ARTICULATIONS OF THE ATLAS, AXIS, AND OCCIPITAL BONE. 155 



and round this centre a certain degree of rotation is permitted. In the lumbar region, the 

 centre of the circle in which the articular surfaces lie is placed behind, so that rotation is 

 prevented ; the articular processes, however, permit of lateral flexion, and by combination of 

 this with antero-posterior flexion, some decree of circumduction is produced. The articular 

 surfaces of the cervical vertebras, being- oblique and placed in nearly the same transverse plane, 

 allow neither pure rotation nor pure lateral flexion. They permit, besides forward and 

 backward motion, only one other, which is rotatory round a median axis, directed obliquely 

 from above and behind downwards and forwards the inferior articular process of one side 

 gliding 1 upwards and forwards on the opposing 1 surface, and that of the other side gliding 

 downwards and backwards, by which a combination of lateral flexion and rotation is 

 obtained. 



THE ABTICULATIONS OP THE ATLAS, AXIS, AND OCCIPITAL BONE. 



The atlas, axis, and occipital bone are connected by synovial articulations and 

 ligaments, without the presence of intervertebral discs. 



Two pairs of synovial articulations, surrounded by capsular ligaments, 

 connect the lateral masses of the atlas with the superior articular surfaces of the 



Fig. 179, CORONAL SECTION OP THE LOWER 



PART OF THE OCCIPITAL BONE, AND THE 

 FIRST TWO VERTEBRA, BEHIND THE 



ARTICULATIONS. (Allen Thomson, after 

 Arnold.) 



1, 1, posterior occipito-axial ligament 

 turned up in two layers ; 2, 2', vertical part, 

 and 3, 3, transverse or principal part of the 

 -cruciform ligament ; x , over the neck of 

 the odontoid process ; 4, 4, lateral odontoid 

 -or check ligaments ; 5, 5, accessory ligaments 

 .of the atlanto-axial capsules ; 6, 6, capsular 

 ligaments of the condylar articulations ; 

 7, 7, capsular ligaments of the atlanto-axial 

 .articulations. 



axis and with the condyles of the occipital bone. The atlanto-axial capsule is 

 strengthened at the inner and posterior part by an accessory ligament, directed 

 downwards and inwards to the body of the axis near the base of the odontoid 

 process. 



The transverse ligament of the atlas is a strong and thick band, which 

 extends across the ring of the atlas, and retains the odontoid process in its place. 



Fig. 180. HORIZONTAL SECTION THROUGH THE ODONTO- 

 ATLANTAL ARTICULATION. (Allen Thomson.) ^ 



1, cut surface of the odontoid process ; 2, cut surface of the 

 anterior arch of the atlas ; 3, transverse ligament ; between 1 

 And 2, the anterior synovial cavity, and between 1 and 3, the 

 posterior synovial cavity of the articulation ; 4, is placed on the 

 back part of the left superior articular process of the atlas ; 

 the anterior part has been partly removed by the section. For 

 the sake of distinctness, the synovial spaces are represented 

 wider than natural. 



It is attached on each side to the tubercle below the inner border of the superior 

 articular process. It is arched backwards behind the neck of the odontoid process, 

 and is broadened out in its central part. From the middle of its posterior surface 

 a short thin bundle of fibres passes down to be attached to the body of the axis, 

 while another passes up to the basilar process. These form, with the transverse 

 portion, the figure of a cross, and from this arrangement is derived the term 

 cruciform, which is sometimes applied to the transverse ligament and its appendages 

 together. 



