to form the outer ankle. A knowledge of this relative bearing of the two bones is important in the adjustment of fractures, but more especially in the performance of flap-amputations; and for this reason, that the knife, introduced from the tibial side, is apt, unless

F

FIG. 37.

T

properly directed, to pass between the two bones, instead of behind them: and this is the more likely, since the plane of the posterior surface of the tibia slants considerably in front of the fibula. The relative position of the two bones, as well as their relative thickness, are

shown in the adjoining woodcut (fig. 37). The dotted lines represent the interosseous ligament.

HEAD.

The upper end of the fibula is called its "head," and can be felt plainly beneath the skin. On its inner side is the small oval surface which articulates with the tibia. Its outer side is very prominent, and rises behind into a short projection termed the "styloid process." This little process apparently insignificant, is really significant, because it tallies with the olecranon. It forms a little lever* for the insertion of the biceps (one of the hamstring muscles). Besides this the outer part of the "head" gives attachment to the external lateral ligament of the knee-joint.

SHAFT.

The shaft of the fibula is more easy to understand when connected to the tibia. Immediately below the head, the shaft is rounder and thinner than elsewhere. The lower three-fourths of the shaft is triangular, like that of the tibia, for the more convenient origin and course of the muscles. Its three surfaces are placed so, that one (internal) looks towards the tibia; another looks outwards; the third looks backwards. The inner or tibial surface is divided into two unequal parts by a longitudinal ridge. Observe this ridge carefully, because it gives

* Owen proposes to call the styloid process the "fibella." To see this developed into a lever of great power, look at the skeleton of the Echidna.

attachment to the interosseous ligament which divides the muscles on the front from those on the back of the leg. Now the grooved surface behind the ridge in question gives origin to part of the "tibialis posticus;" that in front of it gives origin to the "extensor communis digitorum," (which arises also from the head of the fibula and even the tibia,) to the "extensor proprius pollicis," and to the "peroneus tertius." Thus, four muscles arise from the inner side of the shaft; namely, three in front of the interosseous membrane, and one behind it.

The outer surface of the shaft gives origin to the "peroneus longus" and "brevis." Towards the lower end of the bone this surface inclines backwards, because the tendons of these two muscles play along the groove behind the external malleolus.

The posterior surface gives origin to two muscles only; namely along its upper third to the "soleus," and its lower two-thirds to the "flexor longus pollicis." Here we observe the canal for the medullary vessels: like that in the tibia, it runs downwards.

With regard to the angles of the shaft, the anterior is the sharpest, like that of the tibia. Trace it down the bone, and you will find that it bifurcates about three inches from the lower end, and encloses a triangular surface, which is subcutaneous. Here we feel for fractures of the lower part of the fibula. The other angles do not require special notice.

LOWER END.

The lower end of the fibula descends below the tibia in order to form the "malleolus," for the security of the ankle-joint on the outer side. It is not only longer than the inner malleolus, but projects more, so as to give more power to the tendons of the "peronei," which play in a groove behind it. On its inner side is the smooth, slightly convex surface which articulates with the side of the astragalus; and just above this is the rough surface which fits into the groove of the tibia, and gives attachment to the interosseous ligament which rivets the two bones together. The apex gives attachment to the external lateral ligament of the ankle. On the inner side of the apex is a deep hollow for the attachment of the transverse ligament of the ankle.

The tibia and fibula are so fixed together at the ankle, that there

is no sensible motion between them, only just enough to give a sort of elasticity which yields to slighter sprains. The office of guarding the ankle is performed so well by the fibula, that lateral dislocation cannot take place unless the fibula be broken. Fractures of the fibula generally occur about 2 inches from the lower end, and most frequently happen in consequence of a very violent outward twist of the foot. The outer surface of the os calcis comes to press against the end of the fibula; the result of which is, that the shaft of the bone gives way at the weakest part—that is, just above the ankle. The same accident may happen from a violent twist of the foot inwards: but in this case it is the astragalus, which, by its pressure outwards, causes the fibula to give way. This kind of fracture, accompanied, as it usually is, with more or less injury to the internal lateral ligament of the ankle, or possibly with fracture of the tip of the internal malleolus, is by far the most frequent dislocation about the ankle received into a London Hospital. Such an accident is commonly called "Pott's fracture," after the surgeon who first accurately described it.

The fibula has three centres of ossification; one for the shaft and one for each end. The lower end begins to ossify about the second year; the upper about the third or fourth. Contrary to the rule, the lower end unites the first to the shaft; the reason of this exception would appear to be the necessity of the early solidity of the ankle-joint.

THE BONES OF THE FOOT.

(Plates XXXVII. and XXXVIII.)

"

There are twenty-six bones in the foot. In the tarsus, seven,— namely, the "astragalus," "os calcis," "os scaphoides," three "cuneiform bones," and the "os cuboides;" in the metatarsus, five: the remaining fourteen belong to the toes.

The first question that arises, is, why should there be so many bones in the foot? The answer is the same for the foot as for the hand, in order that there may be so many joints. The structure of a joint not only permits motion, but confers elasticity. Suppose there had been only a single bone, like a shoemaker's last, instead of seven in the tarsus, how much more liable it would have been to fracture and dislocation!

Double arch of the foot.

The bones of the foot form a double arch; an arch from before backwards, and an arch from side to side. The arch is supported, behind, by the os calcis, and in front by the ends of the metatarsal bones. Its height and span are greatest on the inner side of the foot; and gradually decrease towards the outer side. The weight of the body falls perpendicularly on the astragalus, which is the key-bone or crown of the arch. Concerning the astragalus, two points must be always borne in mind:-1, a part (the head) of it is supported below by an elastic ligament (calcaneo-scaphoid), which admits of its rising and falling like a spring; 2, it is articulated with the os calcis and the scaphoid in such a way as to allow the lateral motions of the foot (adduction and abduction). Flexion and extension of the foot, observe, is performed at the ankle-joint. But, besides these beautiful provisions, all the bones of the foot are more or less moveable on each other, so as to break shocks and increase elasticity; and yet their mutual connection is so well provided for, that dislocation of any one bone is extremely rare.

It is wonderful what habit and necessity will make the foot accomplish. We who coop it in tight boots, can hardly believe when we hear of persons carving, writing, and even painting with the toes. "Pes altera manus is not so far off the mark. Not long ago, a French artist, Ducornet (né sans bras), died, who used to paint with his toes pictures worthy of a place in the French Exhibition.

The foot a lever

The foot is a lever for raising the body. It of the first order. is generally described as a lever of the second order; that is, with the fulcrum at the toes. But this is not correct. The foot is a lever of the first order. The fulcrum (which

is a moveable one), is at the ankle-joint F, (cut, fig. 38); the weight

W

FIG. 38.

W is at the toes; and the power (which is the contraction of the muscles of the calf) is at the heel P. All the conditions are those of a lever of the first order. The power and the P weight act in the same direction on opposite sides of the fulcrum. The pressure upon the fulcrum is equal to the sum of the pressures applied, i. e. Px F+W× F.

THE ASTRAGALUS.

(Plate XXXVII.)

The astragalus (àoтpáyaños, talus, the huckle-bone, with which the ancients used to play at dice,) is the key-stone of the arch of the foot, and supports the whole weight of the body, which falls. perpendicularly upon it from the tibia. As it is the chief bone concerned in the mechanism of the spring of the foot, the Germans do well to call it the "spring bone." To examine it thoroughly we must make six aspects.

Its superior aspect, broad and horizontal, the best adapted for the erect posture, is convex from before backwards, so as to articulate with the tibia, and admit of the flexion and extension of the ankle. Observe that this pulley-like surface is at least one-fifth of an inch broader in front than behind. The object of this is to prevent a dislocation of the astragalus backwards, which would otherwise be a more frequent occurrence, considering the direction of the force in walking, running, or leaping. In consequence of this greater narrowness of the astragalus behind, the ankle-joint admits of a very slight lateral movement at the ankle, when the foot is extended. But there can be no lateral movement at the