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surface of the lateral malleolus. The distal angle of this area is prominent and somewhat everted, and sometimes referred to as the processus lateralis tali (lateral process). The medial aspect of the body has a comma-shaped facet, confluent with the dorsal articular surface, over the medial edge of the trochlea; this
FIG. 254.-DORSAL SURFACE OF THE BONES OF THE RIGHT FOOT.
articulates with the lateral surface of the medial malleolus. Below this facet the bone is rough and pitted by numerous small openings, and just below the tail of the comma there is a circular impression for the attachment of the deep fibres of the deltoid ligament (talo-tibial fibres). On the plantar surface of the body there is a deep concave facet, called the posterior calcanean facet (facies calcanea
articularis posterior), which is of more or less oval or oblong form and is placed obliquely from behind forwards and laterally; this rests upon a corresponding surface on the dorsal aspect of the calcaneus. In front of this, and crossing the bone from the medial side laterally and forwards, is a deep furrow (sulcus tali),
the floor of which is pierced by numerous large canals.
It serves for the attach
ment of the strong interosseous ligament which unites the talus with the calcaneus, and separates the facet already described from a smaller oval articular area having a slightly convex surface, which lies immediately in front of it. This is called the middle calcanean facet (facies articularis calcanea media), and articulates with
the dorsal surface of the sustentaculum tali of the calcaneus. Posteriorly the body is provided with two tubercles, separated by a groove; the lateral of these (processus posterior tali) is usually the larger, and is occasionally a separate ossicle (os trigonum). To it is attached the posterior talo-fibular ligament of the anklejoint. The groove, which winds obliquely from above downwards and medially over the posterior surface of the bone, lodges the tendon of the flexor hallucis longus muscle.
The head, of oval form, is directed forwards and medially. Its anterior surface
FIG. 256. MUSCLE-ATTACHMENTS TO LEFT TARSUS AND METATARSUS (Plantar Aspect).
is convex from side to side and from above downwards, and articulates with the
The neck, best seen on dorsal surface, passes from the front of the body and
FIG. 258. THE RIGHT TALUS. C. Seen from the lateral side; D. Seen from the medial side.
of the medial malleolar facet, and laterally forms a wide groove, which becomes continuous on the plantar surface with the lateral end of the interosseous groove.
The calcaneus is the largest of the tarsal bones. It supports the talus on its dorsal surface and articulates with the cuboid anteriorly. On the plantar aspect and behind, its posterior extremity, or tuberosity (tuber calcanei), forms the heel, on which so large a proportion of the body weight rests. The long axis of the bone inclines forwards and a little laterally and upwards.
The dorsal surface of the calcaneus is divisible into two parts-a posterior nonarticular part and an anterior articular portion. The length of the former varies according to the projection of the heel; rounded from side to side, it is slightly concave from before backwards. In front of this there is a convex articular area of variable shape (facies articularis posterior), sometimes nearly circular, at other times oval and occasionally almost triangular. This is directed upwards and forwards, and articulates with the posterior calcanean facet on the plantar surface of the talus. Anterior to this facet the bone is deeply excavated, forming a fossa from
Surface for attachment
of long plantar liga. ment
FIG. 259. THE RIGHT CALCANEUS. A. Seen from above; B. Seen from below.
which a groove (sulcus calcanei) leads backwards and medially around the anteromedial border of the articular surface. When the calcaneus is placed in contact with the talus, this groove coincides with the sulcus on the plantar surface of the talus, and so forms a canal or tunnel (sinus tarsi) in which the strong interosseous ligament which unites the two bones is lodged. To the front and medial side of this groove there is an elongated articular facet directed obliquely from behind forwards and laterally, and concave in the direction of its long axis. This is frequently divided into two smaller oval areas by an intermediate nonarticular surface. Of these facets the posterior (facies articularis media) articulates with the middle calcanean facet on the plantar surface of the talus, whilst the anterior (facies articularis anterior) supports the plantar surface of the head of the talus (facies articularis calcanei anterior). The lateral side of the anterior extremity of the dorsal surface of the bone is rough, and to this is attached the origin of the short extensor muscle of the toes.
The plantar surface of the bone is slightly concave from before backwards, and convex from side to side. The plantar aspect of the tuberosity is provided with two tubercles, a medial (processus medialis tuberis calcanei) and a lateral (processus lateralis tuberis calcanei), of which the former is the larger. From the medial process the short flexor of the toes and the abductor hallucis muscle arise, whilst from both tubercles