OF THE MARSUPIALIA. 405 
Koala, is almost plane from side to side. I find distinct but small bony patelle in the 
Macropus Bennettit. 
In the knee-joint, besides the two crucial ligaments continued from the posterior 
angles or cresses of the semilunar cartilages,—one to the outer side of the inner con- 
dyle, the other to the interspace of the condyles,—there is a strong ligament which 
passes from the anterior part of the tibial protuberance backwards, to the inner side of 
the fibular condyle ; and a second continued from the same point, along the outer mar- 
gin of the outer semilunar cartilage, to the head of the tibia. 
The tibia presents the usual disposition of the articular surface for the condyles of 
the femur ; but in some genera, as the Wombat and Koala, the outer articular surface is 
continuous with that for the head of the fibula. a Kangaroos and Potoroos the an- 
terior part of the head is much produced, and in*the young animal its ossification com- 
mences by a centre distinct from the ordinary proximal epiphysis of the bone. A strong 
ridge is continued down from this protuberance for about one-sixth the length of the 
tibia. In the Koala a strong tuberosity projects from the anterior part of the tibia at 
the junction of the upper with the middle third. In this species and in the Wombat, as 
also in the Opossums, Dasyures, Phalangers and Petaurists, the shaft of the tibia is some- 
what compressed and twisted ; but in the Kangaroos, Potoroos and Perameles, the tibia 
is prismatic above and subcylindrical below. The internal malleolus is very slightly 
produced in any Marsupial, but most so in the Wombat. 
The fibula is complete, and forms the external malleolus in all the Marsupials. In 
one species of Hypsiprymnus, and in one species of Perameles (Per. lagotis), it is firmly 
united to the lower part of the tibia, though the line of separation be manifest exter- 
nally. In a second species of each of the above genera it is in close contact with the 
corresponding part of the tibia, but can be easily separated from that bone. 
In the Great Kangaroo the fibula is also a distinct bone throughout, but it is remark- 
ably thinned and concave at its lower half, so as to be adapted to the convexity of the 
tibia, with which it is in close contact and attachment. In each of those genera, there- 
fore, in which locomotion is principally performed by the hinder extremities, we per- 
ceive that their osseous structure is so modified as to ensure a due degree of fixity and 
strength ; while in the other marsupial genera, as Phascolarctos, Phascolomys, Phalan- 
gista, Petaurus, Didelphys and Dasyurus, the tibia and fibula are so loosely connected 
together, and with the tarsus, that the foot enjoys a movement of rotation analogous 
to the pronation and supination of the hand; and in the Petaurists, Phalangers, Opos- 
sums, and Koala, the inner toe is so placed and organized as to perform the office of 
an opposable thumb, whence these Marsupials have been termed Pedimana, or foot- 
handed. It is to this prehensile power that the modifications of the fibula chietly 
relate. Inthe Wombat, Koala, Petaurists and Phalangers, it expands to nearly an equal 
size with the tibia at the distal extremity, and takes a large share in the formation of 
the tarsal joint; but the articular surface is slightly convex, while that of the tibia is 
