ANATOMICAL STRUCTURE OF THE WOMBAT. 179 



" There is no patella; but the tendon of the extensor 

 muscles of the leg, where that bone is usually situate, is 

 much thickened. 



" The fibula is proportionably larger than in most ani- 

 mals. At the upper extremity it is broad, and has two dis- 

 tinct articulating surfaces: the anterior of which is articu- 

 lated to the tibia, and the posterior to a small borie of a py- 

 ramidal shape, which is connected to the tendon of the ex- 

 ternal head of the gastrocnemius muscle like a sesamoid 

 bone. The lower extremity of the fibula is large, and forms 

 about half of the articulating surface for receiving the tar- 

 sus at the ankle. An interarticular cartilage is here inter- 

 posed between the tibia and the fibula, and another between 

 the fibula and the tarsus. 



" The fibula has a slight degree of motion on the tibia at 

 its upper end, and a half rotatory motion on it at its lower 

 end. Between the two bones is a strong muscle, which 

 passes from one to the other throughout their whole length. 

 The fibres have their origin from the inner edge of the fibula, 

 and pass obliquely inward and downward to be inserted into 

 the opposite surface of the tibia. When this muscle con- 

 tracts, it pulls the fibula forwards, and produces a degree of 

 rotation on the tibia, which turns the toes inwards. The an- 

 terior surface of the muscle is covered by a thin fascia or in- 

 terosseous ligament, and there is another fascia less complete 

 on its posterior surface. The muscle of the legs,correspofiding 

 to the biceps flexor of the human subject, is inserted into 

 the posterior part of the fibula, and is an antagonist to the 

 muscle just described. Its action brings the toes back to d 

 straight line, but does not turn them Outwards." 



This mechanism is met with in two animals, whose mode This structure 



of life is very different, the one living on trees, the other comm ° n to - 

 , i,i, • , , , • . . , two animals of 



not; but as they both burrow in the ground diinngthe night, different ha- 

 lts use appears to be for throwing back the earth while the bits * 

 animal is burrowing* There is nothing at all similar to it 

 in the hind legs of the mole, or other burrowing animals. 



The internal structure of the stomach of the wombat re- Stomach,, 

 srembles very closely that of the beaver. This is so differ- 

 ent from that of the kangaroo, and all the other animals of the 

 oposBum tribe, that it forms a very extraordinary peculiarity. 



N2 IVa 



