232 



ARTICULATIONS. 



3. The articulation between the astragalus and scaphoid is an enarthrodial 

 joint ; the rounded head of the astragalus being received into the concavity formed 

 by the posterior surface of the scaphoid, the anterior articulating surface of the 

 calcaneum, and the upper surface of the calcaneo-scaphoid ligament, which fills up 

 the triangular interval between these bones. The only 'ligament of this joint is 

 the superior astragalo-scaphoid, a broad band of ligamentous fibres, which passes 

 obliquely forwards from the neck of the astragalus, to the superior surface of the 

 scaphoid bone. It is thin and weak in texture, and covered by the Extensor 

 tendons. The inferior calcaneo-scaphoid supplies the place of an inferior liga- 

 ment. 



The Synovial Membrane which lines the joint is continued forwards from the 

 anterior calcaneo-astragaloid articulation. This articulation permits of consider- 

 able mobility ; but its feebleness is such as to occasionally allow of dislocation 

 of the astragalus. 



The Synovial Membranes (fig. 146) found in the articulations of the tarsus are 

 four in number : one for the posterior calcaneo-astragaloid articulation ; a second 

 for the anterior calcaneo-astragaloid and astragalo-scaphoid articulations ; a third 



Fig. 146. Oblique Section of the Articulations of the Tarsus and Metatarsus. 

 Showing the Six Synovial Membranes. 



for the calcaneo-cuboid articulation; and a fourth for the articulations between 

 the scaphoid and the three cuneiform, the three cuneiform with each other, the 

 external cuneiform with the cuboid, and the middle and external cuneiform with 

 the bases of the second and third metatarsal bones. The prolongation which lines 

 the metatarsal bones passes forwards between the external and middle cuneiform 

 bones. A small synovial membrane is sometimes found between the contiguous 

 surfaces of the scaphoid and cuboid bones. 



Actions. The movements permitted between the bones of the first row, the 

 astragalus and os calcis, are limited to a gliding upon each other from before 

 backwards, and from side to side. The gliding movement which takes place 

 between the bones of the second row is very slight, the articulation between the 

 scaphoid and cuneiform bones being more movable than those of the cuneiform 

 with each other and with the cuboid. The movement which takes place between 

 the two rows is more extensive, and consists in a sort of rotation, by means of 

 which the sole of the foot may be slightly flexed, and extended, or carried inwards 

 and outwards. 



