488 BONES AND MUSCLES OF THE FOOT. 
the side of the foot; and the absence of a projecting heel 
causes them to he very deficient in the power of keeping the 
leg upright upon it. For it is to this projection that the 
strong muscles of the calf of the leg are fixed, by which the 
heel is drawn upwards or the leg drawn back upon it. Other 
muscles at the side and back of the leg, the direction of whose 
tendons is changed by a sort of pulley at the ankle-joint, 
aided by the muscles of the foot itself, serve to bend the toes, 
—an action which gives great assistance in walking, running, 
leaping, &c. And the toes are -straightened by an extensor 
muscle, which lies on the front of the leg, and of which 
the tendon runs under an annular ligament that encircles 
the ankle, and is then divided and spread - out to the 
toes, over the upper surface of the foot. The great toe is 
a very important instrument in the act of walking, since 
much of the spring forwards is given by the -bending of 
its phalanges; and it is provided with two flexor muscles 
of its own. 
649. On the internal side of the foot, the bones of the 
tarsus and metatarsus form a kind of vault or arch, which 
serves to lodge and protect the : vessels and nerves that 
descend from the leg towards the toes. This arch further 
serves the important purpose of deadening the shock that 
would otherwise be experienced every time that the foot is 
put to the ground; for, by the elasticity of the ligaments 
which hold together the bones that compose it, a sort of 
spring is formed, which yields for a moment to the shock, 
and then recovers itself. We feel the difference which this 
makes, when we jump from a height upon our heels ; the jar 
is then propagated directly upwards from the heel to the leg, 
thence to the thigh, and thence to the spinal column, and if 
it were not from the peculiar manner in which this is con¬ 
structed (§ 631), a severe shock of this kind might produce 
fatal effects by concussion (or shaking) of the brain. In 
animals which walk upon four extremities, the difference of 
direction in which the legs are connected with the spine 
prevents a jar from being propagated along the latter to a 
similar degree. But in those which are destined to obtain 
their food by sudden and extensive leaps, such as the animals 
of the Cat tribe (the Lion, Tiger, &c.), we find an arrange¬ 
ment of the bones of the foot, well adapted to diminish the 
