THE ANKLE-JOINT. 



19] 



extremity of the fibula, to the external surface of the os calcis. 2. The anterior land 

 passes obliquely forwards and inwards from the fore part of the outer malleolus to 

 the body of the astragalus in front of its external malleolar surface ; it is the shortest 

 of the three. 3. The posterior land, the strongest of the three, passes almost 



Fig. 218. THE LOWER TIBIO-FIBULAR ARTICULATION AND ANKLE- 

 JOINT FROM BEHIND. (Allen Thomson.) \ 



1, interosseous membrane ; 2, posterior ligament of the lower tibio- 

 fibular articulation ; 3, internal lateral ligament of the ankle- joint ; 4, pos- 

 terior, and 5, middle bands of the external lateral ligament of the ankle- 

 joint ; 6, external, and 7, posterior ustragalo-calcaneal ligaments. 



horizontally inwards from the pit on the inner side of the 

 malleolus to the external tubercle of the astragalus, and 

 the surface between the latter and the fibular articular 

 facet. 



The anterior ligament is a thin and lax membrane 

 which passes from the anterior margin of the lower end of 

 the tibia to the upper aspect of the head of the astragalus. 

 Beneath it is a cushion of fat which rests in the hollow of 

 the neck of the astragalus. 



The posterior ligament is fixed to the tibia and astra- 

 galus near their articular surfaces. Its fibres are weak, and 

 run chiefly inwards, radiating from the external malleolus 

 upwards to the tibia and downwards to the astragalus. 



The synovial cavity of the ankle-joint extends upwards for about a quarter of an 

 inch into the lower tibio-fibular articulation. On the outer side of the entrance to 

 this recess the synovial membrane forms a small fold containing fat, which occupies 



Fig. 219. CORONAL SECTION OP THE RIGHT ANKLE-JOINT NEAR ITS 



MIDDLE, AND OF THE POSTERIOR ASTRAGALO-CALCANEAL ARTICULA- 

 TION, VIEWED FROM BEFORE. ( Allen Thomson. ) i 



1. internal, 2, external malleolus ; 3, placed on the astragalus at the 

 angle between its superior and its external surfaces ; 4, inferior interos- 

 seous tibio-fibular ligament ; 5, internal lateral ligament of the ankle- 

 joint ; 6, sustentaculum tali ; 7, calcaneo-fibular or middle part of the 

 external lateral ligament ; 8. inner part of the interosseous astragalo-cal- 

 caneal ligament ; 9, tuberosity of the calcaneurn. 



the angular interval between the three bones, and is carried 

 upwards between the tibia and fibula when the external 

 malleolus is forced outwards in flexion of the ankle-joint. At 

 the front and back of the joint are larger synovial folds 

 projecting between the tibia and astragalus. 



Movements, &c. The movements of the ankle-joint are flexion, in which the toes are raised 

 towards the leg 1 , and extension, in which the toes are depressed and the foot brought into the line 

 of the leg 1 . The whole range of movement does not exceed 90. Although the horizontal surfaces 

 of both the tibia and astragalus are broader in front than behind, the malleoli are in contact 

 with the sides of the astragalus in all positions of the joint, a slight degree of lateral move- 

 ment of the external malleolus being permitted by the inferior tibio-fibular ligaments and the 

 elasticity of the shaft of the fibula. When the joint is bent the wide part of the astragalus is 

 pushed back into the socket, and the external malleolus is forced outwards ; whereas in 

 extension the external malleolus follows the curve of the outer surface of the astragalus, 

 being drawn inwards mainly by the posterior band of the external lateral ligament. In this 

 way a certain amount of spring is given to the articulation. In the mid-position of the joint,. 



