THE FIBULA, OR CALF BONE 237 



curving somewhat outward, bifurcates so as to embrace the triangular subcutane- 

 ous 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 (crista interossea}, 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 malleolus. It serves for the attachment of the interosseous membrane, 

 which separates the Extensor muscles in front from the Flexor muscles behind. 



The postero-external border (crista lateralis} 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 (crista medialis} sometimes called the oblique line, 

 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. 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 (fades anterior} 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 origin of three muscles, the Extensor longus digitorum, Peroneus tertius, 

 and Extensor proprius hallucis. 



The external surface (fades lateralis} 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 (fades medialis} is the interval included between the antero- 

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

 for the origin of the Tibialis posticus muscle. 



The posterior surface (fades posterior} 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 origin 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. It opens into the nutrient canal, which is directed downward. 



The Distal or Lower Extremity. The lower extremity, or external malleolus 

 (malleolus lateralis}, is of a pyramidal form, somewhat flattened from without in- 

 ward, and is longer, and descends lower than the internal malleolus. Its external 

 surface is convex, subcutaneous, and continuous with the triangular (also sub- 

 cutaneous) surface on the outer side of the shaft. The internal surface presents 

 in front a smooth triangular facet (fades articularis malleoli}, broader above than 



