The seven tarsals are arranged in two rows. The most proximal row includes the talus and calcaneus, which together transmit most of the weight from the tibia. The distal row includes the three cuneiform bones and the cuboid. The navicular bone is sandwiched between the talus of the proximal row and the cuneiform bones of the distal row.
The talus (called the astragalus in other animals) consists of a convex head which articulates distally with the navicular, and a body which articulates on the plantar surface with the calcaneus and on the dorsal surface with the fibula and tibia. The dorsal surface of the talus is dominated by the trochlea, which articulates with the tibia. The trochlea is locked between the medial malleolus of the tibia on the medial side and the lateral malleolus of the fibula on the lateral side. The lateral side of the trochlea bears a distinct lateral process to accommodate the lateral malleolus. The plantar surface of the talus bears three articular surfaces for the calcaneus. These are the distal, medial and proximal calcaneal articular surfaces. Sometimes the distal and medial surfaces are united in a single larger facet. The proximal calcaneal articular surface is separated from the other articular surfaces by a deep valley, the sulcus tali. To side the talus, note that the head is distal, the trochlea dorsal, and the lateral process is lateral.
The familiar heel bone, or calcaneus, is the largest of the of the tarsal bones. In distal view, the irregularly shaped cuboid articulation is visible. The distal end also bears three dorsally facing talar articular surfaces: the proximal, medial and distal talar articular surfaces. As in the talus, the proximal articular surface is separated from the other surfaces by a deep valley, the sulcus calcanei. The medial side of the talar articular portion of the calcaneus projects medially as the sustentaculum tali. The sustentaculum tali is undercut by a deep groove for flexor hallucis longus a powerful flexor of the big toe. The proximal end of the calcaneus ends in a robust calcaneus tuberosity which serves as the attachment for the common tendon of the soleous and gastrocnemius muscles, powerful plantarflexors of the foot. This common tendon is commonly known as Achilles’ tendon. The dorsal surface of the calcaneus tuberosity bears a broad medial process and a smaller lateral process. To side the calcaneus, note that the plantar surface has no articular facets, the calcaneal tuberosity is proximal, and the sustentaculum tali points medially.
The navicular is a boat-shaped bone. Its morphology is very similar to that of the scaphoid of the hand, but the navicular is much larger, and its distal end bears three articular facets for the three cuneiform bones (medial, intermediate, and lateral). The proximal end of the navicular consists of at deeply concave depression for the head of the talus. Siding the navicular is facilitated by the robust tubercule which projects medially and towards plantar.
The medial cuneiform is the largest of the three cuneiform bones. It has a distinctive kidney-shaped distal articular facet for the first metatarsal. The proximal end bears a small proximally oriented concave facet for the navicular. This navicular articular surface is continuous with the long thin articular surface for the intermediate cuneiform and the second metatarsal. The plantar surface of the medial cuneiform is roughened by a proximal and distal tuberosity. The broad non-articular medial surface is featureless, except for a oval-shaped polished area in the medial and distal corner of the bone which may be mistaken for an articular facet. This oval is in fact polished by the tendon for tibialias anterior. To side the medial cuneiform, note that the distal facet for MT1 is kidney shaped, while proximal facet for the navicular is concave. The dorsal surface is roughened by two tuberosities, and the long thin articular surface of the intermediate cuneiform is lateral.
The intermediate cuneiform is the smallest of the three cuneiforms. It is rectangular in all views except proximal and distal, in which views it is triangular. The distal articular surface for MT2 is slightly convex, while the proximal articular surface for the navicular is concave. The broad and unremarkable surface at the base of the triangle is the dorsal surface. The point of the triangle is on the plantar surface. The medial and lateral surfaces bear facets for the medial and lateral cuneiform, respectively. To side the intermediate cuneiform, the broad, non-articular surface is dorsal and the concave facet is proximal. The facet for the medial cuneiform runs the entire proximal-distal length of the bone, while the facet for the lateral cuneiform does not.
The lateral cuneiform is very similar in shape to the intermediate cuneiform, but is slightly larger. The dorsal surface is broad and unremarkable, while the plantar surface comes to a point. The proximal facet for the navicular is concave, while the distal articular facet for MT3 is more flat. To determine the side, note that the dorsal surface is broader than the plantar surface, and the concave navicular facet is proximal. The lateral facet for the cuboid is a single rounded facet which is larger than the small double facets for the intermediate cuneiform on the medial side.
The cuboid is a large tarsal on the lateral end of the distal tarsal row. The distal end of the bone bears two facets, one each for MT4 and MT5. The proximal end has a single saddle-shaped articular surface for the calcaneus. The dorsal aspect of the bone is broad and undecorated by any named features. The plantar aspect bears a robust cuboid tuberosity with a deep groove for the peroneus longus tendon immediately distal to the tuberosity. The medial aspect of the bone bears an articular surface for the lateral cuneiform. Occasionally, there is a small facet for the navicular. When present, the navicular facet is continuous with the lateral cuneiform facet. To side the cuboid, note that the two metatarsal facets are distal, the dorsal surface is broad and unremarkable, and the medial surface bears the facet for the lateral cuneiform.