58o A MANUAL OF ANATOMY 



The synovial membrane, though distinct from that of the posterior 

 astragalo-calcaneal joint, is continuous in front with that of the 

 astragalo-navicular articulation. 



The arterial supply and nerve-supply are the same as for the 

 astragalo-navicular articulation. 



Movements between the Astragalus and Os Calcis. — The movements at the 

 astragalo-calcaneal joints are abduction, adduction, and rotation. In 

 abduction the foot and toes are turned outwards, and in adduction they are 

 turned inwards, these movements being associated with a certain amount of 

 rotation round an axis passing from the inner side of the neck of the astra- 

 galus downwards, backwards, and outwards to the lower and outer part of 

 the tuber calcis. In adduction or inversion the posterior facet of the os 

 calcis moves forwards and downwards upon the astragalus, and the front 

 part of the os calcis is carried slightly inwards. During the movements 

 the navicular bone rotates on the head of the astragalus, and the cuboid 

 bone moves along with the os calcis. 



II. Astragalo-navicular Joint. — This belongs to the class 

 diarthrosis, and to the subdivision enarthrosis. It is in direct 

 continuity behind with the anterior astragalo-calcaneal joint, with 

 which it shares its synovial membrane, and the two articulations 

 are sometimes described as one composite joint under the naiAe of 

 the astragalo-calcaneo-navicular joint. The ligaments are astragalo- 

 navicular, external or superior calcaneo-navicular, and internal or 

 inferior calcaneo-navicular, or spring, ligament. 



The astragalo-navicular ligament is a thin membrane which 

 covers the joint on its dorsal aspect. It is attached posteriorly 

 to the upper margin of the head of the astragalus close behind the 

 cartilage, and also to its outer and inner surfaces. Anteriorly it 

 is attached to the dorsal surface of the navicular bone. Its fibres are 

 arranged in a radiating manner, and converge towards the navicular 

 bone. At the attachment to the astragalus they frequently form 

 three bands, outer, dorsal, and inner, which, however, are continuous 

 with one another. 



The external or superior calcaneo-navicular ligament has been 

 described in connection with the anterior astragalo-calcaneal joint, 

 of which it ranks as the external ligament. 



The internal or inferior calcaneo-navicular ligament is one 

 of the most important ligaments of the foot, and is known as 

 the spring ligament. It is a broad, thick, strong band of the 

 consistence of fibro-cartilage, and is composed of fibrous and elastic 

 tissues. Posteriorly it is attached to the front of the sustentaculum 

 tali and the adjacent portion of the plantar surface of the os calcis. 

 Anteriorly it is attached to (i) the plantar surface of the navicular 

 bone, (2) the back of its tuberosity, and (3) the inner part of its 

 dorsal surface. It is directed forwards and inwards, and covers 

 the joint on its inner and lower aspects. Internally it blends 

 with the anterior part of the internal lateral ligament of the 

 ankle-joint and the astragalo-navicular ligament, and externally 

 it blends with the external calcaneo-navicular ligament. The 

 superior or deep surface of the ligament is in contact with a special 



