size arising from the lower three fourths of the fibula, N, and will be found overlapped by this muscle on the outer border of the tendo Achillis, as low down as the outer ankle. The two arteries are accompanied by venae comites, which, with the short saphena vein, form the popliteal vein. The posterior tibial artery is closely followed by the posterior tibial nerve. In the popliteal space, this nerve crosses to the inner side of the posterior tibial artery, where both are about to pass under the gastrocnemius muscle, to which they give large branches. Near the middle of the leg, the nerve recrosses the artery to its outer side and in this relative position both descend to a point about midway between the inner ankle and calcaneum, where they appear having the tendons of the tibialis posticus and flexor longus digitorum to their inner side and the tendon of the flexor longus pollicis on their outer side. Numerous branches are given off from the nerve and artery to the neighbouring parts in their course. The varieties of the posterior crural arteries are these--the tibial vessel, in some instances, is larger than usual, while the peronaeal is small, or absent; and, in others, the peronaeal supplies the place of the posterior tibial, when the latter is diminished in size. The peronaeal has been known to take the position of the posterior tibial in the lower part of the leg, and to supply the plantar arteries. In whatever condition the two vessels may be found, there will always be seen ramifying around the ankle-joint, articular branches, which anastomose freely with each other and with those of the anterior tibial.