268 



THE ARTICI 7. A TWXS 



to a. tubercle on the middle of the out«r surface of the calcaneum. The posterior 

 fasciculus is almost horizontal; it is a strong, thick l)and attached at one end to 

 the i)osterior border of the malleolus, and slightly to the fossa on the internal 

 surface; and at the other end to the astragalus, behind the articular facet for the 

 fibula, as well as to a tubercle on the outer side of the groove for the flexor lonyus 

 hallucis. The middle fasciculus is covered by the tendons of the peronei longus and 

 bren's ; and in extension, the posterior fasciculus is received into the pit on the 

 inner surface of the external malleolus. 



The synovial membrane is very extensive. Besides lining the ligaments of 

 the ankle, it extends upwards between the tibia and fibula, forming a short cul-de- 

 sac as far as the interosseous ligament. Upon the anterior and posterior ligaments 

 it is very loose, and extends beyond the limits of the articulation. It is said to 

 contain more synovia than any other joint. 



Fig. 254. — Ligaments seen from the Back of the Ankle-joint. 



Posterior ligament of ankle- 

 joint 



Posterior part of the internal 

 lateral ligament 



The lower part of the inter- 

 osseous membrane 



Transverse ligament of inferior 

 tibio-flbular joint 



Posterior fasciculus of external 

 lateral ligament 



Middle fasciculus of external 

 lateral ligament 



The nerve-supply is from the internal saphenous, posterior tilnal, and the 

 external division of the anterior tilnal. 



The arterial supply comes from the anterior tibial, the anterior peroneal, the 

 external malleolar, the posterior tibial, and posterior peroneal. 



Movements.— Tliis being a true hinge Joint, flexion and extension are the only 

 movements of which it is capable, there being no lateral motion, except in extreme 

 extension, when the narrowest part of the astragalus is thrust forwards into the 

 widest part of the tibio-fibular arch. In flexion the astragalus is tightly embraced 

 l)y the malleoli, and lateral movement is impossible. Flexion is limited by: (i) 

 nearly tbe whole of the fibres of the internal lateral ligament, none but the most 

 anterior being relaxed; (ii) the jjosterior and middle portions of the external lateral 

 ligament, especially th^ })osterior; (iii) the ])osterior ligament of the ankle. It is 

 also limited by the neck of the astragalus abutting on the edge of the tibia. 

 Extension is limited by: (i) the anterior fibres of the internal lateral ligament; 

 (ii) the anterior and middle portions of tlie external lateral ligament; (iii) the 



