330 THE THIGH AND LEG. [CHAP. 



process called internal malleolus, which is applied to the 

 side of the astragalus, giving additional strength to the 

 articulation called "ankle-joint." 



The fibula has a slender and generally compressed shaft, 

 and is somewhat expanded at each extremity. Its upper 

 end usually takes no part in the knee-joint, being con- 

 nected, by a separate synovial joint, with the tibia just 

 below that articulation. The lower end, however, forms the 

 outer side of the ankle-joint, under the name of external 

 malleolus. 



In many Mammals the fibula is in a more or less rudi- 

 mentary condition, and it often ankyloses with the tibia at 

 one or both ends. 



As a general rule each of these bones has a principal 

 centre of ossification for the shaft, and an epiphysis at 

 either end. 



In the neighbourhood of the knee-joint, certain sesamoid 

 bones are often found in connection with the tendons which 

 pass over the various bony prominences. 



The largest and most constant is the patella, placed on 

 the anterior surface of the joint, in the conjoined tendon 

 of the four great extensor muscles of the leg, and having 

 a smooth articular facet, which plays upon the narrow 

 anterior part of the inferior articular surface of the femur, 

 and forms part of the wall of the cavity of the knee joint. 

 This bone varies considerably in form, being in some cases 

 broad, flattened, or lozenge-shaped, and in others, laterally 

 compressed or oval. It is found in an ossified con- 

 dition in all Mammals, with the exception of a few of the 

 Marsupialia. 



There are also very frequently smaller ossicles, one 

 or two in number, situated behind the femoral condyles, 

 called fabcllai ; and occasionally there is a wedge-shaped 



