THE FIBULA. 197 



The shaft presents four borders the antero-external, the antero-internal, the 

 postero-external, and the postero-internal ; and four surfaces anterior, posterior, 

 internal, and external. 



The antero-external border commences above in front of the head, runs verti- 

 cally downward to a little below the middle of the bone, and then, curving some- 

 what outward, bifurcates so as to embrace the triangular subcutaneous surface 

 immediately above the outer surface of the external malleolus. This border gives 

 attachment to an intermuscular septum, which separates the extensor muscles on 

 the anterior surface of the leg from the Peroneus longus and brevis muscles on the 

 outer surface. 



The antero-internal border, or interosseous ridge, is situated close to the inner 

 side of the preceding, and runs nearly parallel with it in the upper third of its 

 extent, but diverges from it so as to include a broader space in the lower two-thirds. 

 It commences above, just beneath the head of the bone (sometimes it is quite 

 indistinct for about an inch below the head), and terminates below at the apex of 

 a rough triangular surface immediately above the articular facet of the external 



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malleolus. It serves for the attachment of the interosseous membrane, which sepa- 

 rates the extensor muscles in front from the flexor muscles behind. 



The postero-external border is prominent ; it commences above at the base 

 of the styloid process, and terminates below in the posterior border of the outer 

 malleolus. It is directed outward above, backward in the middle of its course, 

 backward and a little inward below, and gives attachment to an aponeurosis which 

 separates the Peronei muscles on the outer surface of the shaft from the flexor 

 muscles on its posterior surface. 



The postero-internal border, sometimes called the oblique line, commences above 

 at the inner side of the head, and terminates by becoming continuous with the 

 antero-internal border or interosseous ridge at the lower fourth of the bone. It is 

 well marked and prominent at the upper and middle parts of the bone. It gives 

 attachment to an aponeurosis which separates the Tibialis posticus from the Soleus 

 above and the Flexor longus hallucis below. 



The anterior surface is the interval between the antero-external and antero- 

 internal borders. It is extremely narrow and flat in the upper third of its extent ; 

 broader and grooved longitudinally in its lower third ; it serves for the attachment 

 of three muscles, the Extensor longus digitorum, Peroneus tertius, and Extensor 

 proprius hallucis. 



The external surface is the space between the antero-external and postero- 

 external borders-. It is much broader than the preceding, and often deeply grooved, 

 is directed outward in the upper two-thirds of its course, backward in the lower 

 third, where it is continuous with the posterior border of the external malleolus. 

 This surface is completely occupied by the Peroneus longus and brevis muscles. 



The internal surface is the interval included between the antero-internal and 

 the postero-internal borders. It is directed inward, and is grooved for the attach- 

 ment of the Tibialis posticus muscle. 



The posterior surface is the space included between the postero-external and 

 the postero-internal borders ; it is continuous below with the rough triangular 

 surface above the articular facet of the outer malleolus ; it is directed backward 

 above, backward and inward at its middle, directly inward below. Its upper 

 third is rough, for the attachment of the Soleus muscle ; its lower part presents 

 a triangular rough surface, connected to the tibia by a strong interosseous ligament, 

 and between these two points the entire surface is covered by the fibres of origin 

 of the Flexor longus hallucis muscle. At about the middle of this surface is the 

 nutrient foramen, which is directed downward. 



The Lower Extremity, or external malleolus, is of a pyramidal form, somewhat 

 flattened from without inward, and is longer, and descends lower than the internal 

 malleolus. Its external surface is convex, subcutaneous, and continuous with the 

 triangular (also subcutaneous) surface on the outer side of the shaft. The internal 

 surface presents in front a smooth triangular facet, broader above than below, and 



