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 



Fin. ui. Anterior aspec* of loncs of right leg of Ornithorh^nckut nnatinut, * . 

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



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

 except in the Pframelidie, is unossified or quite rudimentary. 

 In Chatrofus and Ifyf>sif>rymnus 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, 



