THE FIBULA 105 



flexor longus pollicis. The external surface of the extremity 

 is hollowed for the fibula, and rough for ligaments except 

 along the lower border. Below is an articular surface, quadri- 

 lateral, concave, narrower behind than in front. It shows a 

 slight median elevation separating two lateral depressions. 

 Internally the cartilaginous surface is continued upon the inner 

 malleolus. 



The Fibula 



The fibula (clasp), or peroneal bone, nearly equals the tibia 

 in length; its purpose in the leg is mainly for elasticity. Its 

 shaft is convex backward, and its lower extremity is placed 

 a little in advance of the upper. 



The upper extremity, or head, is prolonged upward at its 

 back part into the styloid process; inside this is a facet looking 

 upward, inward, and forward for articulation with the tibia; 

 more externally is a slight excavation for the biceps; the pero- 

 neus longus is attached in front and the soleus behind. A 

 somewhat constricted part below the head is the neck. 



The lower extremity, or external malleolus, is pyramidal and 

 longer than the internal malleolus; internally it shows a tri- 

 angular, smooth, articular surface for the astragalus, and 

 behind this a depression for the posterior band of the external 

 lateral ligament. 



Posteriorly is a shallow groove for the peroneus longus 

 and brevis tendons. Externally this extremity is convex and 

 subcutaneous. 



The shaft presents four surfaces anterior, posterior, internal, 

 and external; and four borders anteroexternal, anterointernal, 

 posteroexternal, and posterointernal. (Gray.) 



The anteroexternal border begins in front of the head and 

 bifurcates below to embrace the triangular subcutaneous 

 surface of the external malleolus; this border is between the 

 peroneal and extensor muscles. 



The anterointernal border, or interosseous ridge, is close to 

 the preceding and parallel with it in the upper third. It ter- 

 minates below at the apex of a rough surface just above the 

 articular facet. The attached interosseous membrane separates 

 the extensors in front from the tibialis posticus behind. 



The posteroexternal border commences at the base of the 

 styloid process and terminates below in the posterior border 



