The posterior tibial artery (Fig. 551) begins at the lower border of the Popliteus, opposite the interval between the tibia and fibula; it extends obliquely downward, and, as it descends, it approaches the tibial side of the leg, lying behind the tibia, and in the lower part of its course is situated midway between the medial malleolus and the medial process of the calcaneal tuberosity. Here it divides beneath the origin of the Adductor hallucis into the medial and lateral plantar arteries.
Relations.—The posterior tibial artery lies successively upon the Tibialis posterior, the Flexor digitorum longus, the tibia, and the back of the ankle-joint. It is covered by the deep transverse fascia of the leg, which separates it above from the Gastrocnemius and Soleus; at its termination it is covered by the Abductor hallucis. In the lower third of the leg, where it is more superficial, it is covered only by the integument and fascia, and runs parallel with the medial border of the tendo calcaneus. It is accompanied by two veins, and by the tibial nerve, which lies at first to the medial side of the artery, but soon crosses it posteriorly, and is in the greater part of its course on its lateral side.
Behind the medial malleolus, the tendons, bloodvessels, and nerve are arranged, under cover of the laciniate ligament, in the following order from the medial to the lateral side: (1) the tendons of the Tibialis posterior and Flexor digitorum longus, lying in the same groove, behind the malleolus, the former being the more medial. Next is the posterior tibial artery, with a vein on either side of it; and lateral to the vessels is the tibial nerve; about 1.25 cm. nearer the heel is the tendon of the Flexor hallucis longus.
Peculiarities in Size.—The posterior tibial is not infrequently smaller than usual, or absent, its place being supplied by a large peroneal artery, which either joins the small posterior tibial artery, or continues alone to the sole of the foot.
Branches.—The branches of the posterior tibial artery are: