120 ARTHROLOGY, OR ANATOMY OF ARTICULATIONS 



The capsular ligaments are thin and loose, strongest in front 

 arid externally; there is also a capsule for the anterior odonto- 

 atloid articulation. The sy no vial membranes are four in 

 number one for each capsular ligament, one for the anterior 

 articular surface of the odontoid, and one for its posterior 

 surface, a sort of bursa which may communicate with the 

 occipitoatloid joints. The atloaxoid joint possesses great 

 mobility, the greater part of the rotation of the head occurring 

 here, and none in the occipitoatloid joints. When the bones 

 are covered by articular cartilage, a sagittal section shows a 

 convexity upon a convexity. With the head equipoised and 

 eyes to the front, the muscles are at rest and ligaments tense. 

 When the head is rotated the point of the atlas sinks down 

 off the axis and a part projects; otherwise an already tense 

 ligament would become more tense in rotation did not the 

 points of attachment approach each other. 



The spinal column is connected to the cranium by ligaments 

 from the occiput to the atlas, from the occiput to the axis. 



The Articulations of the Atlas with the Occipital Bone 

 (Articuloatlantooccipitalis) 



There are anterior occipitoatlantal and posterior occipito- 

 atlantal, and two capsular ligaments. 



The anterior occipitoatlantal passes from the anterior 

 margin of the foramen magnum to the anterior arch of the 

 atlas; behind it are the odontoid ligaments. Laterally, it is 

 continuous with the capsular ligament. In the middle line 

 in front it is strengthened by a strong, narrow, rounded cord, 

 which is attached above to the basilar process of the occiput, 

 and below to the tubercle on the anterior arch of the atlas, 

 which is a continuation of the anterior common ligament. 



The posterior occipitoatlantal is membranous and blended 

 with the dura mater of the cord; it passes from the posterior 

 margin of the foramen magnum to the posterior arch of the 

 atlas. Laterally, it is pierced by the vertebral' artery and 

 suboccipital nerve. 



The capsular ligaments are loose, and enclose a synovial 

 membrane, which usually communicates with that between 

 the posterior surface of the odontoid and transverse ligament. 



