XVIII.] 



MARSUPIALIA. 



337 



of the articular surface of the astragalus, as a pivot into 

 a socket. 



In none of the MARSUPIALIA is a third trochanter pre- 

 sent on the femur. The fibula is always well developed, 

 and its proximal extremity is often produced into a well- 

 marked process, to the top of which a sesamoid bone is not 



FIG. T2i. Anterior aspect of bones of right leg of Ornithorhynchiis anatimis, 4 

 f femur ; / tibia ; /' fibula ; p patella. 



unfrequently attached ; but, on the other hand, the patella, 

 except in the PeramelidcR^ is unossified or quite rudimentary. 

 In Ch&ropus and Hypsiprymnus the distal end of the fibula 

 is united with the tibia. In the climbing Australian 

 Phalangers and Koalas, which have broad hind feet, with an 

 opposable hallux, there is a greater freedom of movement 

 between the fibula and tibia than in other Mammals, 



z 



