ioo EVOLUTION AND DISEASE. 



spond to the simian type, and subsequently assume the 

 relation normal only in man. This extra length of the 

 fibular malleolus gives great firmness to the ankle-joint, 

 and has probably been acquired concurrently with the 

 assumption of the erect posture. It is to this extra 

 length of the outer malleolus, associated with the slender- 

 ness of the fibula, that the frequency of Pott's fracture 

 may be largely attributed ; the long fibular malleolus 

 affording good leverage when the foot is violently and 

 suddenly twisted laterally, the force applied to the long 

 distal end causes the fibula to snap at some point in its 

 lower fourth. 



This inquiry, when pushed further, leads to other 

 points of interest. The foot of an orang, instead of 

 forming a right angle with the leg, as in man, has its 

 inner border drawn upwards in such a manner that the 

 sole of the foot looks inwards, and the back, or dorsum, 

 of the foot looks outwards. This position of the foot is 

 associated with a peculiar disposition of the articular 

 surfaces of the astragalus, or ankle-bone. In the human 

 embryo, up to the seventh month, the foot has a similar 

 position, and the articular surfaces are disposed as in the 

 orang ; after the seventh month the foot gradually 

 passes into the position characteristic of the adult, but 

 not infrequently it retains the simian position and the 

 child is said to be club-footed, or, properly speaking, it 

 has talipes equino-varus. Messrs. Parker and Shattock 

 have clearly shown that the articular surfaces of the 

 astragalus in cases of congenital talipes equino-varus 

 retain the ape-like disposition, and it occurred to me 

 that if this is constant, the fibular malleolus in children 



