THE SKELETON 



85 



finally, on the assumption of the upright gait, it has changed 

 back into an ambulatory appendage. 



This ultimate modification has been accompanied by the greater 

 development of the tarsus, and 

 by the concomitant degeneration 

 and decreasing mobility of the 

 phalanges ; and, correlatively, the 

 foot has acquired a disposition at 

 a wider angle to the fore-leg, and 

 has become arched in adaptation 

 to its supporting function. 



These repeated changes of 

 function may well have resulted 

 in great structural changes, 

 which we may now consider in 

 some detail. 



First, comparing the skeleton 

 of the human foot with that of 

 the Anthropoid Apes, we find the 

 former distinguished by the fol- 

 lowing three points (cf. Figs. 60 

 and 62): 



(1) Stronger development of 

 the great toe. 1 



(2) Greater development of 

 the tarsal elements. 



(3) Displacement of the great 



toe into a position of parallelism Fl - ^.-SKELETON OF THE LEFT PES 



x OF A CHIMPANZEE, DORSAL ASPECT. 



With the Other toes. ec>> ec to-cuneiform ; en., ento-cuneiform ; 



If the foot of a second 

 month's human foetus be ex- 

 amined, with special regard to 

 the last point, it will be seen (Fig. 63, B) that the position of 

 the great toe almost entirely agrees with that of the thumb 

 (63, A). When the limbs are laid against the trunk, both point 

 towards the head in the position of abduction. 



Whereas this is the normal lifelong position of the great toe 

 of the Apes, and of the human thumb (cf. Figs. 60 and 61) in 

 the human foot it is merely transitional, and is abandoned 



1 We have herein a noteworthy contrast to most of those lower Mammals in 

 which the great toe is reduced, or has altogether disappeared. A claw may in the 

 former case be found at its distal end (e.g. in the Dog), but even that may disappear. 



ms., meso-cuneiform ; cb., cuboid ; m\, 

 navicular ; as., astragalus ; cl. t cal- 

 caneum ; I-V, digits. 



