ARTICULATIONS OF THE LOWER EXTREMITIES. 311 



This articulation is also strengthened by the insertion of the 

 lateral ligaments of the ankle joint into the os calcis. 



The Synovial Membrane forms a distinct cavity on the pos- 

 terior and larger articular face of the two bones, and is in con- 

 tact with the fatty matter in advance of the tendo-achillis. 



2. The Articulation of the Astragalus with the scaphoides is 

 formed by the convex head on the part of the former, and by 

 the concavity on the part of the latter. It is covered, above, by 

 a thin, broad ligament, with parallel and oblique fibres, which, 

 arising from the superior and internal face of the astragalus, are 

 implanted into the upper face of the scaphoides, some of its 

 fibres extending over to the cuneiform bones. It is covered, 

 above, by the tendons of the extensor muscles of the toes and 

 of the tibialis anticus. 



On the under surface of the foot, this articulation is support- 

 ed by two ligaments, called the Calcaneo Scaphoid, (Lig. Pla- 

 num,) from their origin and insertion. The interior one arises 

 from the internal margin of the lesser apophysis of the os cal- 

 cis, and, running obliquely forwards and inwards, is inserted 

 into the under and internal surface of the os scaphoides. It is 

 a very thick, flattened fasciculus, on the under surface of which 

 is formed the ligamentous trochleee, in which run the tendons 

 of the flexor pollicis and flexor longus digitorum, and which 

 surface is also in contact with the tendon of the tibialis posti- 

 cus. By subtending the head of the astragalus, it contributes 

 largely to the keeping of it in its place in the erect position. 

 The External Calcaneo Scaphoid Ligament, placed at the outer 

 margin of the last, arises from the under surface of the greater 

 apophysis of the os calcis, and running obliquely inwards arid 

 forwards, is implanted into the under external surface of the 

 scaphoides. It consists in two or more short, strong fasciculi. 



The Synovial Membrane of the articulation between the as- 

 tragalus and the scaphoides covers the articular faces of these 

 bones, and lines the ligaments above and below. A reflection 

 of it, also, lines the articulation between the os calcis and the 



