LIGAMENTS OF ANKLE-JOINT. 643 



The external is divided into three separate pieces ; and to find these the 

 peronei muscles, and the remains of the annular ligament below the outer 

 malleolus, should be taken away. 



The anterior or tibio-tarsal ligament is a thin fibrous membrane, which 

 is attached to the tibia close to the articular surface ; and to the upper part 

 of the astragalus near the articulation with the scaphoid bone. In the 

 ligament are some rounded intervals and apertures for vessels. On the 

 sides it joins the lateral ligaments. 



The posterior ligament is thinner internally than externally ; and it is 

 inserted into the tibia and the astragalus, close to the articular surfaces of 

 the bones. Towards the outer part it consists of transverse fibres, which 

 are fixed into the hollow on the inner surface of the external malleolus. 



The internal lateral or deltoid ligament (fig. 221) is attached by its 

 upper or pointed part to the inner malleolus, and by its base to the astraga- 

 lus, the os calcis, and the scaphoid bone, by fibres which radiate to their 

 insertion in this manner : The posterior (*) are directed to the hinder part 

 of the inner surface of the astragalus ; the middle ( 2 ) pass vertically to the 

 sustentaculum tali of the os calcis ; and the anterior (*), which are thin and 

 oblique, join the inferior calcaneo-scaphoid ligament and the inner side of 

 the scaphoid bone. The tendons of the tibialis posticus and flexor longus 

 digitorum are in contact with this ligament. 



The external lateral ligament (fig. 222) consists of three separate pieces, 

 anterior, middle, and posterior, which are attached to the astragalus and 

 the os calcis. The anterior piece (*) is a short flat band, which is directed 

 from the fore part of the malleolus to the side of the astragalus in front of 

 the lateral articular surface. The middle portion ( 3 ) is flattened and de- 

 scends from the tip of the malleolus to the outer surface of the os calcis, 

 about the middle. The posterior ( 2 ) is the strongest, and is almost hori- 

 zontal in direction ; it is connected externally to the pit on the inner sur- 

 face of the malleolus, and is inserted into the posterior part of the astraga- 

 lus behind the upper articular surface, extending to the groove for the flexor 

 pollicis tendon. 



The posterior and middle fasciculi are placed beneath the peronei mus- 

 cles. The middle part is but slightly in contact above with the synovial 

 membrane of the ankle joint ; and both it and the posterior piece touch 

 the synovial membrane between the astragalus and the os calcis. 



Dissection. Dividing the ligaments of the ankle joint, separate the as- 

 tragalus from the bones of the leg, to see the osseous surfaces entering into 

 the joint. 



The synovial membrane of the joint lines the capsule, and is simple in 

 its arrangement. 



Articular surfaces. On the tibia there are two articular faces, one of 

 which corresponds with the end of the shaft, and the other with the mal- 

 leolus. On the fibula the surface of the malleolus which is turned to the 

 astragalus is tipped with cartilage. 



The astragalus has a central articular surface, wider before than behind 

 and trochlear-shaped, which touches the end of the tibia : and on its sides 

 are articular impressions for contact with the malleoli, but the outer one is 

 the largest. 



Movement. Only the movements of flexion and extension are permitted 

 in the ankle : in the former state the toes are raised towards the fore part 

 of the leg ; and in the latter, they are pointed towards the ground. 



Inflexion the astragalus moves backwards so as to project behind ; and 



