THE FIBULA. 253 



body. It is the district bounded laterally by the lateral crest and medially by 

 the medial crest and the, distal fourth or fifth of the interosseous crest. It is 

 twisted in the same degree as the lateral surface ; and, therefore, while its proximal 

 part is directed backwards, its distal part is directed medially and is in line with 

 the medial surface of the malleolus. The nutrient foramen is situated on the 

 posterior surface, at or near the middle of the body near the medial crest, and 

 is directed towards the distal end of the bone. 



The anterior crest gives attachment to the anterior intermuscular septum, and, 

 at its distal end, to the ligamentum transversum cruris, while the posterior inter- 

 muscular septum is attached to the lateral crest. These septa enclose the peroneus 

 longus and brevis muscles, which arise from the lateral or peroneal surface, and 

 separate them from the muscles on the front and the back of the leg. The inter- 

 osseous membrane is attached to the whole length of the interosseous crest. The 

 anterior part of the- medial surface provides origin for the extensor halluciis, the 

 extensor digitorum longus and the peroneus tertius; while the tibialis posterior 

 arises from the posterior part of the medial surface. The medial crest is the fibular 

 attachment of a strong sheet of fascia which covers the tibialis posterior, and 

 separates it from the flexors of the toes. The soleus muscle arises from the 

 proximal third of the posterior surface, while the flexor hallucis longus takes 

 origin from its distal two -thirds. 



The distal extremity of the fibula, or lateral malleolus, is of pyramidal 

 form. Its medial surface is furnished with a triangular articular area (facies 

 articularis malleoli), plane from before backwards, and slightly convex proximo- 

 distally, which articulates with a corresponding surface on the lateral side of the 

 body of the talus. Behind this there is a deep pit, to which the posterior 

 talo- fibular ligament is attached. Proximal to the articular facet there is a rough 

 triangular area, from the summit of which the interosseous crest arises ; to this 

 are attached the strong fibres of the distal interosseous ligament which binds 

 together the opposed surfaces of the tibia and fibula. The lateral surface of the 

 distal extremity forms the elevation of the lateral malleolus which determines the 

 shape of the projection of the lateral ankle. Bounded from side to side and proximo- 

 distally, it terminates in a pointed process, which reaches a more distal level than 

 the corresponding process of the tibia, from which it also differs in being narrower 

 and more pointed and being placed in a plane nearer the heel. Proximally, this 

 surface, which is subcutaneous, is continuous with the triangular subcutaneous 

 area so clearly defined by the convergence of the lines which unite to form the 

 anterior crest. The anterior border and tip of the lateral malleolus furnish 

 attachments to the anterior talo-fibular and calcaneo - fibular ligaments. The 

 posterior surface of the lateral malleolus, broad proximally, where it is confluent 

 with the lateral or peroneal surface, is reduced in width distally by the presence 

 of the pit which lies to its medial side. This aspect of the bone is grooved (sulcus 

 malleolaris) by the tendons of the peronseus longus and brevis muscles, which 

 curve round the posterior and distal aspects of the malleolus. 



The proportionate length of the fibula to the body height is as 1 is to 4'37-4'82. 



Arterial Foramina. Numerpus minute vascular canals are seen piercing the lateral surface of 

 the head, and one or two of larger size are seen on the medial surface immediately anterior to the 

 proximal articular facet. The canal for the nutrient artery of the body, which has a distal 

 direction, is situated on the posterior surface of the bone about its middle. The lateral 

 surface of the lateral malleolus displays the openings of many small canals, and one or two larger 

 openings are to be noted at the bottom of the pit behind the distal articular surface. 



Connexions. The head and lateral malleolus, and part of the body immediately proximal to 

 the latter, are subcutaneous. The remainder of the body is covered on all sides by the muscles 

 which surround it. Proximally the bone plays no part in the formation of the knee-joint, but 

 distally it assists materially in strengthening the ankle-joint by its union with the tibia and it; 

 articulation with the talus. In position the bone is not parallel to the axis of the tibia, but 

 oblique to it, its proximal extremity lying posterior and lateral to a vertical line passing through 

 the lateral malleolus. 



Ossification. The body begins to ossify about the middle of the second month of 

 foetal life. At the end of the third month there is but little difference in size between it 

 and the tibia, and at birth the fibula is much larger in proportion to the size of the 



