114 



BONES OF THE LOWER LIMB. 



the interosseous ridge, into a posterior and upper part, which gives 

 origin to the tibialis posticus, and an anterior and lower part, from 

 which arise the long extensors of the toes and the peroneus tertius, the 

 interosseous membrane being attached to the line between these sur- 

 faces. About the middle of the posterior surface is the medullary 

 foramen directed downwards into the bone. 



THE TARSUS. 



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

 cuboid, scaphoid, and three cuneiform. 



The calcaneum, or os calris, is the largest bone of the foot. Pro- 

 ■jecting downwards and backwards, it fonns the heel. Above it articu- 

 lates 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 tulcr caJcis, presents inferiorly two 

 tid)crcles, 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 



Fig. 103. Fig. 103. — Right Foot, viewed from above, showing 



ITS Dorsal aspect. (A. T. ) ^ 



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

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

 cuneiform ; f/, 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, first, second, and 

 terminal phalanges of tlie second toe. 



.' art .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 

 surlace 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 sustentacu- 

 lum icili, which projects inwards near the an- 

 terior extremity of the bone in a line with its 

 upper surface, and presents inferiorly 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 interosseous ligament, and is con- 

 vex from without inwards and backwards. 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 ti'ansverse direction, with 

 the cuboid bone, and internal to this, in front of the sustentaculum 



