ly described is thereby formed. This region now presents of a
lozenge-shaped form, B J D K, of which the widest diameter, D J, is
opposite the knee-joint. The flexor muscles, C D J, in diverging from
each other as they pass down from the sides of the thigh to those of the
upper part of the leg, form the upper angle of this space; whilst its
lower angle is described by the two heads of the gastrocnemius muscle, E
E, arising inside the flexors, from the condyles of the femur. The
popliteal space is filled with adipose substance, in which are embedded
several lymphatic bodies and through which pass the principal vessels
and nerves to the leg.

In the dissection of the popliteal space, the more important parts first
met with are the branches of the great sciatic nerve. In the upper angle
of the space, this nerve will be found dividing into the peronaeal, I,
and posterior tibial branches, H K. The peronaeal nerve descends close
to the inner margin of the tendon, J, of the biceps muscle; and, having
reached the outer side of the knee, I*, Plate 66, below the insertion of
the tendon into the head of the fibula, winds round the neck of this
bone under cover of the peronaeus longus muscle, S, to join the anterior
tibial artery. The posterior tibial nerve, H K, Plate 65, descends the
popliteal space midway to the cleft between the heads of the
gastrocnemius; and, after passing beneath this muscle, to gain the inner
side of the vessels, H*, Plate 66, it then accompanies the posterior
tibial artery. On the same plane with and close to the posterior tibial
nerve in the popliteal space, will be seen the terminal branch of the
lesser sciatic nerve, together with a small artery and vein destined for
distribution to the skin and other superficial parts on the back of the
knee. Opposite the heads of the gastrocnemius, the peronaeal and
posterior tibial nerves give off each a branch, both of which descend
along the mesial line of the calf, and joining near the upper end of the
tendo Achillis, the single nerve here, N, Plate 65, becomes superficial
to the fascia, and thence descends behind the outer ankle to gain the
external border of the foot, where it divides into cutaneous branches
and others to be distributed to the three or four outer toes. In company
with this nerve will be seen the posterior saphena vein, L, which,
commencing behind the outer ankle, ascends the mesial line of the calf
to join the popliteal vein, G, in the cleft betw