324 



THE ARTICULATIONS 



firmly attached on each side to a small tubercle on the inner surface of the lateral 

 mass of the atlas. As it crosses the odontoid process, a small fasciculus is derived 

 from its upper and lower borders ; the former passing upward, to be inserted into 

 the basilar process of the occipital bone ; the latter, downward, to be attached to 

 the posterior surface of the body of the axis ; hence, the whole ligament has 

 received the name of cruciform. The transverse ligament divides the ring of the 

 atlas into two unequal parts : of these, the posterior and larger serves for the 

 transmission of the cord and its membranes and the spinal accessory nerves ; 

 the anterior and smaller contains the odontoid process. Since the space between 

 the anterior arch of the atlas and the transverse ligament is smaller at the lower 



| CAPSULAR LIGA- 

 MENT and 

 synovial mem- 

 brane. 



APSULAR LIGAMENT 



and synovial 

 membrane. 



FIG. 228. Occipito-atloid and atlo-axoid ligaments. Front view. 



part than the upper (because the transverse ligament embraces firmly the narrow 

 neck of the odontoid process), this process is retained in firm connection with 

 the atlas after all the other ligaments have been divided. 



The Capsular Ligaments connect the articular processes of the atlas and axis, the 

 fibres being strongest on the posterior and internal part of the articulation, access- 

 ory ligaments ; these latter extend downward and inward to the body of the axis. 



There are four Synovial Membranes in this articulation : one lining the inner 

 surface of each of the capsular ligaments ; one between the anterior surface of the 

 odontoid process and the anterior arch of the atlas, the ado-odontoid joint; 

 and one between the posterior surface of the odontoid process and the transverse 

 ligament, the syndesmo-odontoid joint. The latter often communicates with 

 those between the condyles of the occipital bone and the articular surfaces of the 

 atlas. 



Actions. This joint allows the rotation of the atlas (and, with it, of the cra- 

 nium) upon the axis, the extent of rotation being limited by the odontoid liga- 

 ments. 



The principal muscles by which this action is produced are the Sterno-mastoid 

 and Complexus of one side, acting with the Rectus capitis anticus major, Splenius, 

 Trachelo-mastoid, Rectus capitis posticus major, and Inferior oblique of the other 

 side. 



