248 THE SKELETON. 



neus Longus and Peroneus Brevis muscles. The summit is rounded, and gives 

 attachment to the middle fasciculus of the external lateral ligament. 



The Shaft presents three surfaces and three borders. The anterior border com- 

 mences above in front of the head, runs vertically downwards to a little below 

 the middle of the bone, and then, curving a little outwards, bifurcates below. 

 The two lines so formed bound the triangular subcutaneous surface immediately 

 above the outer side of the external malleolus. This border gives attachment 

 to an intermuscular septum, which separates the muscles on the anterior surface 

 from those on the external. 



The 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 ex- 

 ternal malleolus. It serves for the attachment of the interosseous membrane, 

 and separates the extensor muscles in front from the flexor muscles behind. 

 The portion of bone included between the anterior and interosseous lines forma 

 the anterior surface. 



The posterior border is sharp and 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 outwards above, backwards in the middle of its course, 

 backwards and a little inwards below, and gives attachment to an aponeurosis 

 which separates the muscles on the outer from those on the inner surface of 

 the shaft. The portion of bone included between this line and the interosseous 

 ridge, and which includes more than half of the whole circumference of the 

 fibula, is known as the internal surface. Its upper three-fourths are subdivided 

 into two parts, an anterior and a posterior, by a very prominent ridge, the 

 oblique line of the fibula, which commences above at the inner side of the head, 

 and terminates by becoming continuous with the interosseous ridge at the 

 lower fourth of the bone. The oblique line attaches an aponeurosis which 

 separates the Tibialis Posticus from the Soleus above, and the Flexor Longus 

 Pollicis below. This line sometimes ceases just before approaching the inter- 

 osseous ridge. 



The anterior surface is the interval between the anterior and interosseous 

 lines. 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 

 Longus Pollicis. 



The external surface, much broader than the preceding, and often deeply 

 grooved, is directed outwards in the upper two-thirds of its course, backwards 

 in the lower third, where it is continuous with the posterior border of tin 

 ternal malleolus. This surface is completely occupied by the Peroneus Longus 

 and Peroneus Brevis muscles. 



The internal surface is the interval between the interosseous ridge and the 

 posterior border, and occupies nearly two-thirds of the circumference of th 

 bone. Its upper three-fourths are divided into an anterior and a posterior portio 

 by a very prominent ridge already mentioned, the oblique line of the fibul 

 . The anterior portion is directed inwards, and is grooved for the attachment o 

 the Tibialis Posticus muscle. The posterior portion is continuous below wit! 

 the rough triangular surface above the articular facet of the outer malleolus 

 it is directed backwards above, backwards and inwards at its middle, directly 

 inwards below. Its upper fourth is rough, for the attachment of the Soleu 

 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 Pollicis muscle. 





