704 MR. F, G. PARSONS ON THE [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. 
The Vascular System. 
The Heart in Petrogale 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 column 
carnez of the second and third kinds; these are so broad and 
numerous that the wall presents quite a smooth appearance, the 
intervals between the columne appearing as small rounded pits. 
There are no musculi papillares or chord tendineew attached to 
this wall, nor is there any moderator band. The right auriculo- 
ventricular valve las four cusps, one of which is much larger than 
the rest and les against the septal wall, to which its free edge is 
connected by a large number of short chorde tendinez without 
any musculi papillares. There are only two (Owen says three) 
musculi papillares in the right ventricle; they are attached to the 
septal wall, the larger about halfway down, the smaller dorsally 
and above. ach of these sends chord tendinee 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 chordx tendinee which 
spring from several large musculi papillares 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-thirds. 
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 Petrogale 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 poiuts cut, 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 annulus ovalis. The left auricle has 
musculi pectinati only in the appendage, which is large and forms 
a great part of the cavity. Owen describes it as being notched, 
but this I failed to make out. The two pulmonary veins open 
close together into the dorsal wall. 
1 © Anatomy of Vertebrates,’ vol. iii. p. 517. 
