486 SURGICAL APPLIED ANATOMY. [Chap. xxm. 



an oblique direction from above downwards and in- 

 wards. The foot therefore tends to become abducted, 

 a tendency resisted by such powerful ligaments as the 

 internal lateral of the ankle and those connecting the 

 os calcis with the astragalus. In flat-foot these liga- 

 ments yield, and the toes consequently are turned out 

 or abducted. The ligament, however, that is mainly 

 affected in this deformity is the inferior calcaneo- 

 scaphoid. This strong band of fibres supports the 

 head of the astragalus and holds up the very key- 

 stone of the plantar arch. When it yields, the head 

 of the astragalus is pressed forwards, downwards, 

 and inwards by the superincumbent weight, and the 

 foot beyond becomes, as a consequence, over-extended 

 and rotated out. The long and short plantar liga- 

 ments also, which contribute so much to the main- 

 tenance of the arch of the foot, in time yield, and 

 allow of a still greater degree of deformity. In 

 neglected cases the distortion is rendered more or less 

 permanent by alterations in the shape of the tarsal 

 bones, and by a contraction of such ligaments as have 

 been relaxed by the deformity. The foot being 

 abducted, and its outer border a little raised, the 

 peronei muscles become relaxed, subsequently shorten 

 and contract, and so contribute to the permanency of 

 the disorder. It will be understood that the abnormal 

 pressure brought to bear upon the various tarsal 

 bones and articulations will cause severe pain to be 

 often associated with this affection. 



It may be noted that the medio-tarsal joint, which 

 is so conspicuously involved in the distortion, is 

 supplied by the anterior tibial, musculo-cutaneous, 

 and external plantar nerves. 



According to Duchenne (of Boulogne), flat-foot is 

 rather a muscular affection in the first instance, and 

 is due to a weakening of the peroneus longus, the 

 sinking of the plantar arch being subsequent thereto. 



