From the Unconscious to the Conscious 



progressive reduction in the number of the digits 

 in the latter. The horse, for example, by its adaptation 

 to speed, has but one digit, the median, much hyper- 

 trophied and terminated by a thick layer of horn, and two 

 rudimentary metacarpals accessible only by dissection; 

 but the reduction in the number and size of the lateral 

 digits is seen in the evolutionary series of its ancestors. 



The formation of the articulations of the foot and 

 hand of mammals is equally typical. He observes 

 as follows: 



The articulation of the foot, which is very strong, 

 presents two processes of the astragalus, the leading 

 bone of the foot, which project into two corresponding 

 sockets of the tibia, and a process of this latter fitting 

 into a socket of the astragalus. This structure does 

 not (as yet) exist either in the inferior vertebrates, 

 such as reptiles, or in the ancestral mammals of each 

 of the great living branches; it has been formed 

 little by little, by reason of a certain mode of move- 

 ment and a certain attitude of the animal. 



The external walls of these bones being formed 

 of stronger material than their central parts, the 

 sequence of development would seem to be as 

 follows: the astragalus is narrower than the tibia 

 which rests upon it, therefore the peripheral parts 

 of the former bone, being in contact not with equally 

 resisting parts of the latter but with portions relatively 

 softer, these, under this pressure, have suffered a 

 certain absorption of their substance, and two 

 depressions corresponding to the two edges of the 

 astragalus have been formed. This is precisely what 

 would be produced in more or less plastic, inert 

 substances under continuous pressure. 



The central depression in the upper edge of the 

 astragalus arises from a similar cause. Here the 

 inferior extremity of the tibia, having a relatively 



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