PELVIC LIMBS 719 



the shaft and representing its upper limit, and the other side the 

 internal border. The posterior surface is gently convex transversely, 

 and affords attachment to the posterior ligament of the ankle-joint. 

 The lower margin is swollen in the middle, and its internal half is 

 marked by a wide, shallow groove for the tendon of the flexor longus 

 hallucis. The external half, with the part of the posterior surface of 

 the shaft above it, is occupied by a concave triangular articular facet 

 for the lower extremity of the fibula. This facet faces backward and 

 outward. 



The lower or distal surface (Fig. 548) is divided by a change 

 in the direction of its plane into (1) a smaller internal part and (2) a 

 larger external part. 



(1) The internal part is the median surface of the internal mal- 

 leolus, and faces downward, but principally outward. Its lower margin 

 is arcuate ; its upper margin is not well defined ; the surface here passes 



FIG. 548. 



With Astragalus. 



Internal Malleolus of Tibia (ffl ?|j Groove for Tendon of PERONEUS 



Groove for Tendon of TIBIALIS fill <JL*$L^' 



.^vvi \-Jr I Ml 1 External Malleolus of Fibula. 



Groove for Tendon of FLEXOR ^-" *^<^ i^^ \^^\J 



Surface for Tendon of FLEXOR LONGUS HALLUCIS. Groove for Tendons of PERONEUS BREVIS 



and PERONEUS TERTIUS. 



LEFT TIBIA AND FIBULA, DISTAL ASPECT. 



into the external part of the distal surface. About half-way up on 

 the median surface of the malleolus is a line which runs upward and 

 backward to the middle, then bends nearly at a right angle and runs 

 downward and backward. The surface included between the lower 

 border and this line is a segment of a circle, and is slightly concave 

 in both directions ; it is rough, and is occupied by a strong ligament 

 attached to the astragalus. Above this bent line the surface is smooth, 

 and articulates with the upper part of the inner surface of the astragalus. 



(2) The external part of the distal surface is smooth and covered 

 with articular cartilage. It is divided by a slightly curved ridge into 

 two lateral concave parts, which fit the two convex parts on each side 

 of the median groove on the dorsal surface of the astragalus. The 

 dividing ridge begins in front, at the apex of the triangular anterior 

 surface, and runs obliquely backward and inward to end in the middle 



