SURGICAL ANATOMY OF THE FOOT. 213 



the heads of the metatarsal bones anteriorly. The weakest part of the arch is the 

 joint between the astragalus and scaphoid, and here it is more liable to yield in 

 those who are overweighted, and in those in whom the ligaments which complete 

 and preserve the arch are relaxed. This weak point in the arch is braced on its 

 concave surface by the inferior calcaneo-navicular ligament, which is more elastic 

 than most other ligaments, and thus allows the arch to yield from jars or shocks 

 applied to the anterior portion of the foot and quickly restores it to its pristine con- 

 dition. This ligament is supported internally by blending with the Deltoid ligament, 

 and inferiorly by the tendon of the Tibialis posticus muscle, which is spread out 

 into a fan-shaped insertion, and prevents undue tension of the ligament or such an 

 amount of stretching as would permanently elongate it. 



In addition to this longitudinal arch the foot presents a transverse arch, at the 

 anterior part of the tarsus and hinder part of the metatarsus. This, however, can 

 scarcely be described as a true arch, but presents more the character of a half-dome. 

 The inner border of the central portion of the longitudinal arch is elevated from 

 the ground, and from this point the bones arch over to the outer border, which is 

 in contact with the ground, and, assisted by the longitudinal arch, produce a sort of 

 rounded niche on the inner side of the foot, which gives the appearance of a 

 transverse as well as a longitudinal arch. 



The line of the foot, from the point of the heel to the toes, is not quite straight, 

 but is directed a little outward, so that the inner border is a little convex and the 

 outer border concave. This disposition of the bones becomes more marked when 

 the longitudinal arch of the foot is lost, as in the disease known under the name 

 of "flat-foot." 



Surface Form. On the dorsum of the foot the individual bones are not to be distinguished 

 with the exception of the head of the astragalus, which forms a rounded projection in front of 

 the ankle-joint when the foot is forcibly extended. The whole surface forms a smooth convex 

 outline, the summit of which is the ridge formed by the head of the astragalus, the navicular, 

 the middle cuneiform, and the second metatarsal bones ; from this it gradually inclines outward 

 and more rapidly inward. On the inner side of the foot, the internal tuberosity of the os calcis 

 and the ridge separating the inner from the posterior surface of the bone may be felt most pos- 

 teriorly. In front of this, and below the internal malleolus, may be felt the projection of the 

 sustentaculum tali. Passing forward is the well-marked tuberosity of the navicular bone, situ- 

 ated about an inch or an inch and a quarter in front of the internal malleolus. Further toward 

 the front, the ridge formed by the base of the first metatarsal bone can be obscurely felt, and 

 from this the shaft of the bone can be traced to the expanded head articulating with the base 

 of the first phalanx of the great toe. Immediately beneath the base of this phalanx, the 

 internal sesamoid bone is to be felt. Lastly, the expanded ends of the bones forming the last 

 joint of the great toe are to be felt. On the outer side of the foot the most posterior bony 

 point is the outer tuberosity of the os calcis, with the ridge separating the , posterior from the 

 outer surface of the bone. In front of this the greater part of the external surface of the os 

 calcis is subcutaneous ; on it, below and in front of the external malleolus, may be felt the pero- 

 neal ridge, when this process is present. Farther forward, the base of the fifth metatarsal bone 

 forms a prominent and well-defined landmark, and in front of this the shaft of the bone, with 

 its expanded head, and the base of the first phalanx may be defined. The sole of the foot is 

 almost entirely covered by soft parts, so that but lew bony parts are to be made out, and these 

 somewhat obscurely. The hinder part of the under surface of the os calcis and the heads of the 

 metatarsal bones, with the exception of the first, which is concealed by the sesamoid bones, 

 may be recognized. 



Surgical Anatomy. Considering the injuries to which the foot is subjected, it is surpris- 

 ing how seldom the tarsal bones are fractured. This is no doubt due to the fact that the tarsus 

 is composed of a number of bones, articulated by a considerable extent of surface and joined 

 together by very strong ligaments, which serve to break the force of violence applied to this 

 part of the body. When fracture does occur, these bones, being composed for the most part 

 of a soft cancellous structure, covered only by a thin shell of compact tissue, are often extensively 

 comminuted, especially as most of the fractures are produced by direct violence. And having 

 only a very scanty amount of soft parts over them, the fractures are very often compound, and 

 amputation is frequently necessary. 



When fracture occurs in the anterior group of tarsal bones, it is almost invariably the result 

 of direct violence ; but fractures of the posterior group, that is, of the calcaneum and astrag- 

 alus, are most frequently produced by falls from a height on to the feet ; though fracture of 

 the os calcis may be caused by direct violence or by muscular action. The posterior part of the 

 bone, that is, the part behind the articular surfaces, is almost always the seat of the fracture, 

 though some few cases of fracture of the sustentaculum tali and of vertical fracture between 

 the two articulating facets have been recorded, The neck of the astragalus, being the weakest 



