medial side of the foot
from behind forward may be felt the _medial process (internal
tuberosity)_ of the calcaneus; the _sustentaculum tali_, which lies
about 1 inch vertically below the tip of the malleolus; the _tubercle
of the navicular_, about 1 inch in front of the malleolus, and at a
slightly lower level; the _first (internal) cuneiform_, and the base,
shaft, and head of the _first metatarsal_.

On the lateral side may be recognised the _lateral process (external
tuberosity)_ of the calcaneus; the _trochlear process (peroneal
tubercle)_ on the same bone; the _cuboid_; and the prominent base of
the _fifth metatarsal_.

The talo-navicular joint lies immediately behind the tuberosity of the
navicular, and a line drawn straight across the foot at this level
passes over the calcaneo-cuboid joint.

The _ankle-joint_, formed by the articulation of the tibia and fibula
with the talus, lies about half an inch above the tip of the medial
malleolus, and is so constructed that when the foot is at a right
angle with the leg it is only possible to flex and extend the joint.
When the toes are pointed, however, slight side-to-side and rotatory
movements are possible. The chief seat of side-to-side movement of the
foot is at the talo-navicular and calcaneo-cuboid articulations--"the
mid-tarsal or Chopart's joint."

The ankle-joint owes its strength chiefly to the malleoli and the
collateral ligaments, and to the inferior tibio-fibular ligaments,
which bind together the lower ends of the bones of the leg. The
numerous tendons passing over the joint on every side also add to its
stability.

The synovial membrane of the ankle-joint passes up between the bones
of the leg to line the inferior tibio-fibular joint; but it is
distinct from that of the intertarsal joints, which communicate with
one another in a complicated manner. The epiphysial cartilage at the
lower end of the fibula lies on the level of the talo-tibial
articulation, while that of the tibia is about half an inch higher
(Fig. 93).

[Illustration: FIG. 93.--Section through Ankle-Joint showing relation
of epiphyses to synovial cavity.

_a_, Lower epiphysis of tibia.
_b_, Lower epiphysis of fibula.
_c_, Talus.
_d_, Calcaneus.

(After Poland.)]

FRACTURES IN THE REGION OF THE ANKLE

#Pott's Fracture.#--It must be understood that various lesions
occurring in the region of the ankle-joint are included under the
clinical term "Pott's fracture