TARSAL ARTICULATIONS. 165 



The internal lateral or deltoid ligament is a triangular layer of fibres, 

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

 an expanded base to the astragalus, os calcis, and scaphoid bone. Be- 

 neath the superficial layer of this ligament is a much stronger and thicker 

 fasciculus, which connects the apex of the internal malleolus with the side 

 of the astragalus. v 



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 with that of the flexor 

 longus pollicis. 



The external lateral ligament consists of three 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, backwards, 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 ves- 

 sels 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 duplicate upw r ards 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 flexion and extension 

 only, without lateral motion. 



5. Articulations of the Tarsal Bones. The ligaments which connect 

 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-aslragaloid, which, with the interosseous ligament, 

 complete the articulation of the astragalus with the os calcis ; the superior 

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

 the superior calcaneo-scaphoid ligament, which are closely united pos- 

 teriorly in the deep groove which intervenes between the astragalus and 

 os calcis, separate anteriorly to reach their respective bones ; they form 

 the principal bond of connexion between the first and second range of 

 the bones of the foot. It is the division of this portion of these ligaments 

 that demands the especial attention of the surgeon in performing Chopart's 

 operation. 



The plantar ligaments have the same disposition on the plantar surface 

 of the foot; three of them, however, are of a large size, and have especial 

 names, viz. the 



Calcaneo-scaphoid Long calcaneo-cuboid, Short calcaneo-cuboid. 



