H)J 



THE SKELETON 



is n-ceiv(_'(l hv the jjosterior surface of the scaphoid. On the inner and lower part, 

 at the spot where the sustentaeular facet becomes confluent with that on the head, 

 thert" is a smaller facet separated by a ridge: this plays upon the calcaneo-scaphoid 

 or s])riiiLr li.Liaiiicnt. 



The OS trigonum. — (Occasionally the small jjortion of the astragalus posterior 

 \o tht' trochlear surface containing the groove Avhich lodges the flexor longus 



Fig. 168.— The Lkft Astragalus. (Plantar view.) 



GROOVE FOR THE FLEXOR LONGUS HALLUCIS 



FOR CALCANEUM 



FOR THE SUSTENTACULUM TAL! 



FOR THE CALCANEO-SCAPHOID (OR THE 

 SPRING) LIGAMENT 



liiilhiris tendon is separate from the rest of the astragalus, and is known as the os 

 trigonum, or secondary astragalus (fig. 169). 



Articulations. — The astragalus articulates with four bones, the tibia, fibula, 

 scaphoid, and calcaneum; and presents seven articular facets; and when the facet 

 for the sustentaculum tali is divided, as is so often the case, the articular surfaces 



Fig. 1G!).— Ax Astragalus with the Os Tkigoxum. 



cs trigonum 



are increased to eiglit. Sometiiiies it presents a facet on the outer margin of its 

 head f<»r tlie cuboid, thus increjusing tlie articular surfaces to nine. 

 Ligaments : — 



Internal lateral ligament (deltoid). 

 External lateral ligament. 

 Astragalo-.scaphoid. 



Calcanco-astragaloid (interosseous). 

 ICxternal calcaneo-astragaloid. 

 Posterior calcaneo-astragah )id. 



