440 . HUMAN ANATOMY. 



the capsule. The anteriof band^ (Fig- 457) passes forward and inward from the 

 front border of the malleolus to the astragalus in front of the lateral articular surface. 

 It is made tense in plantar flexion. 'Ws.^ posterior band'' (Fig. 457) — a very strong 

 one — arises from the hollow on the inside of the tip of the outer malleolus and runs 

 inward and backward to the astragalus behind the posterior outer angle of the 

 articular surface. It is made tense in dorsal flexion. With the transverse tibio- 

 fibular ligament it considerably strengthens the back of the capsule. The middle 

 band^ (Fig. 457), more superficial and tending to be free from the capsule, runs down- 

 ward and backward to a faint tubercle on the outer side of the calcaneum. It can 

 be made fully tense by no motion in the ankle-joint alone, but restrains certain 

 motions of the astragalus on the calcaneum. The capsule between these bands is 

 excessively thin. 



The synovial membrane lining the capsule is in the main perfectly simple, 

 following the latter ; it presents, however, a prominent fold on the inside of the 

 joint over the posterior band of the external lateral ligament, and makes something 

 of a pouch above this, below the transverse ligament. It covers the pad of fat be- 

 tween the bones of the leg. 



Movements. — The articulation at the ankle is essentially a hinge-joint, although 

 not a pure one, since the fibula moves on the tibia, and the astragalus, being more 

 closely fastened to the fibula, follows the latter in its movements ; thus, the outer 

 end of the transverse axis of rotation is subject to displacement. When the foot is 

 midway between flexion and extension, it is possible in the dead body to impart a 

 certain lateral motion to the astragalus, the lateral ligaments being apparently not 

 tense ; but it is highly improbable that this ever occurs during life, unless under 

 accidental circumstances, for the muscles supplement the ligaments. As the foot 

 moves into dorsal flexion the broadest part of the astragalus comes into the broadest 

 part of the socket, forcing the malleoli somewhat apart. In some cases it would 

 appear that the fibula rotates on a longitudinal axis, while the head slips backward, 

 but both the degree and even the nature of the movement are uncertain. The foot 

 is held firm and immovable by the spring of the bones, by the tension of the pos- 

 terior ligament and of the posterior and middle divisions of the external lateral one, 

 and especially by the strong posterior part of the internal lateral. In extreme 

 plantar flexion the narrowest part of the astragalus is in the socket, of which the 

 bones are in the greatest possible approximation, so that the pad of fat between 

 them is squeezed into the joint and rests against the sickle-shaped facet of the 

 superior surface, except that the hind end of the latter is against the posterior tibio- 

 fibular ligament. The fold in the posterior ligament is brought against the back of 

 the bone. The anterior ligament and the anterior parts of the lateral ones are tense. 

 Further support is gained by the back of the astragalus below the articular facet 

 resting against the back of the tibia so as to lock the joint. The front bands of both 

 outer and inner lateral ligaments are tense. The action of the numerous muscles 

 crossing the ankle is, of course, greatly to strengthen it and to prevent any giving 

 between the bones when the ligaments are not stretched to the utmost. Moreover, 

 the elastici«"y of the fibula is an important element in the mechanics of the ankle- 

 joint, and one that makes it impossible to contrive a model that will represent the 

 conditions actually existing. 



THE ARTICULATIONS OF THE FOOT. 



As has been shown, the bones of the foot are so arranged (Fig. 431) that the 

 astragalus, placed on the calcaneum, carries with it the three inner toes, while the two 

 outer, resting on the cuboid, are more under the influence of the movements of the 

 calcaneum. It is, however, possible for the scaphoid and cuboid to move together 

 on the two proximal bones. The essential joints for the movements of the foot, 

 besides the ankle-joint, are those between the calcaneum and astragahis and those 

 between the astragalus and scaphoid and the calca7ieum and cuboid respectively. 

 The joints between the smaller bones at the front of the tarsus are mechanically un- 

 important, being chiefly to break shocks and to allow an indefinite giving in the 

 arch of the foot. As certain ligaments are concerned in the protection of several 



* Lig. talofibulare aaterius. 'Lie. talofibalare posterins. ^ Lig. calcaneolibulare. 



