THE TARSAL JOINTS 



271 



The advantages of the obliquity and peculiar arrangement of the posterior 

 calcaneo-astragaloid articulation are seen in walking: (i) for the posterior facet of 

 the calcaneum receives the whole weight of the body when the heel is first placed 

 on the ground; (ii) by the upward pressure of this facet against the astragalus it 

 transfers the weight to the ball of the toes as the heel is raised, the hinder edge of 

 the sustentaculum tali and the anterior and outer part of the upper surface of 

 the calcaneum preventing the astragalus from being displaced too far forward 

 by the superincumbent weight; and (lii) the calcaneum serves to suspend the 

 astragalus when, with the heel raised by muscular action, the other foot is l:)eing 

 swung forwards. 



Tlie synovial membrane is the same as that of the astragalo-scaphoid joint. 

 The arteries and nerves are derived from the same sources as those of the medio- 

 tarsal joints. 



Fig. 255. — External View of ihk Ligamknisj ut ihl Jroox and Ankle. 



Anterb-iuferior tibio-flbular 

 ligament 



Postero-inferior tibio- 

 flbular ligament 



Fasciculus of posterior 

 ligament of ankle 



Externil cileaneo- 

 scaphoid lit;ameut 



Posterior fasciculus of 

 external lateral ligament 



Internal ealeaneo-cuboid 



Dorsal External Middle fasciculus of external lateral 

 calcaneo- calcaneo- ligament of the ankle 



cuboid astragaloid 

 ligament 



(h) The Articul.a.tions of the Anterior Part of the Tarsus 



These include (i) the cubo-scaphoid; (ii) scapho-cuneiform; (iii) intercunei- 

 form; and (iv) cubo-cuneiform joints. 



(i) The Cubo-scaphoid Union 



Class. — Diarthrosis. Subdivision. — A rthrodia. 



The ligaments which unite the cuboid and scaphoid are: 



Dorsal. Plantar. Interosseous. 



The dorsal cubo-scaphoid ligament (fig. 256) runs forwards and outwards from 

 the outer end of the dorsal surface of the scaphoid to the middle third of the inner 



