The fibula is of irregularly triangular shape, and presents three surfaces, and three borders. To the inner border, or ridge, is attached the interosseous membrane, the fibres of which pursue a precisely analogous direction with the fibres of the interosseous membrane in the forearm; i. e., they pass obliquely downwards from the tibia to the fibula, from within outwards. The surfaces, to which the muscles which act upon the foot are attached, correspond but imperfectly with the surfaces upon the ulna, yet the fibula can hardly be regarded as twisted upon itself, as stated by Meckel. The external malleolus looks inwards, as does the styloid process of the ulna, and maintains its proper relative position with the eminences upon the head of the bone.