The tibial crest running in a curved course downwards from the tibial spine forms a prominent landmark, while its internal surface being subcutaneous is easily palpated throughout its entire length. The fibula is situated distinctly behind the tibia in the greater part of its course, and its head is easily made out, lying a finger's breadth below the knee, with the biceps tendon inserted into it, and the external popliteal nerve lying to the inner side of the biceps tendon, and again crossing the neck, while the lower fourth is subcutaneous, and separates the peroneus tertius in front from the peronei longus and brevis behind. Two lines, drawn respectively from the front and back of the head of the fibula to the anterior and posterior borders of the external malleolus, give the positions of the anterior and posterior peroneal sulci, along which intermuscular septa are given off from the deep fascia, which pass to the anterior and external borders of the fibula. Lying between the tibial crest and the anterior peroneal sulcus are the extensor muscles, anterior tibial vessels, and nerves. Between the two peroneal sulci lie the two principal peroneal muscles and the musculocutaneous branch of the external popliteal nerve, whose other branch, the anterior tibial, perforates the anterior peroneal septum and extensor longus digitorum muscle to reach the extensor compartment. Between the posterior peroneal sulcus and the inner border of the tibia lie the flexor muscles and posterior tibial vessels and nerve. The long internal and short external saphenous veins can generally be made out, the former, accompanied by the long.saphenous nerve, running from the front of the internal malleolus along and internal to the inner border of the tibia, while the latter, accompanied by the external saphenous nerve, runs from behind the outer malleolus along the middle of the calf to the popliteal space. The association of these veins with nerves, as likewise the association of the deep posterior tibial veins with the posterior tibial nerves, is given as a reason for the pain which so frequently accompanies varicose veins. In this connection it may be mentioned that pain referred to the leg may arise from pressure applied to the sciatic trunk or obturator intrapelvically. Thus carcinoma recti may cause pain referred to theknee and leg. Renal calculus is said also sometimes to cause pain referred to the foot. The tibial vessels are given off at the level of the lower margin of the tubercle of the tibia. The course of the anterior tibial is indicated by a line from a point midway between the external tuberosity of the tibia and head of the fibula to the centre of the front of the ankle ; that of the posterior tibial by a line from the centre of the popliteal space to a point midway between the inner malleolus and the prominence of the heel. The posterior tibial is superficial in the lower fourth of the leg, where it lies between the tibia and the tendo Achillis ; it gives off the peroneal 3 inches below the knee, which vessel runs along the posterior surface of the fibula to end behind the outer malleolus.
The skin of the leg generally is more adherent than that of the thigh, and this is particularly the case over the superficial portions of the shafts of the tibia and fibula. A blow on the skin is apt to cut the integument upon the sharp edge of the tibial crest, and injuries and ulcers occurring in this region may readily expose or even involve the bone, old scars frequently being found adherent to the bone. The superficial veins of the leg lie in the subcutaneous tissue, superficial to the deep fascia, while the deep ve┐ns accompany the arteries under the deep fascia, each artery distal to the popliteal having a couple of venae comitÚs. Both groups, but particularly the superficial, are frequently affected by varicosity, owing probably to their dependent position and vertical direction, and the consequently long column of blood they must support ; the possibility of the large abdominal trunks which they ultimately enter being pressed on ; and in the case of the superficial veins the comparative want of support from either deep fascia, or, more important, muscular contraction. The wearing of garters, compressing the veins against the firm, deep fascia, may also influence their occurrence. Normally the circulation in the veins is carried on by the vis a tergo of the heart, the suction action of the chest in inspiration, and muscular action, the intermittent action of the two latter being compensated by the valves in the interior of the veins, which prevent any backward flow. Varicosa first shows itself at these valves, frequently in situations where deep and superficial veins communicate, by a series of dilatations.
Following the dilatation, the valves become incompetent, engorgement follows, and the vein stretches and becomes tortuoufe, while the surrounding skin, suffering from the defective circulation, frequently becomes pigmented, and is prone to ulceration. In some cases the trunk of the internal saphenous (or more rarely the external saphenous) is alone affected, the dilatation extending up to the saphenous opening ; in others the dilatation is general. The deep fascia of the leg, continuous with that of the thigh, invests the whole limb, save where the bones are subcutaneous, where it is interrupted and attached to the bony margins on either side of the subcutaneous portion. It is also attached to the head of the fibula. It is thicker in front than behind, particularly just below the knee, and it is strengthened below at the annular ligaments. Its peroneal septa have already been described.
In the compartment between the tibial crest and the anterior septa are the tibialis anticus and extensor communis digitorum, extensor longus hallucis and peroneus tertius muscles, anterior tibial vessels and nerve, and anterior branch of the peroneal artery. At the upper end of the compartment the two first-named muscles lie together, and are said to be separated from one another by a septum, which is the guide to the underlying vessels. As a matter of fact, the position of the septum has generally to be guessed, and then on separating the muscles the anterior tibial artery, with its venae comites, is found lying on the interosseous membrane. Toward its lower extremity the compartment narrows, and the relation of the muscles alters, the extensor hallucis intervening between the border of the tibialis anticus and the extensor digitorum, the artery therefore below the middle of the leg being sought on the interosseous membrane or anterior surface of the shaft of the tibia between the tibialis anticus and external hallucis. At the ankle the artery is crossed by the tendon of the extensor hallucis, and lies superficially between it and the extensor digitorum. It is continuous with the dorsalis pedis of the foot. Its most important branch is probably the anterior tibial recurrent already mentioned. After ligature of the anterior tibial, the collateral circulation is kept up by the external malleolar of the anterior tibial with the peroneals; the internal malleolar of anterior tibial with posterior tibial ; and the dorsalis pedis and plantar with peroneals.