732 MAMMALIAN ANATOMY 



The Lower Extremity is called the external malleolus. Its shape 

 is that of a pyramid ; the truncated apex is above and applied to the 

 end of the shaft, and the base is below. The pyramid is flattened 

 transversely, presenting a large inner surface and smaller anterior- 

 external and posterior-external surfaces. 



The inner surface (Fig. 555) is almost triangular. The lower 

 margin or base of the triangle is transverse and faintly emarginate, 

 the anterior and posterior margins are straight and slope from the 

 distinct rounded angles upward toward the median line of the shaft. 

 The inner surface is marked near the lower edge and behind the 

 middle line by a deep, irregularly oval pit, in which and to the ad- 

 jacent posterior angle is attached the strong ligament to the astragalus. 

 Above this pit the surface is rough for the attachment of tibio-fibular 

 ligaments. The anterior lower part of the surface is occupied by a 

 large triangular articular facet, the edges whereof are sharply defined. 

 The base of the triangle is vertical, one side formed by the lower 

 margin and the other arching downward and forward to the anterior 

 angle of the malleolus. The surface of the facet is transversely gently 

 convex, and vertically concave above and convex below. It faces 

 almost directly inward, is covered with cartilage, and is applied to the 

 facet on the side of the astragalus. Above this facet is another smaller 

 articular surface, which on the dried bone is not always clearly 

 marked, but is very evident on a fresh bone. Its shape is also 

 triangular ; the base is on the anterior margin, and the apex points 

 backward. Its plane slopes outward, upward, and forward from the 

 other facet, and its surface therefore faces upward, forward, and inward. 

 It is faintly concave from above downward, and fits on the convex 

 facet on the posterior outer part of the lower extremity of the tibia. 



The anterior-external surface (Fig. 554) is long and narrow, but 

 wider below than above. It is bounded in front by the anterior 

 margin of the malleolus, behind by the continuation downward of the 

 anterior border of the shaft, and below by the distal margin. It is 

 gently convex from above downward, and faintly convex from side to 

 side ; it is rough for the attachment of ligaments, and faces outward 

 and forward. The lower end of its posterior border widens, and is 

 produced downward and backward into a prominent flat hook, which is 

 the lowest point of the fibula and is known as the external malleolus 

 proper. Its oval, flat external surface and its edges furnish attach- 



