At the back part of the leg, the aponeurosis is a continuation of that of the ham. We may consider it as formed of two principal layers; one superficial, and the other deep. Attached to the posterior border of the fibula externally, and to the inner margin of the tibia internally. the first appears to arise from the expansion o the tendons of the sartorius, gracilis, and senn tendinosus. Applied over the posterior surface of the calf, it is lost below in the fibro-cellular tissue surrounding the heel. This portion being thin and yielding, it allows deep-seated ab scesses to become superficial with great facility. 1 The second layer is a continuation of the app.., neurosis of the popliteal cavity, and descends between the two layers of muscles ; but split ting into two, at the point where the soleus de taches itself from the deep parts, one of its divisions follows the anterior surface of the tendo Achillis, of which it completes the fibrous canal, formed posteriorly by the super ficial layer; the other remains applied over the posterior surface of the deep muscles, and both arrive at the heel.
In its inferior third, this aponeurosis thus circumscribes three spaces. One is filled by the tendon of the muscles of the calf. The se cond incloses the flexor muscles of the toes, and the vessels. The third, which separates the two others, lies between the tendo Achillis and the posterior surface of the last-named muscles. The latter is remarkable, from being filled with fat and fibrous filaments, interlaced in various directions" We have, for convenience of description, de tailed the anatomy of the superficial parts of the leg, without particular reference to the re gional divisions, which become more defined, distinct, and practical as we investigate the re lations of the deeper seated parts, and to which we shall therefore now limit ourselves.
In the anterior region, comprising all those muscles which rest upon the tibio-fibular fossa, we find, on dissecting the fascia from the upper part, only two muscles exposed, viz. the tibialis anticus and extensor communis digitorum. Lower down, we see in addition the extensor proprius pollicis coming out between the two last, and the peroneus tertius a slip of the outer side of the extensor cotntnunis. These four are, as it were, bound down in a canal, formed anteriorly by the aponeurosis, posteriorly by the tibia, fibula, and interosseous ligament. The direction of the tibialis anticus, its size, and boundaries should be borne in mind, as these form the surest guide for cutting down upon the anterior tibial artery. This muscle is of a prismatic form, tapering downwards, and its outer edge is indicated externally by a sulcus in the integuments made more apparent by extension of the foot. It is found more ac curately by tracing a line from the middle of he space between the crest of the tibia rid the fibula to the middle of the instep; and iere, between this muscle and the extensor ommunis, the artery runs. The external mus ics are the peronei longus and brevis ; they are enveloped in a sheath of the aponeurosis, and are applied, for some extent, to the exter .al surface of the fibula. They are completely epamted from the extensors and from all the uscles of the posterior region by the two apo eurotic septa attached to the anterior and osterior edges of the bone. The adherence of e muscular fibres continuing until just above e outer malleolus, a transverse section, in the wo superior thirds, does not entirely destroy eir action upon the foot, while, lower down, would render abduction almost impossible.
Ye have not heard of an instance of the entire pture of any of these muscles, nor is it an ccident likely to occur, as they are not, from 'teir situation, likely to be called upon for any ery great exertion of power; but these muscles re occasionally liable to the accidental rupture of some of their fibres, a circumstance attended with ranch more pain and distress in moving than the apparently slight nature of the accident might lead us to expect. We have had lately a case of this kind under our care, where the suffering and the injury to the movements of the foot were so great as at first to lead us to suspect a much more serious extent of injury than really existed. It was occasioned by at tempting to push along a sack of corn with both knees, both feet being on the ground, and the heels raised, while the upper part of the sack was held in the arms.
The only artery of importance in this region is the anterior tibial. It commences from the trunk of the popliteal nearly at right angles, traverses the opening in the upper part of the interosseous ligament, arse to the neck of the fibula, and below the head of the tibia. The angular curve which the artery makes at this part of its course, according to M. Ribes, ac counts for the great retraction of it after ampu tation of the leg.* It descends upon the inter osseous ligament, in the direction of a line drawn from the middle of the space between the head of the fibula and the crest of the tibia, to the middle of the instep. Through the upper part of its course it lies upon the in terosseous ligament; as it descends it gradually advances upon the tibia, and runs upon the anterior surface of this bone through its lower third. It is found at the upper third of the leg, between the tibialis anticus and extensor communis digitorum ; in the middle third, its course is between the tibialis anticus and the extensor longus pollicis, and about four inches above the ankle-joint it passes obliquely under the tendon of this last muscle, arid then is found between its tendon and that of the ex tensor communis. It runs between two veins through its whole course. The nerve is on its outer side above; in front in the middle; and internal below. An extensible but resistant cellular sheath unites the whole. It is evident, that in the upper part of its course the artery will be found much deeper than at the lower, when it is lying among the tendons, but in the living subject the natural state of tension of the muscles keeps these tendons more elevated than after death, and we shall consequently find the artery, even in this situation, deeper than from dissection we might have been led to an ticipate. The surgeon will find little difficulty in discovering this artery when it is required to be tied. The marks for his guidance are clear, and the situation of the vessel on the whole pretty uniform ; but owing to the depth of its situation above, and to the immediate vicinity of the veins and nerve, some difficulty will be experienced in excluding these from the liga ture. The only branch from it of any surgical importance is the recurrent tibial. This arises just after the trunk has passed through the in terosseous ligament, and passes upwards in nu merous branches to the 'parts below and to the outer side of the knee-joint, anastomosing freely with the inferior external articular artery. These anastomoscs form an important part of that system of collateral circulation by which the stream of blood is continued to the leg and foot, after the obliteration of the popliteal artery.