ries in their upper two thirds; but as these muscles taper
towards the mesial line where they end in the tendo Achillis, V V, Plate
65, they leave the posterior tibial artery, O, with its accompanying
nerve and vein, uncovered in the lower part of the leg, except by the
skin and the superficial and deep layers of fasciae. The peronaeal
artery is deeply situated in its whole course. Soon after its origin, it
passes under cover of the flexor longus pollicis, R, a muscle of large
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.

The popliteal artery is unfavourably circumstanced for the application
of a ligature. It is very deeply situated, and the vein adheres closely
to its posterior surface. Numerous branches (articular and muscular)
arise from it at short intervals; and these, besides being a source of
disturbance to a ligature, are liable to be injured