The spot over which this ligament extends is the weakest in the F., the astragalus being there unsupported by any bones; additional support is, however, afforded when it is most required by the tendon of a strong musclri, the posterior 'tibial, which passes from the back of the tibia (the chief bone of the leg) round the inner ankle, to be inserted into the lower part of the inner surface of the scaphoid bone. It not unfre quently happens that the astragalus, being either insufficiently supported, or from its being overweighted, descends slightly below its proper level, causing a lowering of the arch, and a flattening of the sole of the foot. The defect, when slight, is known as weak-ankle;" when more decided, it is termed "flat-foot;" and in extreme cases the bone may descend to such an extent as even to render the inner side of the F. convex, when it naturally should be concave.
The deformity of which we are speaking is of such great practical importance, that we shall add a few words about its most common causes.
There are two periods of life at which flat-foot is especially liable to occur: 1st, in infancy, if the child be put upon its feet before the bones and ligaments—especially the latter—are strong enough to bear its weight; and 2dly, about the age of 14—a period at which growth is very quick, and the body consequently attains a considerable and rapid augmentation of weight. If young persons of this age are obliged 'to be a great deal on their feet, and perhaps additionally to carry weights (as, for example, butchers' and bakers' boys, and young nursemaids), the chances- that flat-foot will occur are increased.
We now come to the movements of the foot upon the leg. We see here a striking combination of variety of movement with general security. This combination is effected by the harmonious action of three joints, each of which acts in a direction different from the others.
The first of these joints is the ankle-joint, which is formed by the bones of the leg —the tibia and fibula—above and the astragalus below. By this joint, the foot is bent or straightened on the leg. The second joint is between the astragalus and the heel-hone, and it permits the foot to be rolled inwards or outwards; while the third joint is between the first and second row of tarsal bones—namely, between the astra galus and heel-bone behind, and the scaphoid and cuboid bones in front, and allows the degree of curvature of the plantar arch to be increased or diminished within certain limits. The following is the order in which the movements of these three joints occur: the raising of the &et (by the first joint), is accompanied by a rolling of the F. inwards (by the second joint), and by an increased flexure of the plantar arch (by the third joint); and the raising of the toes is accompanirid by a rolling of the foot outwards and a straightening of the sole. See Humphry, op. cit., p. 42.
The joints, however, merely allow of movements; they do not effect them; this is the special function of the muscles; and each of the three movements we have indi cated is effected by special groups of muscles. The first series of movements is mainly effected by three muscles, viz.: (1) the muscles of the calf, attached above to the bones of the thigh and leg, arid below by the tendo Achillis to the heel-bone; (2) the posterior tibial, attached above to the tibia, and below by its tendon to the scaphoid bone; and (3) the short fibular, attached above to the fibula, and below by its tendon to the outer meta tarsal bone The calf-muscles, whose tendon is inserted into the heel-bone, are large and very powerful, for in raising the heel, they have to raise the weight of the body.
The other two muscles, the posterior tibial and the short fibular, turn round the inner and outer ankle respectively, and are inserted into the inner and the outer edges of the instep; the former being attached to the scaphoid, and the latter to the outer metatarsal bone. They not only assist to raise the ankle, but support it laterally. The muscle whose tendon is on the inner side of the F. (the posterior tibial), effects the two move ments which are associated with the raising of the heel-bone, namely, the turning of the F. inwards, and the increased flexure of the arch.
The second series of movements—the raising of the. toes, the turning of the F. outwards, and the straightening of the sole—are effected by two muscles, the anterior tibial and the third fibular, whose tendons pass, one in front of the inner ankle, and the other in front of the outer ankle, to the corresponding edges of the instep, and are inserted into the internal cuneiform and the outermetatarsal bones. These muscles are direct flexors of the tarsus upon the leg; the former raising the inner, and the latter the outer border of the foot.
Another point in the anatomy of the F. that requires notice, is the mode of union of the metatarsal with the tarsal bones. In these joints in the fourth and fifth toes a slight revolving motion can take place, which probably enables the outer metatarsals to adapt themselves to inequalities of the ground, and to equalize the distribution of the weight which is thrown upon the F.; while, in the corresponding joints of the three inner toes, scarcely any motion can occur—a provision by which additional strength is given to the inner side of the F. upon which the weight of the body'most directly 'falls.
The skin of the sole is very tough and strong; and intervening between it and the bones and long plandalar ligament is a thick pad of fat, which acts the part of an air or water cushion in defending the adjacent parts from injurious pressure, and in deaden ing the jars and shocks that would otherwise be felt in leaping, etc.
, A few remarks on the subject of shoes may here be added. in the foot in its normal state, the great toe is free from the others, and the line of its axis prolonged back wards, passes through the center of the heel; while in afoot distorted by the use of a shoe,. the line of the great toe is quite altered, and the toes generally—not being able to find room side by side—overlap each other, and lose their separate and individual actions; corns, *unions, and ingrowing toe-nails being the natural consequence of this maltreat ment. Prof. Meyer, of Zurich, has drawn attention to the bad treatment which the foot receives from ordinary shoemakers, in a pamphlet, translated by.Mr. Craig, and entitled Why the Shoe Pinches: a Contribution to Applied Anatomy. 'He especially points out that the great toe should be allowed to have its normal position, and this can be done by tanking the inner edge of the sole incline inwards, instead of outwards, from the balls of the toes. Dr. Humphrey, from whose admirable work we have drawn much of this article, while fully according in Meyer's views, additionally protests against high heel-pieces, as tending to make the step less steady and secure, to shorten it, and to impair the action of the calf-muscles; a. high heel-piece, moreover, places the forepart of the foot at a lower level than the heel; the weight.is thus thrown too much in the direction of the toes, and they are thrust forwards and cramped against the upper leather of the shoe.
The subjects of WALKING, RUNNING, and JUMPING are noticed in the article