158 THE SKELETON 



THE FIBULA 



This is a long slender l)one lying postero-externally in the leg, to the outer side of 

 and somewhat i)osteri()r to the tibia, with which it articulates both above and below. 

 It is excluded from the knee-joint but forms the outer boundary of the ankle-joint. 



The upper extremity, or head, is a rounded prominence. Its u])per surface is 

 rough externally for the attachment of the biceps tendon and the long external 

 lateral ligament of the knee-joint; internally it presents a round or oval articular 

 facet for the outer tuberosity of the tibia; the margins of this facet give attachment to 

 the capsular ligament of the superior tibio-fibular articulation. Posteriorly, it rises 

 into a pointed process, the styloid process, which gives attachment at its apex to 

 the short external lateral ligament of the knee and laterally to part of the biceps 

 tendon. The posterior aspect of the head gives attachment to the soleus, the outer 

 to the peroneus longus, the anterior to the extemor longus digitorum, and the inner 

 lies adjacent to the tibia. 



The lower extremity, external malleolus, is a triangular piece of bone placed 

 with the base uppermost. Its outer surface is convex and subcutaneous. The inner 

 surface is divided into an anterior and upper area, triangular in outline and convex 

 from above downwards for articulation with the outer side of the astragalus, and a 

 lower and posterior excavated area, the digital fossa, in Avhich are attached the 

 transverse inferior tibio-fibular ligament and the posterior band of the external 

 lateral ligament of the ankle. The anterior border is rough; it gives attachment to 

 the anterior band of the external lateral ligament of the ankle, the anterior inferior 

 tibio-tibular ligament, and the anterior annular ligament. The posterior border is 

 grooved for the peronei tendons, and the apex gives attachment to the middle band 

 of the external lateral ligament of the ankle. 



The shaft is quadrangular, possessing four borders and surfaces. The antero- 

 external border commences in front of the head and terminates lielow by dividing to 

 enclose the subcutaneous surface on the outer side of the external malleolus. The 

 antero-internal border also commences in front of the head, close to the antero- 

 extt'rnal liorder; it terminates below by dividing to enclose a rough triangular 

 area innuediately above the facet for the astragalus; this area gives attachment 

 to the inferior interosseous ligament, and sometimes bears at its lower end a 

 narrow facet for the tibia. The postero-internal border commences at the inner 

 side of the head and terminates below by joining the antero-internal border at the 

 upper part of the lower fourth of the shaft. The postero-external border runs from 

 the back of the head to the inner border of the peroneal groove on the back of the 

 lower extremity; it gives attachment to the fascia separating the peronei and the 

 flexor muscles. 



The anterior or extensor surface between the antero-internal and antero-external 

 l)()rders is narrow above but broader below; three muscles spring from it: externally 

 in the ui)i)('r two-thirds the extensor longus digitorum, and in the lower third the 

 j,n-n,irtis tcrfiiis; internally in the middle third the extensor longus haUiicis. The 

 internal surface l)etween the antero- and postero-internal borders is usuallv concave; 

 it Ls narrow al)ov(; and below, and broadest in the middle; it is frequently crossed 

 l)y on(> or more o])li(iue ridges, and it gives attachment to the <t6/a//./ ^)ox;wrs. 

 The posterior surface between the postero-internal and external l^orders is twisted; 

 it looks Ijackwards al>ove and inwards below; in its upper third it gives attach- 

 ment to the soleiis and in the lower two-thirds to the flexor longus hallucis. The 

 external surface ])etween the antej-o- and postero-external borders is also twisted, 

 looking outwards abo\c and backwards below, where it is continuous with the 

 groove on the peronei tendons; it gives attachment in its upper two-thirds to the 

 pernnens longus and in the lower two-thirds to the peroneiix brevis. 



The muscles arising from the libula are: — 



Soleus. Peroneus tertius. 



Tibialis i)osticus. Flexor longus hallucis. 



