THE FOOT 159 



Peroneus longus. Extensor longus digitorum. 



Peroneus brevis. Extensor proprius hallucis. 



The fibula affords insertion to the biceps. 



The following ligaments are connected with it : — 



External lateral of the knee. Transverse. 



Anterior tibio-fibular. Anterior tibio-fibular (inferior). 



Posterior tibio-fibular. Posterior tibio-fibular. 



Interosseous membrane. External annular. 



External lateral ligament of ankle. Anterior annular (vertical). 



Blood-supply. — The fibula receives the nutrient artery of its shaft from the 

 peroneal Ijranch of the posterior tibial. The head is nourished by branches from 

 the inferior external articular branch of the pophteal artery, and the malleolus is 

 supplied mainly by the peroneal, anterior peroneal, and external malleolar arteries. 



Ossification. — The shaft of the fibula commences to ossify in the eighth week 

 of intra-uterine life. A nucleus appears for the lower in the second year, and one 

 in the fifth year for the upper extremity. The lower extremity fuses with the shaft 

 about twenty, but the upper one remains separate until the twenty-second year. 



The human fibula differs from all others in the excessive length of its malleolus; 

 in no other vertebrate does this process descend below the level of the tibial malle- 

 olus. In the majority of mammals the tibial descends to a lower level than the 

 fibular malleolus. In the human embryo of the fourth month, the outer (fibular) 

 is very much smaller than the inner (tibial) malleolus. At the seventh month 

 they are equal in length; at birth, the fibular malleolus is the longer; and by the 

 second year it assumes its adult proportion. (Gegenbaur. ) 



The fibula is a vestigial bone in man, and survdves mainly on account of the 

 excessive development of its malleolus. This accounts for the fact that the loAver 

 epiphysis, though appearing first, unites with the shaft before the upper epiphysis. 

 In birds, the head of the bone is large, and enters into the formation of the knee- 

 joint, whilst the lower end atrophies. 



THE FOOT 



The bones comprised in the skeleton of the foot are arranged in three groups: — 

 tarsus, metatarsus, and phalanges. 



The tarsus consists of seven l)ones: — The astragalus, os calcis or calcaneum, 

 scaphoid, cuboid, and three cuneiform bones. 



THE ASTRAGALUS 



This bone may, for descriptive purposes, be divided into a body, neck, and 

 head. The body is quadrilateral. Its upper aspect resembles a segment of the 

 wheel of a pulley; hence it is called the trochlear surface. It is broader in front 

 than ])ehind, and articulates with the lower end of the tibia. 



The inferior surface is occupied by an elongated concave facet for articulation 

 with the calcaneum. 



The internal surface presents a pyriform facet, broad in front, and continuous 

 with the trochlea: it articulates with the tibial malleolus. Below this facet, the 

 inner surface is rough for the attachment of the deep fibres of the deltoid ligament. 



The external surface is almost entirely occupied by a triangular concave facet, 

 broad above where it is continuous with the trochlea, for articulation with the 

 fibular malleolus. 



