part of the aortic arch. So deep is this notch 

 that the aorta is almost completely surrounded by the appendix, and the posterior or 

 upper cornu appears in the internal between the pulmonary artery and the aorta. The 

 left auricular appendage shows no notching, and stretches inwards for a considerable dis- 

 tance in front of the conus arteriosus and the pulmonary artery in the form of a narrow 

 tongue-like process. 



