The muscles compose the flesh or chief part of the bulk of a limb. The “calf” is almost entirely made up of the fibres of the “calf-muscle.” But at the ankle there are no muscles. As they descend the leg, all the _muscular_ fibres disappear, and there are only _tendons_. These, though much thinner than the muscles, are very strong; and they are the cords or ropes by which the muscles pull upon distant parts. As they pass over the ankle they are strapped down close to the bones by means of stout sinewy cross-bands, which prevent their starting from their places when the muscular portions pull at them. Two especial advantages result from this arrangement. _First_, the lower part of the leg and the ankle are reduced in size. Thereby the resistance to the passage of the limb through the air is lessened; and when it is upon the ground, the leg is less in the way of the other foot which is swinging, to and fro, beside it. An elegance of shape is also thereby imparted. The “pretty ankle” owes much of its charm to the mode in which the tendons are disposed. How comparatively thick and clumsy would the ankle be if the tendons of the toes took the straight course represented by the line _a_ in the drawing, instead of being bound down, as they are, to the curve of the ankle! [Illustration: Fig. 15.] _Secondly_, the obliquity with which the tendons run to their insertions is increased by this arrangement; and the velocity of the movements to which they minister is increased also. True, a loss of strength is involved in such a disposition, but the gain in velocity is of more importance. If (to refer again to the diagram, fig. 15) the tendon ran in a straight course from the front of the leg to the great toe, the angle at which it joined the toe would enable it to act with more strength; but the movements connected with it could not be so quick as they now are. We find in the construction of the human frame many instances in which strength is sacrificed to rapidity of movement in this and other ways. Scarcely any conceivable amount of strength, for instance, would be an adequate compensation for a loss of that celerity of movement of the hand which enables us to strike a blow and drive a nail. No wonder, therefore, that strength is here sacrificed to obtain celerity. And the same principle holds good for other parts. The length and direction of the heel affords a good illustration of the principle of which I am speaking. When the heel-bone runs out to a considerable distance, and nearly straight, behind the ankle, as it does in some of the lower animals and in the inferior races of mankind, it presents a better leverage to the calf-muscle, which is, then, enabled to raise the ankle with a less amount of effort; but there is proportionately less velocity. Accordingly, in the more perfectly formed foot, such as we find it in the higher races of mankind, the heel-bone, instead of running out backwards, descends very obliquely, almost vertically.