OF THE ATLAS WITH THE OCCIPITAL BONE. 271 



small fasciculus is derived from its upper and lower borders; the former passing 

 upwards, to be inserted into the basilar process of the occipital bone ; the latter, 

 downwards, to be attached to the root of the odontoid process; hence, the whole 

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



Fig. 186. Articulation between Odontoid Process and Atlas. 



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 ; the anterior and 

 smaller contains the odontoid process. Since the lower border of the space 

 between the anterior arch of the atlas and the transverse ligament is smaller 

 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, when all the other ligaments have been divided. 



The Capsular Ligaments are two thin and loose capsules, connecting the 

 articular surfaces of the atlas and axis, the fibres being strongest on the an- 

 terior and external part of the articulation. 



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 ; and one between the 

 posterior surface of the odontoid process and the transverse ligament. The 

 latter often communicates with those between the condyles of the occipital 

 bone and the articular surfaces of the atlas. 



Actions. This joint is capable of great mobility, and allows the rotation of 

 the atlas, and, with it, of the cranium upon the axis, the extent of rotation 

 being limited by the odontoid ligaments. 



The ligaments connecting the spine with the cranium may be divided into 

 two sets, those connecting the occipital bone with the atlas, and those connect- 

 ing the occipital bone with the axis. 



III. ARTICULATION OF THE ATLAS WITH THE OCCIPITAL BONE. 



This articulation is a double arthrodia. Its ligaments are the 



Two Anterior Occipito-atloid. 

 Posterior Occipito-atloid. 

 Two Lateral Occipito-atloid. 

 Two Capsular. 



Of the two Anterior Occipito-atloid Ligaments (Fig. 184), the superficial is a 

 strong, narrow, rounded cord, attached, above, to the basilar process of the 

 occiput ; below, to the tubercle on the anterior arch of the atlas ; the deeper 

 ligament is a broad and thin membranous layer, which passes between the 

 anterior margin of the foramen magnum above, and the whole length of the 

 upper border of the anterior arch of the atlas below. This ligament is in rela- 

 tion, in front, with the Eecti Antici Minores; behind, with the odontoid ligaments. 



