The inner aspect of the foot, showing the arched construction of the whole foot—_a_, head of metatarsal bone of great toe,—_b_, calcaneum,—_c_, astragalus. ] The forward part of the _calcaneum_, or heel-bone, at its lower surface, is somewhat higher than the back part, and has under it a thicker cushion of flesh. When the bare foot treads upon the surface, or when there is no heel upon the shoe-sole, this point—letter _e_ in the diagram—is as well supported as any other, and, being so, enables all the other bones to keep their proper places, but when there is a heel on the sole of the shoe, it _is not long enough—does not extend under far enough_—to support this _forward part_ of the heel-bone. The sole, forward of the heel, is not usually stiff enough to support it, and therefore it falls downward as much as the leather will give way; the heel-piece being often half an inch too short, and sometimes more than that. Then, if the sole is light, so as to give way easily, there is nothing to prevent this part of the bone from settling down to the extent of a quarter of an inch, or even more. While the back part is supported, the front is turning directly downward. This allows the astragalus and the whole arch to sink down to the same extent, and, in time, all parts of the foot will adapt themselves to their changed condition, and the flat shank become a permanent thing. If any person will examine a slipper worn with a heel, or a _boot_ having an ordinary sole, it will be seen that just in front of the heel the sole is depressed, or bent downward, from one-eighth to three-eighths of an inch. This is almost invariable, except when a very long heel, or a stiff shank in the sole, preserves the natural position of the _calcaneum_ or bone of which the heel is formed. The amount of this depression shows how much the arch has sunk, and how much higher it would be if properly supported. It indicates very plainly the occasion and origin of a large proportion of the flat and splay feet that may be so frequently observed. This inefficiency of the common short heel to properly support the arch was first discovered by Dr. J. C. Plumer, of Boston, to whom is due the credit of showing the bad effects just noticed as the result of its being worn. His style of boot and last will be discussed further on. It has been stated that as the foot flattens, it also lengthens. It has been estimated that some flat feet are as much as two sizes, or two-thirds of an inch, longer than the same feet would be if well arched; an item worth noticing by those who are fastidious upon this point.