OF THE TARSUS. 287 



V. Articulations of the Tarsus. 



1. ARTICULATIONS OF THE Os CALCIS AND ASTRAGALUS. 



The articulations between the os calcis and astragalus are two in number 

 anterior and posterior. They are arthrodial joints. The bones are connected 

 together by four ligaments : 



External Calcaneo-astragaloid. Posterior Calcaneo-astragaloid. 



Internal Calcaneo-astragaloid. Interosseous. 



The External Calcaneo-astragaloid Ligament (Fig. 190) is a short, strong, 

 fasciculus passing from the outer surface of the astragalus, immediately beneath 

 its external malleolar facet, to the outer surface of the os calcis. It is placed in 

 front of the middle fasciculus of the external lateral ligament of the ankle-joint, 

 with the fibres of which it is parallel. 



The Internal Calcaneo-astragaloid Ligament is a band of fibres connecting the 

 internal tubercle of the back of the astragalus with the back of the sustentaculum 

 tali. Its fibres blend with those of the inferior calcaneo-navicular ligament. 



The Posterior Calcaneo-astragaloid Ligament (Fig. 189) connects the external 

 tubercle of the astragalus with the upper and inner part of the os calcis ; it is a 

 short band, the fibres of which radiate from their narrow attachment to the 

 astragalus. 



The Interosseous Ligament forms the chief bond of union between the bones. 

 It consists of numerous vertical and oblique fibres attached by one extremity to the 

 groove between the articulating facets on the under surface of the astragalus ; by 

 the other to a corresponding depression on the upper surface of the os calcis. It 

 is very thick and strong, being at least an inch in breadth from side to side, and 

 serves to unite the os calcis and astragalus solidly together. 



The Synovial Membranes (Fig. 193) are two in number : one for the posterior 

 calcaneo-astragaloid articulation ; a second for the anterior calcaneo-astragaloid 

 joint. The latter synovial membrane is continued forward between the contiguous 

 surfaces of the astragalus and navicular bones. 



Actions. The movements permitted between the astragalus and os calcis are 

 limited to a gliding of the one bone on the other in a direction from before back- 

 ward, and from side to side. 



2. ARTICULATIONS OF THE Os CALCIS WITH THE CUBOID. 



The ligaments connecting the os calcis with the cuboid are four in number : 



-r^ , f Superior Calcaneo-cuboid. 



\ Internal Calcaneo-cuboid (Interosseous). 



TV, f Long Calcaneo-cuboid. 



-^Plantar. < , ' ^ , ,. , 



[ fehort Calcaneo-cuboid. 



The Superior Calcaneo-cuboid Ligament (Fig. 190) is a thin and narrow fasciculus 

 which passes between the contiguous surfaces of the os calcis and cuboid on the 

 dorsal surface of the joint. 



The Internal Calcaneo-cuboid (Interosseous) Ligament (Fig. 190) is a short 

 but thick and strong band of fibres arising from the os calcis, in the deep hollow 

 which intervenes between it and the astragalus, and closely blended, at its origin, 

 with the superior calcaneo-navicular ligament. It is inserted into the inner side of 

 the cuboid bone. This ligament forms one of the chief bonds of union between 

 the first and second rows of the tarsus. 



The Long Calcaneo-cuboid (Long Plantar) Ligament (Fig. 192), the more super- 

 ficial of the two plantar ligaments, is the longest of all the ligaments of the tarsus : 

 it is attached to the under surface of the os calcis, from near the tuberosities, as far 

 forward as the anterior tubercle ; its fibres pass forward to be attached to the 

 ridge on the under surface of the cuboid bone, the more superficial fibres being 



