The Fibula is a long, slender bone on the outer side of the leg. It articulates above with the outer tuberosity of the tibia, and below with the lower end of the tibia and the outer surface of the astragalus.

Pig. 15. - Tibia and Fibula (Posterior Surfaces).

The Upper Extremity is irregularly rounded, and has on its internal surface a facet for articulation with the tibia, and just above this is a pointed process-the styloid process.

The Shaft is very irregular in shape and twisted on itself, but a very narrow anterior surface can be distinguished between the interosseous and external borders. The external border splits below to form a triangular subcutaneous area on the outer malleolus, and behind this line is the external surface. The surface next the external surface is the posterior surface, which is divided by a sharp ridge. (This ridge may be mistaken for the interosseous ridge, but that can be determined by following up the line from the triangular surface on the malleolus. This line is the external border of the anterior surface.)

The Lower Extremity is flattened and expanded to form the external malleolus, on the internal surface of which is the facet for articulation with the outer surface of the astragalus. Just behind this facet is the digital fossa for the insertion of a ligament.

Ossification is similar to that of the tibia, except that the centre for the shaft is the only one that appears before birth.