ATLAS WITH OCCIPUT 183 



(2) THE LIGAMENTS AND JOINTS BETWEEN THE SKULL AND 

 SPINAL COLUMN, AND BET^^ EEN TLIE ATLAS AND AXIS 



(d) The Aeticulatiox of the Atlas avith the Occiput 

 Class. — Diarthrosis. Subdivision. — Doable Condi/larthrosis. 



This articulation consists of a pair of joints synnnetrically situated on either 

 side of the middle line. The parts entering into their formation are the cup-sliaped 

 superior articular processes of the atlas, and the condyles of the occipital bone. 

 They are united Ijy the folloAving ligaments: — 



1. Anterior occipito-atlantal. 3. Two capsular. 



2. Posterior occipito-atlantal. 4. Two anterior oblique. 



Tlie anterior occipito-atlantal ligament (fig. 194) is less than an inch (about 

 2 cm. ) wide, and is composed of densely woven filjres, most of which radiate 

 slightly outwards as they ascend from the front surface and upper margin of the 

 anterior arch of the atlas, to the anterior border of the foramen magnum; it is con- 

 tinuous laterally with the capsular ligaments, the fibres of which overlap its edges, 

 and take an opposite direction inwards and upwards. The central fibres ascend 

 vertically from the anterior tubercle of the atlas to the pharyngeal tubercle on the 

 occipital bone; they are thicker than the lateral fibres, and are continuous below 

 with the superficial part of the anterior atlanto-axoidean ligament, and through it 

 with the anterior common ligament of the vertel;)ral column. It is in relation, in 

 front, Avith the recti capitis antici minores ; and behind, Avith the central odontoid or 

 suspensory ligament. 



The posterior occipito-atlantal ligament (fig. 195) is broader, more mem- 

 branous, and not so strong as the anterior. It extends from the posterior surface 

 and upper border of the posterior arch of the atlas to the posterior margin of the 

 foramen magnum from condyle to condyle; being incomplete on either side for the 

 passage of the vertebral artery into, and suboccipital nerve out of, the canal. It is 

 somcAvhat thickened in the middle line by fibres, AA'hich pass from the posterior 

 tubercle of the atlas to the lower end of the occipital crest. It is not tightly 

 stretched betAveen the bones, nor does it limit their moA'ements; it corresponds with 

 the position of the ligamenta subflava, but has no elastic tissue in its composition. 

 It is in relation in front Avith the dura mater, Avhich is firmly attached to it; and 

 behind A\'ith the recti capitis pjostici minores^ and enters into the floor of the sub- 

 occipital triangle. 



The capsular ligaments (figs. 194 and 195) are very distinct and strongly 

 marked, except on the inner side, Avhere they are thin and formed only of short 

 membranous fibres. They are lax, and do not add much to the security of the joint. 

 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 l)ase of the 

 transverse process; these fibres take an oblique course upAvards and inwards, OA'er- 

 lapping the anterior occipito-atlantal. At the sides and behind, the capsule is 

 attached above to the margins of the occipital condyles; beloAv, it skirts the inner 

 edge of the foramen for the A^ertebral artery, and behind is attached to the promi- 

 nent tubercle OA^erhanging the groove for that A^essel ; these latter fibres are strength- 

 ened by a band running obliquely upAvards and iuAvards to the posterior margin of 

 the foramen magnum. 



The anterior oblique or lateral occipito-atlantal ligament (fig. 194) is an 

 accessory band Avliich strengthens tl)e capsule on the outer side. It is an oblique, 

 thick band of fil^res, sometimes cpiite separate and distinct from the rest, passing 

 upAvards and iuAvards from the upper surface of the transverse process bcA'ond the 

 costo-verteV)ral foramen to the jugular process of tlie occipital bone. 



The synovial membrane of these joints occasionally communicates Avith the 

 synovial sac between the odontoid process and the transverse ligament. 



