230 



THE ARTICULATIONS. 



inward, attached above to the jugular process of the occipital bone ; below, to the 

 base of the transverse process of the atlas. 



The Capsular Ligaments surround the condyles of the occipital bone, and con- 

 nect them with the articular processes of the atlas ; they consist of thin and loose 

 capsules, which enclose the synovial membrane of the articulation. 



Synovial Membranes. There are two synovial membranes in this articulation, 

 one lining the inner surface of each of the capsular ligaments. These occasionally 

 communicate with that between the posterior surface of the odontoid process and 

 the transverse ligament. 



Actions. The movements permitted in this joint are flexion and extension, 

 which give rise to the ordinary forward and backward nodding of the head, besides 



FIG. 155. Articulation between odontoid process and atlas. 



slight lateral motion to one or the other side. When either of these actions is 

 carried beyond a slight extent, the whole of the cervical portion of the spine assists 

 in its production. Flexion is mainly produced by the action of the Rectus capitis 

 anticus major et minor and the Sterno-mastoid muscles ; extension by the Rectus 

 capitis posticus major et minor, the Superior oblique, the Complexus, Splenius, 

 and upper fibres of the Trapezius. The Recti laterales are concerned in the lat- 

 eral movement, assisted by the Trapezius, Splenius, Complexus, and the Sterno- 

 mastoid of the same side, all acting together. According to Cruveilhier, there is a 

 slight motion of rotation in this joint. 



IV. Articulation of the Axis with the Occipital Bone. 



Occipito-axial. 



Three Odontoid. 



To expose these ligaments the spinal canal should be laid open by removing 

 the posterior arch of the atlas, the laminae and spinal process of the axis, and the 

 portion of the occipital bone behind the foramen magnum, as seen in Fig. 156. 



The Occipito-axial Ligament (apparatus ligamentosus colli) is situated within 

 the spinal canal. It is a broad, strong band, which covers the odontoid process 

 and its ligaments, and appears to be a prolongation upward of the posterior common 

 ligament of the spine. It is attached, below, to the posterior surface of the body 

 of the axis, and, becoming expanded as it ascends, is inserted into the basilar 

 groove of the occipital bone, in front of the foramen magnum, Avhere it becomes 

 blended with the dura mater of the skull. 



Relations. By its anterior surface with the transverse ligament ; by its posterior 

 surface with the dura mater. 



The Odontoid or Check Ligaments (alar ligaments) are strong, rounded, fibrous 

 cords, which arise one on either side of the upper part of the odontoid process, and, 

 passing obliquely upward and outward, are inserted into the rough depressions on 

 the inner side of the condyles of the occipital bone. In the triangular interval left 

 between these ligaments another strong fibrous cord (lig amentum suspensorium, or 



