TARSUS. ASTRAGALUS. 101 



which bound the triangular subcutaneous surface of the external mal- 

 leolus. The external border begins at the base of the styloid process 

 upon the head of the fibula, and winds around the bone, following the 

 direction of the corresponding surface. The posterior border is sharp 

 and prominent, and is lost inferiorly in the interosseous ridge. 



Development. By three centres ; one for the shaft, and one for 

 each extremity. Ossification commences in the shaft soon after its ap- 

 pearance in the tibia ; at birth the extremities are cartilaginous, an 

 ossific deposit taking place in the inferior epiphysis during the second 

 year, and in the superior during the fourth or fifth. The inferior epi- 

 physis is the first to become united with the diaphysis, but the bone 

 is not completed until nearly the twenty-fifth year. 



Articulations. With the tibia and astragalus. 



Attachment of Muscles. To nine; by the head, to the tendon of 

 the biceps and soleus ; by the shaft, its external surface, to the per- 

 oneus longus and brevis ; internal surface, to the extensor longus 

 digitorum, extensor proprius pollicis, peroneus tertius, and tibialis 

 posticus ; by the posterior surface, to the popliteus and flexor longus 

 pollicis. 



TARSUS. The bones of the tarsus are seven in number ; viz. the 

 astragalus, calcaneus, scaphoid, internal middle, and external cuneiform 

 and cuboid. 



The ASTRAGALUS (os tali) may be recognised by its rounded head, 

 a broad articular facet upon its convex surface, and two articular 

 facets, separated by a deep grove, upon its concave surface. 



The bone is divisible into a superior and inferior surface, an external 

 and internal border, and an anterior and posterior extremity. The su- 

 perior surface is convex, and presents a large quadrilateral and smooth 

 facet somewhat broader in front than behind, to articulate with the tibia. 

 The inferior surface is concave, and divided by a deep and rough 

 groove (sulcus tali), which lodges a strong interosseous ligament, into 

 two facets, the posterior large and quadrangular, and the anterior 

 smaller and elliptic, which articulate with the os calcis. The internal 

 border is flat and irregular, and marked by a pyriform articular sur- 

 face, for the inner malleolus. The external presents a large triangular 

 articular facet, for the external malleolus, and is rough and concave in 

 front. The anterior extremity presents a rounded head, surrounded by 



The surface of the shaft upon which the flexor longus digitorum muscle rests. 

 8. The broad groove on the back part of the inner malleolus, for the tendons of 

 the flexor longus digitorum and tibialis posticus. 9. The groove for the tendon 

 of the flexor longus pollicis. 10. The shaft of the fibula. The flexor longus 

 pollicis muscle lies upon this surface of the bone; its superior limit being 

 marked by the oblique line immediately above the number. 1 1 . The styloid 

 process ori the head of the fibula for the attachment of the tendon of the biceps 

 muscle. 12. The subcutaneous surface of the lower part of the shaft of the 

 fibula. 13. The external malleolus formed by the lower extremity of the fibula. 

 14. The groove upon the posterior part of the external malleolus for the ten- 

 dons of the peronei muscles. 



