The arch of the foot has to bear great weight and at great disadvantage; and there is very little in the _shape_ of the bones to maintain its integrity. Indeed, they all fall asunder when the other structures are removed, the key-bone dropping through of its own weight. And the same thing may be remarked throughout the skeleton. Wherever two or more bones move upon one another, their surfaces are so constructed that they do not hold together without some assistance from the soft parts. There are joints in the body which we call “hinge-joints,” and others which we call “ball-and-socket joints;” but in none of them is there such a holding and locking of one part in the other as you have in the hinge and the ball-and-socket of the mechanic. In every case the bones are held together, not by their own shape, but by ligaments and muscles. Consequently, any one of the bones may be dislocated from those next it without breakage; and when the muscles and ligaments are cut through, or have been destroyed by maceration, all the bones, between which any movement was possible during life, separate from one another. Not only is this so, but in no instance are the movements of joints _limited_ simply by the shape of the bones--that is to say, they are never brought to a stop by a part of one bone coming into contact with the edge of another. Such a contact would have caused a _sudden_ check; and this would have been attended with more or less jar and with some danger of chipping and breaking the articular edges. The range of movement of a joint is always regulated by the ligaments or the muscles, not, directly, by the bones; and the restraint thus imposed upon the movements is brought to bear, not suddenly, but _gradually_; somewhat like the effect of the “break” upon a railway-train; while the cartilages between the bones may be compared with the “buffers” between the carriages. It is chiefly by means of strong LIGAMENTS, or sinewy bands, passing from bone to bone, that the shape of the plantar arch is maintained and the movements of the bones upon one another are regulated and limited. These ligaments are numerous; but I will mention only two. [Illustration: Fig. 7.]