408 THE ANATOMY OF VERTEBRATED ANIMALS. 



metatarsal bone of the digit ; in the Gorilla, they are about 

 equal in length to the metatarsal. The calcaneal process is 

 longest, strongest, and broadest, in the Gorilla. In the astrag- 

 alus the articular surface for the tibia is broadest in the Goril- 

 la ; but, in this Ape, as in the others, it is inclined a little in- 

 ward when the foot is in its natural position ; and the surface 

 for the external malleolus is oblique, and looks upward as well 

 as outward. 



It is a mistake, however, to suppose that the disposition 

 of these surfaces has any thing to do with the more or less 

 marked tendency of the plantar surface to turn inward, and 

 of the outer edge of the pes to be directed downward, which 

 is observable in all the Anthropomorpha. This tendency is 

 the result of the free articulation between the scaphoid and 

 the cuboid, on the one hand, and the astragalus and the calca- 

 neum on the other ; the consequence of which is, that the dis- 

 tal portion of the pes, with the first-mentioned bone, being 

 pulled by the tibialis anticus, easily rotates round its own 

 axis, upon the surface presented by the astragalus and calca- 

 neum. This ready inversion of the sole must as much facili- 

 tate climbing, as it must interfere with the steadiness of the 

 foot in walking. 



The distal surface of the ento-cuneiform is much inclined 

 inward in all the Anthropomorpha^ and is convex from side to 

 side, or subcylindrical. The metatarsal bone of the hallux pre- 

 sents a corresponding articular concavity to this surface, and 

 has a great range of motion in adduction and abduction. Thfj 

 inward inclination of the articular facet of the ento-cuneiform, 

 and its consequent separation from the facet upon the mcso- 

 cuneiform for the second digit, is greatest in the Orang, in 

 which the hallux is habitually directed at right angles to the 

 long axis of the foot. The distal phalanx of the hallux is not 

 unfrequently absent in the Orang. 



All the Anthropomorpha possess certain muscles which 

 are not usually found in Man, though they may occur as vari- 

 eties in the human subject. These are the levator claviculce, 

 the dorso-epitrochlearis, the scansorius* and the abductor 

 ossis metacarpi quinti digiti. They are also devoid of two 

 muscles which are usually present in Man — the extensor primi 

 internodii pollicis\ and ihe peronceus tertitts. The former of 



* Not actually described in the Gorilla, and absent in some Cbimpanzees. 



t The former muscle is said to be present by several anatomists in tha 

 Chimpanzee and other Apes ; but what they have taken for it is the metacar- 

 pal division of the extemw oesis metacarpi. 



