TARSAL BOXES. 



107 



THE CALCANEUM. 



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

 downwards 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. 



Fig. 100. RIGHT FOOT VIEWED FROM ABOVE, SHOWING Fig. 100. 



ITS DORSAL ASPECT. ^ 



a, scaphoid bone ; 6, astragalus ; c, os calcis ; d, its 

 great tuberosity ; e, internal or first cuneiform ; /, middle 

 cuneiform ; g, external cuneiform ; h, cuboid bone. I to 

 V, the series of metatarsal bones ; 1, 3, first and terminal 

 phalanges of the great toe ; 1, 2, 3, are placed opposite to 

 the first, second, and terminal phalanges of the second toe. 



The large posterior extremity, or tuber calcis, 

 presents inferiorly two tubercles, which rest upon 

 the ground, and the internal of which is the 

 larger : the rest of its surface, looking backwards, 

 is divided into a lower part, which receives the 

 attachment of the tendo Achillis, and an upper 

 part, smooth and less prominent, separated from 

 that tendon by a synovial bursa. The part in 

 front of the tuber forms a slightly constricted 

 neck. The internal surface of the bone, traversed 

 by the plantar vessels and nerves and the flexor 

 tendons, 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, in a line with 

 its upper surface, and presents inffcriorly a groove 

 occupied by the tendon of the flexor longus pollicis. 

 The superior surface presents two articular facets 

 for the astragalus : the anterior of these is placed 



over the sustentaculum, and is flat ; the other, external and posterior to 

 this, and larger, is separated from it by a rough furrow, giving attachment 

 to the inter osseous ligament, and is convex from without inwards and back- 

 wards. In front of this latter facet is a rough depression, from which the 

 extensor brevis digitorum takes origin. The anterior extremity articulates, 

 by a surface slightly concave in the vertical and convex in the transverse 

 direction, with the cuboid bone ; and internal to this, in front of the sus- 

 tentaculum tali, it gives attachment to the inferior calcaneo-scaphoid ligament. 

 The inferior surface, projecting in a rough anterior tubercle, gives attach- 

 ment to the calcaneo-cuboid ligaments. The external surface is subcutaneous, 

 and on the whole smooth, but presents in its fore-part superficial grooves 

 traversed by the tendons of the peronei muscles. 



THE ASTRAGALUS. 



The astragalus or talus, irregular in form, receives the weight of the body 

 from the leg. It articulates with the tibia and fibula above, the os calcis 

 below, and the scaphoid in front. Its longest axis is directed forwards and 

 inwards. Its convex anterior extremity is called the head, and the circular 

 groove behind it the neck. The superior articular surface, placed behind 



