FIBULA. 93 



FIBULA. The fibula is a long and slender prismoid bone, divisible 

 into a shaft and two extremities. 



The superior extremity or head is thick and large, and depressed 

 upon the upper part by a concave surface, which articulates with 

 the external tuberosity of the tibia. Externally to this surface is 

 a thick and rough prominence, for the attachment of the external 

 lateral ligaments of the knee-joint, terminated behind by a styloid 

 process, for the insertion of the tendon of the biceps. 



The lower extremity is flattened from without inwards, and pro- 

 longed downwards beyond the articular surface of the tibia, form- 

 ing the external malleolus. Its external side presents a rough and 

 triangular -surface, which is subcutaneous. Upon the internal surface 

 is a smooth triangular facet, to articulate with the astragalus; 

 and a rough depression, for the attachment of the interosseous 

 ligament. The anterior border is thin and sharp ; and the posterior, 

 broad and grooved, for the tendons of the peronei muscles. 



To place the bone in its proper position, and ascertain to which 

 leg it belongs, let the inferior or flattened extremity be directed 

 downwards, and the narrow border of the malleolus forwards ; the 

 triangular subcutaneous surface will then point to the side corre- 

 sponding with the limb of which the bone forms a part. 



The shaft of the fibula is prismoid, and presents three surfaces ; 

 external, internal, and posterior ; and three borders. The external 

 surface is the broadest of the three ; it commences upon the anterior 

 part of the bone above, and curves around it so as to terminate 

 upon its posterior side below. The surface is completely occupied 

 by the two peronei muscles. The internal surface commences on 

 the side of the superior articular surface, and terminates below, by 

 narrowing to a ridge, which is continuous with the anterior border 

 of the malleolus. It is marked along its middle by the interosseous 

 ridge, which is lost above and below in the inner border of the bone. 



The posterior surface is twisted like the external, it commences 

 above on the posterior side of the bone, and terminates below on its 

 internal side ; at about its middle is the nutritious for amen, which is 

 directed downwards. 



The internal border commences superiorly in common with the 

 interosseous ridge, and bifurcates inferiorly into two lines, which 

 bound the triangular subcutaneous space of the external malleolus. 

 The external border begins at the base of the styloid process upon the 

 head of the fibula, and winds around the bone, following the direc- 

 tion of the corresponding surface. The posterior border is sharp and 

 prominent, and is lost inferiorly in the interosseous ridge. 



Developement. By three centres ; one for the shaft, and one for 

 each extremity. 



Articulations. With the tibia and astragalus. 



Attachment of Muscles. To nine; by the head, to the tendon of the 

 biceps and soleus ; by the shaft, its external surface, to the 

 peroneous longusandbrevis; internal surface, to the extensor longus 

 digitorum, extensor proprius pollicis, peroneus tertius, and tibialis 



