FIBULA. 160 



of the head is rough, for the attachment, in front, of the anterior superior tibio- 

 fibular ligament, and the upper and anterior part of the Peroneus longus ; and 

 behind, to the posterior superior tibio-fibular ligament, and the upper fibres of the 

 outer head of the Soleus muscle. 



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

 what flattened from without inwards, and is longer, and descends lower, than 

 the internal malleolus. Its external surface is convex, subcutaneous, and con- 

 tinuous with a triangular surface, also subcutaneous, on the outer side of the shaft. 

 The internal surface presents in front a smooth triangular facet, broader above 

 than below, convex from above downwards, which articulates with a correspond- 

 ing surface on the outer side of the astragalus. Behind and beneath the articular 

 surface is a rough depression, which gives attachment to the posterior fasciculus of 

 the external lateral ligament of the ankle. The anterior border is thick and rough, 

 and marked below by a depression for the attachment of the anterior fasciculus of 

 the external lateral ligament. The posterior border is broad and marked by a 

 shallow groove, for the passage of the tendons of the Peroneus longus and Peroneus 

 brevis muscles. Its summit is rounded, and gives attachment to the middle fasci- 

 culus 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 into two 

 lines, which bound the triangular subcutaneous surface immediately above the 

 outer side of the external malleolus. It 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 ; it 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 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 forms the anterior surface. 



The posterior border is sharp and prominent ; it commences above at the bass 

 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 

 forms 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 being 

 continuous with the interosseous ridge at the lower fourth of the bone. It attaches 

 an aponeurosis which separates the Tibialis posticus from the Soleus above, and 

 the Flexor longus pollicis below. This ridge sometimes ceases just before ap- 

 proaching the interosseous 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, is directed outwards in 

 the upper two-thirds of its course, backwards in the lower third, where it is con 

 tinuous with the posterior border of the external malleolus. This surface is com. 

 pletely 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 the bone. 



