704 MK. r. G.PAKSONS ON TUB [June 16, 



middle layer consists of three double-headed flexores breves, the 

 innermost serving for the two small inner toes. The deep layer 

 contains two abductor muscles, one to the fourth, the other to the 

 fifth toe. 



3'/te Vascular System. 



The Heart in Pttrogale agrees in most respects with Owen's 

 description of the organ in the Great Kangaroo'; I propose, 

 however, to describe it a little more in detail. On opening the 

 right ventricle the ventral wall is seen to be covered by columnae 

 carneas of the second and third kinds; these are so broad and 

 numerous that the wall presents quite a smooth appearance, the 

 intervals between the columnae appearing as small rounded pits. 

 There are no musculi papillares or chordse tendinete attached to 

 this wall, nor is there any moderator band. The right, auriculo- 

 ventricular valve has four cusps, one of which is much larger than 

 the rest and lies against the septal wall, to which its free edge is 

 connected by a large number of short chordse tendineae without 

 any musculi papillares. There are only two (Owen says three) 

 musculi papillares in the right veutricle; they are attached to the 

 septal wall, the larger about halfway down, the smaller dorsally 

 and above. Each of these sends chordce tendineae to two cusps, 

 and in this way the three anterior segments of the right auriculo- 

 ventricular valve are stayed. 



In the left ventricle the auriculo-ventricular or mitral valve has 

 only two cusps, one of which is close to the aortic opening, the 

 other away from it. There are numerous chordab tendineae which 

 spring from several large musculi pajiillares arranged in two 

 groups. The aortic and pulmonary valves have the normal human 

 arrangement, the corpora Arantii being well marked. The right 

 auricle is elongated transversely, at its right extremity is the 

 opening of the posterior vena cava; in the dorsal wall close to this 

 and a little to the left is the opening of the left anterior vena cava. 

 The right anterior vena cava opens on the upper part of the dorsal 

 wall about the junction of the left third with the right two-third.". 

 At the left extremity of the auricle are the openings of two 

 appendages, one of which projects ventral to the aorta, the other 

 dorsal. Owen describes the right auricular appendage as being 

 notched, but in Petrocjale the notching is so deep that there are 

 two distinct appendages. There are many and well-marked 

 musculi pectinati in the right auricle, which are best developed on 

 the ventral wall. The right auricle, as Owen points out, is 

 remarkable for the absence of all traces of foetal structures; there 

 are no signs of the Eustachian or Thebesian valves, nor is there any 

 indication of the fossa or annul us ovalis. The left auricle has 

 musculi pectinati only in the appendage, which is large and forms 

 a great part of the cjvvity. Owen describes it as being notched, 

 but this I failed to make out. The two pulmonaiy veins open 

 close together into the dorsal wall. 



' 'Anatomy of Vertebrates,' vol. iii. p. 517. 



