_Progress._—There can be little doubt that the natural tendency of the complaint is to subside under the mechanical influence of ordinary exercise, and hence, although the deformity is fairly common in youth, it is rarely found in fully developed adults, except where the distal joint is affected. In one case of this kind the contraction began about puberty, and was still present at the age of fifty-two, but the defect never interfered materially with locomotion. It is possible that some of the ordinary cases terminate, as suggested by Mr. Davies-Colley, by conversion into hallux valgus, but my inquiries have failed to confirm this. _Pathology._—The origin of the condition may be explained in the same manner as that of hammer finger and hammer toe. There is a physiological variation in the range of movement permitted in the articulations of the great toe similar to that demonstrated in the fingers and lesser toes, and in examining a number of healthy feet it will be found that the position of extreme super-extension at the metatarso-phalangeal joint may lie at any point between 30° and 110° beyond the prolonged axis of the metatarsal bone; but if the movement of extension be checked at less than 30°, the symptoms of hallux flexus supervene. The chief distinctive feature in the anatomy of the joint lies in the substitution of two sesamoid bones, with their tendons and connecting tissue, for the glenoid plate developed in all the other articulations, and it is those structures that receive the distal attachment of the plantar fibres of the lateral ligaments. (Figs. 12 and 13.) The function of the lateral ligaments, however, remains the same as in the other toes, and the range of the movement of extension is governed by the development of their plantar fibres. [Illustration: FIG. 12. Bones and ligaments in hallux flexus. 1. Lateral ligament of metatarso-phalangeal joint; inferior fibres attached to sesamoid bone; 2. Lateral ligament of inter-phalangeal joint; inferior fibres blending with glenoid plate.] [Illustration: FIG. 13. Hallux flexus of the distal joint.]