266 



THE ARTICrLATTOXS 



the articular facet for the astrao;ahis. It then incHncs a little forwards and down- 

 wards;, to be attaehed to the internal surface of the external malleolus, just above 

 the fossa, and the upper part of the fossa itself. 



The synovial membrane is continuous with that of the ankle-joint; it projects 

 upwards between the bones beyond their articular facets as high as the inferior 

 interosseous liijament. 



The nerve-supply is the same as that of the ankle-joint; the arterial supply 

 is from the peroneal and the anterior peroneal, and sometimes from the anterior 

 tibial, or its external malleolar liranch. 



Tlie movement i)ermitted at this joint is a mere gliding, chiefly in an upward 

 ami downward direction, of the tibula on the tibia. The bones are firmly braced 

 together and yet form a slightly yielding arch, thus allowing a slight lateral 

 expansion during extreme flexion, when the broad part of the astragalus is brought 

 under the arch, by the upward gliding of the fibula on the tibia. To this end the 

 direction of the fibres of the superior and inferior tibio-fibular ligaments is down- 

 wards from tibia to fibula. This mechanical arrangement secures perfect contact 

 of the articular surfaces of the ankle-joint in all positions of the foot. 



4. THE ANKLE-JOINT 

 Class, — Diarthrosis. Subdivision. 



-Ginglymus. 



The ankle is a perfect ginglymus or hinge joint. The bones which enter into 

 its formation are: the lower extremity and internal malleolus of the tibia, and 

 the external malleolus of the fibula, above; and the upper and lateral articular 

 surfaces of the astragalus below. The ligaments uniting the bones are: — 



Anterior. 

 Posterior. 



Internal lateral. 

 External lateral. 



Fig. 252 B. — Right Ankle-joint, showing the Ligaments. 

 (From dissection Viy Mr. W. Pearson, of the Royal College of Surgeons' Museum. ^ 



inferior tibio-flbular liga 

 ment i 



Deep fibres of anterior inferior 

 tibio-flbular ligament 



^ of ex- 

 Anterior fasciculus I ternal 

 Posterior fasciculus > lateral ■, 

 Middle fasciculus | liga- (^ 

 ment 



Internal lateral ligament 



The anterior ligament (fig. 255) is a thin, membranous structure, which ex- 

 tends l)etween th(; lateral ligaments. It is attached above to the anterior border 

 of the internal malleolus, to a crest of bone just above the transverse groove at the 

 lower end of the tibia, to the anterior inferior tibio-fibular ligament, and to the 

 anterior border of the external malleolus. Below, it is attached to the rough upper 

 surface of the neck of the astragalus, in front of the fossa. Internally it is thicker, 

 and is fixed to the astragalus close to the facet for the inner malleolus, being 

 continuous with the internal lateral ligament, and passing forwards to blend 

 with the dorsal astragalo-sca])hoi(l ligament. Externally it is attached to the 

 astragalus, just l)elow and in front of the angle between the superior and lateral 

 facets, close to their edges, and joins the anterior fasciculus of the external lateral 

 ligament. It is in relation, in front with the tibialis anticus muscle, the anterior 



