It is met with in rapidly growing children or adolescents of feeble muscular development and with long narrow feet, and those especially who, after leaving school, begin some occupation which entails much standing--such as that of a factory hand, message boy, or domestic servant. To enable him to stand with the least effort for long periods, the patient adopts an attitude which makes little demand on the muscles, and throws nearly all the strain of the body weight on the ligaments and bones of the feet. This, which has been called "the attitude of rest," consists in standing with the limbs apart, the knees slightly flexed, the legs slightly rotated laterally at the knee, and the feet pronated, with the toes pointing laterally. The most important local factors predisposing to flat-foot are weakness of those muscles which normally support the ankle and the tarsal arches, especially the tibiales; weakness of the ligaments of the foot; and softness of the tarsal bones. When these conditions are present and a faulty method of standing and walking is adopted, the undue strain to which the tendons and ligaments are exposed results in their being stretched; the bones are altered in position, and flat-foot results. The head of the talus is displaced medially, and is protruded between the calcaneus and navicular, tending to separate them from one another, stretching the inferior calcaneo-navicular ligament and causing the anterior part of the foot to be abducted. The plantar ligaments--especially the inferior calcaneo-navicular--are stretched and lengthened. In something like 80 per cent. there is the combined deformity--pes plano-valgus--in those who apply for treatment. [Illustration: FIG. 153.--Flat-foot, showing loss of arch.] _Clinical Features._--The patient complains of being easily tired, and of pain in the foot after walking or standing. There is generally more pain before the appearance of the deformity than when it has developed, and at this stage it is not so easily recognised, and is apt to be called "rheumatism." The most common seat of pain is at the medial border of the foot behind the tubercle of the navicular, and this is due to stretching of the inferior calcaneo-navicular ligament. Pain is also complained of in the middle of the dorsum across the instep, from stretching of the interosseous ligaments. Later, there is pain over the greater process of the calcaneus in front of the lateral malleolus, from these bones coming into contact. There may be nocturnal cramp in the muscles of the leg and foot.