VESTIGIAL STRUCTURES. 



99 



As the fibula in nearly all mammals is thin, slender, 

 and almost vestigial, we have yet to inquire how it is 

 that Pott's fracture is peculiar to human beings. A 

 comparison of the human malleoli with those of mammals 

 shows that man differs from them in that the external or 

 fibular malleolus descends much lower than the tibial 

 malleolus : even in those mammals which so closely ap- 

 proach man in anatomical characters as the gorilla, chim- 

 panzee,orang,gibbon, and macaque, the malleoli are on the 

 same level. In the accompanying sketches, fig. 50, the 



FIG. 50. A, the malleoli of the Chimpanzee ; 

 M, the malleoli of Man. 



malleoli of man and a chimpanzee are introduced for 

 comparison. 



In 1886 Gegenbaur published the highly interesting 

 observation that, in the human embryo at the fifth month 

 of intra-uterine life, the tibial is more prominent than 

 the fibular malleolus ; at the seventh month they are 

 equal ; from this date onward the fibular exceeds in 

 length the tibial malleolus. Thus at the fifth month the 

 human malleoli present a condition common to the 

 majority of mammals ; at the seventh month they corre- 



