The _muscles_ of his leg and foot are the most important by far of his original equipment with which to set about making his arch: he could no more do this out of his present muscles than a Hebrew could make bricks without clay. It is these variable and plastic structures which are most readily adapted by use in a fresh direction or increased degree. He has the great flexors of the ankle and foot in his poorly-shaped calf (this feature might be adduced as a human character and studied in this manner if it were not of so elusive 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.