Anatomi/ of Fibida. 361 



and distinct all through from the Tibia. Above we find the 

 outer tuberosity of the Tibia forming a smooth projecting rim 

 round which the head of the Fibula is allowed to play, resem- 

 bling somewhat the condition found in the Radius and Ulna 

 of the forearm. Tlie lower end is well developed and takes an 

 important part in the formation of the ankle-joint. There is 

 good muscular attachment of the Extensor muscles and 

 Peronei along the shaft of the Fibula. The disproportion be- 

 tween the two bones is not so marked as in man or the higher 

 mammjalia. 



" Opossum " ( Trichostirus). 



Here we have introduced as accessory to the use of the fore and 

 hind limbs that of the tail. There is a well-marked dispro- 

 portion between the Tibia and Fibula and both the upper and 

 lower ends are less defined than in Koala. Furthermore the 

 lower end partakes less in the formation of the ankle-joint. 



Wombat {Phascolomys). 



Here the disproportion in size between the bones of the leg 

 is very' pronounced — the atrophying Fibula and the enlarging 

 Tibia being well shown. The Interosseus muscle in contrast 

 to other parts of this marsupial's musculature shows marked 

 evidences of fibrous degeneration. The shaft is complete and 

 the upper end articulates with the Femur and Tibia and also 

 with the Sesamoid Bone. At the ankle-joint the chief articu- 

 lation is between the Tibia and the Astragalus and the Inner 

 Malleolus partakes in the articulation ; but the Outer Malleolus 

 though well developed does not. Below there is a well marked 

 Firbro-cartilage evidently to increase the surface of Fibula for 

 articuhition. 



Kangaroo {Macropus). 



Here the lower half of the Fibula as a distinct separate bone 

 has disappeared and the evidence of such is distinguished by 

 a groove. The upper half is distinct and separated from the 

 Tibia though fused to that bone at its lower end. The head 

 is poorly formed though it articulates with the Sesamoid bone 

 and the Outer Tuberosity of the Tibia. 



