530 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 turned out. The os calcis slants inwards and its 

 anterior end is depressed. The sustentaculum tali, 

 the head of the astragalus, and the scaphoid tubercle 

 form prominences on the inner side of the foot. The 

 long and short plantar ligaments also, which contri- 

 bute so much to the maintenance of the arch of the 

 foot, in time yield, and allow of a still greater 

 degree of deformity. There is a stretching also 

 of the deltoid ligament. 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 be- 

 come relaxed, shorten, and contribute to the per- 

 manency 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, inusculo-cutaneous, 

 and external plantar nerves. 



