136 TARSAL ARTICULATION. 



fibres attached superiorly by its apex to the internal malleolus, and 

 inferiorly by an expanded base to the astragalus, os calcis, and sca- 

 phoid bone. Beneath the superficial layer of this ligament is a much 

 stronger and thicker fasciculus of fibres, which connects the apex of 

 the internal malleolus with the side of the astragalus. 



This internal lateral ligament is covered in and partly concealed 

 by the tendon of the tibialis posticus, and at its posterior part is in 

 relation with the tendon of the flexor longus digitorum, and of the 

 flexor longus pollicis. 



The external lateral ligament consists of tb~ee strong fasciculi, 

 which proceed from the inner side of the external malleolus, and 

 diverge in three different directions. The anterior fasciculus passes 

 forwards, and is attached to the .astragalus ; the posterior, back- 

 wards, and is connected with the astragalus posteriorly; and the 

 middle, longer than the other two, descends to be inserted into the 

 outer side of the os calcis. 



" It is the strong union of this bone," says Sir Astley Cooper, with 

 the tarsal bones by means of the external lateral ligaments, " which 

 leads to its being more frequently fractured than dislocated." 



The transverse ligament of the tibia and fibula occupies the place 

 of a posterior ligament. It is in relation, behind, with the posterior 

 tibial vessels and nerve, and with the tendon of the tibialis posticus 

 muscle ; and in front, with the extra-synovial adipose tissue, and 

 synovial membrane. 



The Synovial membrane invests the cartilaginous surfaces of the 

 tibia and fibula, sending a duplicature upwards between their lower 

 ends ; and the upper surface and two sides of the astragalus. It is 

 then reflected upon the anterior and lateral ligaments, and upon the 

 transverse ligament posteriorly. 



Actions. The movements of the ankle joint are Jlexion and ex- 

 tension only, without lateral motion. 



5. Articulation of the Tarsal Bones. The ligaments which con- 

 nect the seven bones of the tarsus to each other are of three kinds, 



Dorsal, 



Plantar, 



Interosseous. 



The dorsal ligaments are small fasciculi of parallel fibres, which 

 pass from each bone to all the neighbouring bones with which it 

 articulates. The only dorsal ligaments deserving of particular 

 mention are, the external and posterior calcaneo-astragaloid, 

 which, with the interosseous ligament, complete the articulations 

 of the astragalus with the os calcis; the superior and internal 

 calcaneo-cuboid ligaments ; and the superior astragalo-scaphoid 

 ligament. The internal calcaneo-cuboid and the superior calcaneo- 

 scaphoid ligament, which are closely united posteriorly in the deep 

 groove which intervenes between the astragalus and os calcis, 

 separate anteriorly to reach their respective bones, and form the 

 principal bond of connexion between the first and second range of 



