160 ARTICULATIONS OF THE LOWER LIMB. 



forwards and inwards from the fore part of the outer malleolus to a part of 

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

 of the three. 3. The posterior band, the strongest of the three, passes 

 almost horizontally inwards from the pit on the inner and back part of the 

 malleolus to the posterior surface of the astragalus. 



Fig. 147. TRANSVERSE- VERTICAL SECTION OP THE RIGHT 

 Fig. 147. ANKLE-JOINT NEAR ITS MIDDLE, AND OF THE POSTERIOR 



TALO-CALCANEAL ARTICULATION, so AS TO SHOW THE 

 SHAPE OP THE ARTICULAR SURFACES AND CAVITIES, 

 VIEWED FROM BEFORE. ^ 



1, internal, 2, external malleolus ; 3, placed on the astra- 

 galus at the angle between its superior and its external 

 raalleolar surfaces ; 4, points to the interosseous 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 inter- 

 osseous calcaneo-talar ligament ; 9, great tuberosity of the 

 calcaneum : between the tibia, fibula and astragalus, the 

 synovial cavity is indicated by the dark space enclosed by a 

 white line ; between the astragalus and os calcis a section of 

 the posterior calcaneo-talar synovial cavity is shown. 



The anterior and posterior ligaments are merely 

 scattered fibres in front of and behind the joint ; 

 those of the posterior ligament are weak and 

 principally transverse. 



The synovial membrane of the ankle-joint extends upwards by a small 

 process which lines the inferior peroneo-tibial articulation. 



MOVEMENTS. The movements at the ankle-joint are mainly those of flexion and 

 extension of the foot, and the directions of those movements are principally determined 

 by the shape of the articular surfaces. The external border of the superior cartila- 

 ginous surface of the astragalus is curved, and longer than the internal border, and 

 hence extension of the ankle-joint is accompanied with a slight inward movement 

 of the toes. The horizontal surfaces of both the tibia and astragalus are broader in 

 front than behind ; hence in complete extension of the ankle the narrow part of the 

 astragalus is brought into the widest part of the space between the malleoli, and a 

 certain amount of lateral motion is allowed, whereas in complete flexion, as when the 

 weight of the body, with completely bended knees, is supported on the toes, the broad 

 part of the surface of the astragalus is pushed back into the narrowest part of the 

 space, and the inferior extremity of the fibula is pressed upon, so as to stretch the 

 ligaments between it and the tibia, and give a certain amount of spring to the joint. 

 There appears to be no other movement between the tibia and fibula ; these bones 

 being bound together at their lower ends with remarkable firmness. 



ARTICULATIONS OF THE FOOT. 



ARTICULATIONS OF THE CALCANEUM, ASTRAGALUS, AND SCAPHOID BONES 

 ONE WITH ANOTHER. The astragalus is connected with the calcaneum by two 

 synovial articulations, viz., by a posterior one peculiar to those two bones, 

 and by an anterior one common to them with the scaphoid bone. The fol- 

 lowing are the principal parts requiring description. 



Astragalo-calcaneal ligaments. The interosseous ligament, broad and 

 strong, passes vertically downwards from the groove between the anterior 

 and posterior articular surfaces of the astragalus to the similar groove between 

 the corresponding articular surfaces of the calcaneum. A membranous 

 posterior ligament connects the posterior border of the astragalus with the 

 upper surface of the calcaneam ; its fibres are oblique and very short. 



