THE SKELETON 83 



In the lower Mammals both tibia and fibula articulate with 

 the femur, and contribute to the formation of the knee-joint. 

 In Man, under advancing phylogenetic development, the weight 

 of the body has come to rest on the tibia alone, and the proximal 

 end of the fibula has become disconnected from the femur, 1 

 and has shortened and shifted downwards along the postero- 

 external surface of the tibia. 



The human fibula- is now an appendage of the tibia, and the 

 fact that its degeneration has not gone farther 2 is accounted 

 for partly by its important connection with the heads of certain 

 muscles of the leg (especially the peronei), and by the part which 

 it plays in the formation of the ankle (external malleolus). 



The external condyle of the tibia varies very much in different 

 races. In the lower races it is much more convex than in the 

 higher, and this is probably also the case in the oldest prehistoric 

 men. This convexity is evidently connected with the frequent 

 strong flexure of the knee-joint, such as occurs in squatting. 



On the inner border of the distal extremity of the tibia 

 | (malleolus internus) there is, in the lower races, a special facet 

 ' which articulates with the neck of the astragalus ; and the presence 

 I of this may be also connected with the strong " dorsal flexion " 

 consequent on the squatting posture. The astragalo-tibial articula- 

 tion thus formed rarely occurs in the higher races ; but parallel 

 modifications of both the upper and lower ends of the tibia occur 

 in the Anthropoids and among the lower Apes (Arthur 

 Thomson). 



Until approximately the seventh month of fcetal life, the 

 tibial malleolus is larger than the fibular, projecting downwards 

 farther than the latter. In the seventh month the two appear 

 about equal, and then the fibular malleolus begins to take the lead. 

 These phases of development are accompanied by corresponding 

 modifications of the astragalus (Gegenbaur). 



That the earlier condition of these bones is the inherited one 

 seems probable from comparison of those of the Lemuroidea, Apes, 

 and lower human races. Fig. 59 illustrates the manner in 

 which the external or fibular malleolus (c/.) gradually, in adaptation 



1 [The human fibula has been stated by Leboucq, Bernays, and others, to be 

 during early development in contact with the femur, from which it would appear that 

 the loss of connection between the two takes place ontogenetically. Griinbaum, 

 examining the parts with extreme care, has lately shown (Jour. Anal, and Phys., 

 vol. xxvi. p. xx.) that this is not the case from the period of primary differentia- 

 tion of the parts in cartilage onwards.] 



2 In many lower Mammals it has still further degenerated. 



