THE SKELETON 35 



The patella is formed within the tendon of the quadriceps 

 femoris m. (42) (patellar ligament) and is, therefore, a sesa- 

 moid bone; but most anatomists enumerate it with the bones 

 of the human skeleton. 



The tibia and fibula are fused together and thus form the 

 tibiofibula (Fig. 16). The proximal end of the tibia is tri- 

 angular in cross section with the articulating surface greatly 

 expanded. The apex of the triangle is directed craniad and 

 forms the crest of the tibia. The distal end of the tibia articu- 

 lates with the calcaneum and astragalus and presents two 

 eminences; the medial (internal) malleolus and the lateral 

 (external) malleolus. The lateral malleolus has a groove on 

 the caudal side, the peroneal notch, through which the tendons 

 of the peroneal muscles (50) pass. 



The tarsus (Fig. 17) has only six bones, which indicates a 

 marked advance from the generaUzed vertebrate type. The 

 reduction in number and increase in relative size of other 

 tarsals, as compared with man, are correlated with development 

 of leaping. 



There are four metatarsals; the first is absent, as is also 

 the hallux. Each of the four digits has three phalanges. 



