110 THE STRUCTURE OF MAN 



begun to degenerate from the time that the plantar fascia became 

 secondarily attached to the calcaneum, and helped in the forma- 

 tion of the arch of the foot, as the latter became transformed 

 into a supporting organ. 



But why are the palmaris and plantaris of Anthropoids, 

 in which such transformations do not take place, also in a 

 degenerate condition? It does not appear difficult to answer 

 this question if we consider that these muscles originally 

 extended, as do their homologues in the lower Mammals, 1 

 through the mediation of the palmar or plantar fascia to the 

 phalanges, and acted as common flexors of the fingers and toes. 

 If so, in the course of time to confine our attention to the 

 hand as the flexores digitorum communis superficialis and pro- 

 fundus became more extensively and more subtly differentiated 

 from the primitive " pronato-flexor mass " (Humphry), the fibrous 

 terminal expansions of the palmaris withdrew more and more 

 from the fingers, and found points of attachment in the palm of 

 the hand and in the ligamentum carpi transversum. Thus 

 would the finger flexor appear to have become a hand flexor. 

 As such, however, it could not, on account of its attachments, 

 develop the same strength as the proper hand flexors, 2 which are 

 directly attached to the skeleton, and which, as we see where 

 the palmaris is wanting, are competent alone to bend the hand. 

 The palmaris becoming thus superfluous, is variable and occasion- 

 ally absent. 



A further consequence of the transformation of the hind-limb 

 into a supporting and ambulatory organ, is that some of the 

 flexor muscles which originally ran down without interruption to 

 the sole of the foot have become interrupted at the protuberantia 

 calcanei by the dorsal flexion entailed. Another muscle of this 

 flexor series, e.g. the short flexor, which corresponds with the 

 flexor digitorum communis superficialis of the hand, has shifted 

 its point of origin farther and farther down, till at last, on the 

 acquisition of the upright gait, it has reached the calcaneal 

 tuberosity. In doing so this muscle has become more and more 

 closely connected with the plantar fascia ; and at present it 

 shows in many ways, e.g. in the variation of its terminal tendons 



1 It is said that in Negroes the palmaris is still not infrequently inserted into 

 the metacarpals. 



2 That it is still functional in the hand is shown by its occurrence, which must 

 still be considered normal. It is absent on one or both sides in about one in every 

 ten bodies. 



