THE PLANTAR ARCH 197 



a nature) and the long flexors of his four outer toes, the special 

 long flexor of the great toe, which in his case does not of course act 

 in the axis of the other metatarsal bones. He is lacking here in 

 the special detached portion of the flexor accessorius, which eventually 

 becomes of use in maintaining the arch, between the heel-bone 

 and the tendons of certain digits. He has, in a measure, the 

 oblique adductor muscle of the great toe and the transverse adductor 

 muscle, more for future use perhaps than of much present value. 

 Like all apes and monkeys he has a peroneus longus with its tendon 

 passing across the sole from the outer border to the base of the 

 great toe and a peroneus brevis, both of them for everting the foot 

 and supinating it. But here again he is lacking, for he has no 

 little peroneus tertius, which Professor Keith speaks of as a muscle 

 " peculiar to man " and " a special evertor of the foot " — a muscle 

 passing from the tendons of the extensors of the toes and inserted 

 into the little toe. He has also the tibialis anticus and tibialis 

 posticus, the latter which flexes the ankle on the leg, and the former 

 which also flexes it and everts the foot ; he has also the special 

 extensors of the toes. 



This enumeration of the bony, ligamentous, and muscular 

 possessions of gorilla C. is enough to show that, though he has 

 little of new tools to make, he has to modify greatly those he 

 has learnt to use so well, so that one can almost hear him echo the 

 words of David to Saul as to his new armour. 



The problem of an arch remains to be solved by eversion 

 instead of inversion of the foot, growth in all directions of the heel- 

 bone, and the enlargement and straightening of the great toe, 

 and the " setting " of the foot in a certain degree of pronation and 

 over-extension. 



Description of the Arch. 



The plantar arch is double, but the longitudinal one must 

 be chiefly considered here. It lies under the concave roof of the 

 tarsal bones, seven in number, and the metatarsal bones, and rests 

 in a well -formed foot in front on the heads of the latter, and behind 

 on the inferior surface of the heel-bone. The astragalus alone of 

 these bones in contact with those of the leg, acts like a washer to 

 the ankle joint, and has no muscles attached to it. Three more 

 of the tarsal bones need reference : these are the three wedge-shaped 

 bones which have their bases on the dorsal and their apices directed 

 towards the plantar surface. With such a set of bony tools as 

 this, all the requisites for an arch are at hand. Let the half -tree, 

 half-ground walker become a complete ground -walker, and in 

 the first place the manifest increase of the action of the flexors of 



