426 THE ANATOMY OF THE HOESE 



the tibia ; tliey take a course backwards and downwards, and terminate, 

 one on the astragalus, the other upon the lower and inner surface of the 

 OS calcis. The internal deep ligament is an extremely thin band ; it is 

 attached above to the tibia, just below the attachment of the middle liga- 

 ment, and below to the astragalus, nearly at the same point as the superior 

 insertion of the middle ligament. 



The anterioi' ligament is a thin layer, formed of decussating fibres, 

 stronger without than within, attached by its superior edge to the tibia, and 

 by its inferior edges to the astragalus and to the os cuneiforme parvum. 



The 2}osterior ligament, similar in structure to the anterior, is attached to 

 the same bones, behind their articular surfaces. 



The synovial membrane is developed on the internal surface of the two 

 capsular ligaments, covered also by the three internal and the external deep 

 ligaments. 



Movements. — This joint allows only of flexion and extension ; but to 

 avoid contact between the foot and the tibia in the act of flexion, the tibio- 

 astragalan articulation causes the bones below to deviate outwards, owing 

 to the obliquity of the articular surfaces. 



ARTICULATIONS BETWEEN THE BONES 

 OF THE TARSUS 



The calcaneo-astragalan articulation between the bones of the first 

 row is a compound arthrodia, resulting from the coaptation of three or four 

 articular surfaces on the posterior face of the astragalus to corresponding 

 facettes on the antero-inferior part of the os calcis. The lateral ligaments 

 of the tibio-tarsal articulation are common to this joint ; and we also have 

 four ligaments proper to it, a superior, external, internal, and an interosseous 

 ligament. 



The superior astragalo-calcanean ligament, formed of very short and 

 parallel fibres thrown from one bone to the other, is situated near the 

 superior extremity of the trochlear astragalan surface, and lined by the 

 synovial membrane of the tibio-tarsal articulation. 



The lateral ligaments are two very thin bundles, which unite the os calcis 

 to the astragalus laterally, hidden under the ligaments which bind the tibia 

 to the tarsus. 



The interosseous ligament is very strong, and occupies a great part of 

 the roughened excavations which separate the arthrodial surfaces of the 

 OS calcis and astragalus. These do not possess proper synovial membranes, 

 that is, membranes proper to each, with the exception of one, formed on 

 the upper and outer part of this articulation, where a distinct synovial 

 membrane exists. The superior arthrodial surface is, however, sometimes 

 supplied with synovial membrane, by a prolongation from the tibio-tarsal 

 capsule. Two prolongations ascend from the capsule of this articulation 

 below the inferior arthrodial surfaces of the os calcis and astragiilus, and 

 thus facilitate a gliding motion, which is very limited. 



The movements are so limited as to be almost null. 



In the articulations of the bones of the second row among them- 

 selves, the cuboid bone joins with the os scaphuides by two arthrodial sur- 



