

BONES OF LOWER LIMB 49 



The Upper Extremity is irregularly rounded, and has on its 

 internal surface a facet for articulation with the tibia, and just 

 .above this is a pointed process the styloid process. 



The Shaft is very irregular in shape and twisted on itself, but 

 .a very narrow anterior surface can be distinguished between 

 the interosseous and external borders. The external border 

 splits below to form a triangular subcutaneous area on the 

 outer malleolus, and behind this line is the external surface. 

 The surface next the external surface is the posterior surface, 

 which is divided by a sharp ridge. (This ridge may be mistaken 

 for the interosseous ridge, but that can be determined by follow- 

 ing up the line from the triangular surface on the malleolus. 

 This line is the external border of the anterior surface.) 



The Lower Extremity is flattened and expanded to form the 

 -external malleolus, on the internal surface of which is the facet 

 for articulation with the outer surface .of the astragalus. Just 

 behind this facet is the digital fossa for the insertion of a 

 ligament. 



Ossification is similar to that of the tibia, except that the 

 centre for the shaft is the only one that appears before birth. 



The Tarsus is composed of seven bones the astragalus, os 

 'calcis, scaphoid, cuboid, and three cuneiforms. 



The Astragalus is the uppermost bone, and, articulating with 

 the tibia and fibula, supports the weight of the body. It is 

 of irregular cubical form, and on the upper, inner, and outer 

 surfaces is one large confluent articular facet, fitting into the 

 ;space enclosed by the under surface of the tibia, and the two 

 malleoli. This facet is saddle-shaped, and is broader in front 

 than behind. Anteriorly is a somewhat constricted neck sup- 

 porting the rounded head, which articulates with the scaphoid 

 bone. On the inferior surface is a large concave facet for 

 articulation with the os calcis. A deep groove divides this facet 

 into two parts, the anterior part articulating with the susten- 

 taculum tali, while the posterior part rests on the body of the 

 os calcis. A strong interosseous ligament is inserted in this 

 groove. Posteriorly the bone is divided by a groove, oblique 

 from above downwards and inwards, into two tubercles. In 

 the groove runs the tendon of tibialis posticus. 



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