ARTICULATION OF ATLAS WITH OCCIPUT 



219 



In front, the capsule descends upon the atlas, to be attached, some distance below the 

 articular margin, to the front surface of the lateral mass and to the base of the transverse proc- 

 ess; these fibres take an oblique com-se upward and medialward, overlapping the anterior atlanto- 

 occipital. At the sides and behind, the capsule is attached above to the margins of the occipital 

 condyles; below, it skirts the medial edge of the foramen for the vertebral artery, and behind 

 is attached to the prominent tubercle overhanging the groove for that vessel; these latter fibres 

 are strengthened by a band running obliquely upward and medialward to the posterior margin 

 of the foramen magnum. 



The anterior oblique or lateral occipito-atlantal ligament is an accessory 

 band Avhich strengthens the capsule laterally (fig. 259). It is an oblique, thick 

 band of fibres, sometimes quite separate and distinct from the rest, passing 

 upward and medialward from the upper surface of the transverse process beyond 

 the costo-transverse foramen to the jugular process of the occipital bone. 



The synovial membrane of these joints occasionally communicates with the 

 synovial sac between the dens (odontoid process) and the transverse ligament. 



The arterial supply is derived from twigs of the vertebral, and occasionally from twigs 

 from the meningeal branches of the ascending pharyngeal. 



Fig. 259. — Anterior View" of the Upper End of the Vertebral Column. 



Continuation of 

 the anterior 

 longitudinal 

 ligament of 

 the vertebral 

 column 



Anterior atlanto 

 occipital liga- 

 ment 



i 



The anterior oblique or 

 lateral occipitoatlantal 

 ligament 



Atlanto-epistrophic 

 articular capsule 



Articular capsules of arti- 

 cular processes between 

 axis and the third, the 

 third and fourth, and 

 the fourth and fifth cer- 

 vical vertebrae 



Anterior atlanto- 

 epistrophic ligament 



Body of axis 



Short vertebral 

 ligament 



Anterior longitudinal 

 ligament 



'"'^n- 



The nerve-supply comes from the anterior division of the suboccipital nerve. 



Movements. — By the symmetrical and bilateral arrangement of these joints, security and 

 strength are gained at the expense of a very small amount of actual articular surface; the basis 

 of support and the area of action being equal to the width between the most distant borders 

 of the joint. 



The principal movement permitted at these joints is of a jginglymoid character, producing 

 flexion and extension upon a transverse axis drawn across the condyles at theii* slightly con- 

 stricted parts. 



In flexion, the forehead and chin drop, and what is called the nodding movement is made; 

 in extension, the chin is elevated and the forehead recedes. 



There is also a slight amount of gliding movement, either directly lateral, the lateral edge 

 of one condyle sinking a little within the lateral edge of the socket of the atlas, and that of the 

 opposite condyle projecting to a corresponding degree. The head is thus tilted to one side, and 

 it is even possible that the weight of the skull may be borne almost entirely on one joint, the 

 articular surfaces of the other being thrown out of contact. 



Or the movement may be obliquely lateral, when the lower side of the head wiU be a trifle 



