THE TARSUS. 



129 



tuberosity of the tibia. The shaft is covered by muscles, except over the tri- 

 angular surface above mentioned. The external malleolus descends lower and pro- 

 jects farther backwards than the internal, its point being nearer to the heel by 

 about three-quarters of an inch. 



THE TARSUS. 



The tarsus is composed of seven bones, viz., the calcaneum, astragalus, navi- 

 cular, three cuneiform, and cuboid. 



The calcaneum or os calcis is the largest bone of the foot, Projecting down- 

 wards and backwards, it forms the heel. Above, it articulates with the astragalus, 

 and in front with the cuboid bone. Its principal axis extends forwards and 

 outwards from its posterior extremity to the cuboid bone. 



The large posterior extremity, or tuberosity, presents inferioiiy two tubercles, which 

 rest upon the ground, and of which the internal is the larger : its hinder surface is 



Fig. 144. THE BONES OF THE RIGHT FOOT : A, FROM ABOVE ; B, FROM BELOW. (Allen Thoinsoii.) ^ 



a, navicular bone ; b, astragalus ; c, os calcis ; d, its tuberosity ; e, internal cuneiform ; /, middle 

 c'.ineiform ; g, external cuneiform ; h, cuboid bone ; I to V, the metatarsal bones ; 1, 3, first and last 

 phalanges of the great toe ; 1, 2, 3, first, second, and third phalanges of the secon-.l toe. 



divided into an upper part, smooth and separated by a bursa from the tendo Achillis, 

 a middle part for the attachment of the tendon, and a lower part, convex and 

 roughened, continued below onto the tubercles, and covered by the thick skin and 

 fatty pad of the heel. The part in front of the tuberosity forms a slightly con- 

 stricted neck. The internal surface of the bone is deeply concave, and its concavity 

 is surmounted in front by a flattened process, the sustentaculum tali, which projects 

 inwards near the anterior extremity of the bone on a level with its upper surface, 

 and presents inferiorly a groove occupied by the tendon of the flexor longus hallucis. 

 The upper surface has two articular facets for the astragalus, separated by an 

 oblique groove in which the interosseous ligament is attached ; the anterior facet, 



