THE FOOT AS A WHOLE. 



449 



The weight-bearing 

 Fig. 466. 



removing the first and fifth metatarsals with their phalanges and the first cuneiform 

 bone, without impairing the stability of the foot. The fourth metatarsal may next be 

 taken away without trouble. If the second with its cuneiform be detached with care, 

 the arch is still reasonably firm. It is possible to preserve the arch after taking out 

 the astragalus, and then removing the scaphoid. Although the arch still stands, it 

 will bear little weight, the third cuneiform being inadequately supported behind ; but 

 with the scaphoid and astragalus retained the arch is a good one. The arches 

 depend very much for their stability on the action of the peroneus longus and the 

 tibialis posticus, which pull against each other from opposite sides. The former is 

 efficient in maintaining the transverse arch, the latter in maintaining both the trans- 

 verse and the antero-posterior. To these should be added the plantar fascia and 

 the muscles to the toes arising from the calcaneum. When in life the weight is 

 equally divided between the feet, the part in contact with the ground is the heel, the 

 outer border of the foot, the region of the heads of the metatarsals, and, separated 

 from the rest, the balls of the toes, which bear no weight. The outer border also, as 

 a rule, is doing no work and often does not even touch the ground, It is easy to 

 pass a thin spatula under the head of the fifth metatarsal, and usually not hard to 

 pass it under that of the first, thus showing that in this position they are not essential 

 parts of tli^ arch. When the whole or nearly the whole weight is transferred to 

 one foot the following changes occur. The head of the astragalus turns inward, at 

 the same time sinking under the weight of the body so as to make a prominence at 

 the inner side of the foot. The internal malleolus follows this movement. The 

 outer malleolus advances, but does not descend. Thus the relation of the front part 

 of the foot to the posterior is one of abduction and eversion 

 region changes both its shape and position. The line at the 

 outer part of the heel is the only part that remains stationary. 

 The surface of pressure (Fig. 466) is broader at the heel and 

 still more so at the heads of the metatarsals. The connecting 

 strip moves inward, but becomes no broader ; sometimes it 

 even narrows. The chief agent in resisting this change, 

 which is greater after fatigue, is the tibialis posticus, which 

 opposes the inner turn of the head of the astragalus which 

 precedes its descent. When this is inadequate, the change 

 of position is exaggerated and the foot breaks down. 



As the heel is raised, under normal conditions, the 

 weight is transmitted through the astragalus chiefly to the 

 bones and soft parts forming the socket for its head, the 

 calcaneum receiving little of it. The strain comes chiefly 

 on the ligaments securing the scaphoid, for that bone is most 

 directly in the line of pressure, which it transmits through 

 the front of the tarsus to the heads of the metatarsals, chiefly 

 to the first ; but in this last respect individuals vary. Usu- 

 ally the region of the heads of the metatarsals narrows, the 

 weight being borne chiefly at the inner side, but in some 

 cases by all the heads. When the weight is borne by the 

 toes, the foot being inverted and abducted, the locking by 

 the catching of the plantar tubercle of the cuboid in the os calcis is an important 

 factor of stability. 



Surface Anatomy. — The malleoli are easily felt, the inner being square, the 

 outer longer and more pointed ; the latter is the lower and the more posterior. The 

 ankle-joint is, therefore, more easily opened from the inner side. The front lower 

 border of the tibia is hard to examine on account of the extensor tendons ; the line 

 of the joint is from one to two centimetres above the tip of the inner malleolus, run- 

 ning transversely. The general features of the os calcis can be made out. The sus- 

 tentaculum is distinct and the peroneal spine can be recognized. Along the inner 

 side, the head of the astragalus can be felt at the dorsum where it enters the hollow 

 of the scaphoid. The tubercle of the latter is lower down and farther forward. The 



Surface of pressure on 

 sole of foot as seen through 

 a glass plate supporting the 

 body. 



^ Lovett : New York Medical Journal, 1896. 

 29 



