416 'rilE ANATOMY OF TERTEBIIATED ANIMALS. 



■sole is flat upon the ground ; and the lateral facets are more 

 nearly at right angles to this surface than in any Ape. The 

 inner and outer malleoli are stronger and more downwardly 

 produced. The calcaneal process is thick, strong, enlarged at 

 its hinder end, and not incurved inferiorly, but produced into 

 two tuberosities on which the heel rests. The form and dis- 

 position of the astragalar, navicular, and calcaneo-cuboid 

 articulations are such that the distal moiety of the tarsus is 

 capable of only a slight rotatory motion upon the proximal 

 portion. 



The distal articular surface of the ento-cuneiform bone is 

 very nearly flat, though it has a slight convexity from side to 

 side, and is irregularly concavo-convex, from above downward. 

 The comparatively slight mobility of the metatarsal bone of 

 the hallux arises partly from this circumstance, partly from 

 the fact that the proximal articular surfaces of the four outer 

 metatarsal bones are not perpendicular to the axis of those 

 bones, but are obliquely truncated, from the tibial side, back- 

 ward, to the fibular side. Hence the four outer metatarsal 

 bones, instead of diverging widely from the hallux as they 

 would do if their axis were perpendicular to the distal facets 

 of the meso- and ento-cuneiform and cuboid bones, take a direc- 

 tion more nearly parallel with the metatarsal of the hallux, 

 and the base of the second metatarsal, as it were, blocks the 

 latter, in adduction. The hallux thus loses most of its pre- 

 hensile functions ; but, in exchange, it plays an important 

 part in supporting the weight of the body, which, in the erect 

 position, falls on three parts of the pes ; namely, the heel, the 

 outer edge, and the integumentary pad which stretches be- 

 neath the metatarso-phalangeal articulations, from the hallux 

 to the fifth digit. 



In the infant, the sole naturally turns inward, and the 

 digits (especially the hallux) retain much of their mobility. 



The only muscles which exist in Man, but have not yet 

 been found in any Ape, are the extensor primi internodi ]}ol- 

 licis and the jyeronceus tertius. 



The only pecuharities in the origin of muscles v/hich ordi- 

 narily obtain in Man, and have not yet been found in the Apes, 

 are — the complete separation of the flexor poUicis longus ironi 

 xhe flexor digitorumperforans ; the presence of a tibial, as well 

 as of a fibular, origin of the soleus ; the origin of all four heads 

 oi the flexor hrev if: dif/itoruin p>edis from the calcaneum; the 

 origin of the fibula interosseus of the second digit of the pes 

 from the middle metatarsal, on the dorsal side of the tibial 



