406 - PROF. OWEN ON THE OSTEOLOGY 
slightly concave. The proximal extremity of the fibula is also much enlarged, but 
compressed, obliquely truncated, and giving off two tuberosities from its exterior sur- 
face ; to the superior of these a large sesamoid bone is articulated: I have observed the 
same sesamoid attached to the upper end of the fibula in a Dasyurus macrourus. Tem- 
minck figures it in the Didelphys ursina and Didelphys Philander. 
I find the following structure of the tarsus in the Wombat. The astragalus is con- 
nected, as usual, with the tibia, fibula, calcaneum and scaphoides. The upper articular 
surface for the tibia is, as usual, concavo-convex, the internal surface for the inner 
malleolus flattened, and at right angles with the preceding ; but the outer articular sur- 
face presents a triangular flattened form, and instead of being bent down parallel with 
the inner articular surface, slopes away at a very open angle from the upper surface, 
and receives the articular surface of the fibula so as to sustain its vertical pressure. 
A very small proportion of the outer part of the inferior surface of the astragalus rests 
upon the calcaneum ; a greater part of the superincumbent pressure is transmitted by a 
transversely-extended convex anterior surface to the scaphoid and cuboid bones. This 
form of the astragalus is also characteristic of the Koala, Petaurists, Dasyures, and the 
Pedimanous Marsupials. In the Kangaroos, Potoroos and Perameles, which have the 
pedes saltatorii, the fibular articular surface of the astragalus is bent down, as usual, at 
nearly right angles with the upper tibial surface. The calcanewm presents a ridge on 
the outer surface, which serves to sustain the pressure of the external malleolus, which 
is not articulated to the side of the astragalus. The internal surface, which joins the 
astragalus, is continuous with the anterior and slightly concave surface which articulates 
with the cuboides. The posterior part of the bone is compressed ; it projects backwards 
for nearly an inch, and is slightly bent downwards and inwards. This part is relatively 
shorter in the Koala, Phalangers, Opossums and Petaurists, but is as strongly developed 
in the Dasyures as in the Wombat. In the Dasyurus macrourus I observe a small sesamoid 
bone wedged in between the astragalus, tibia and fibula, at the back part of the ancle- 
joint. In the Petawrus Taguanoides there is a supplemental tarsal bone wedged in be- 
tween the naviculare and cuboides on the plantar surface. In the Wombat the scaphoid, 
cuboid, and three cuneiform bones have the ordinary uses and relative positions. 
The analogy of the carpal and tarsal bones is very clearly illustrated in this animal. 
The anchylosed naviculare and lunare of the hand correspond with the astragalus and 
naviculare of the foot, transferring the pressure of the focile majus upon the three inner- 
most bones of the second series. The long, backward projecting, pisiform bone of the 
wrist closely resembles the posterior process of the os calcis; the articular portion or 
body of the os calcis corresponds with the cuneiform bone of the carpus ; the large carpal 
unciform represents the tarsal cuboides, and performs the same function, supporting the 
two outer digits ; the three cuneiform bones of the tarsus are obviously analogous to the 
trapezium, trapezoides, and os magnum. The internal cuneiform bone is the largest of 
the three in the Wombat, although it supports the smallest of the toes: it is of course 
