AKTICULATION OF SPINE WITH CKANIUM. 



311 



is arched in relation to the vertebral groove, and is therefore to some extent free, 

 in order to permit the passage of the posterior ramus of the first cervical nerve 

 and the vertebral artery. Not infrequently this arched border becomes ossified, 

 thus converting the groove on the bone into a foramen. 



A synovial stratum lines each of the articular capsules. 



There is no direct articulation between the epistropheus and the occipital bone, 

 but union between them is effected by means of the following accessory ligaments : 



The membrana tectoria (Fig. 296) is situated within the vertebral canal, and is 

 usually regarded as the upward continuation of the posterior longitudinal ligament 

 of the vertebral bodies. It extends from the posterior surface of the body of the 

 epistropheus to the basilar groove on the superior surface of the basilar part of the 

 occipital bone, spreading laterally on the circumference of the foramen magnum. 

 Some of its deepest fibres are attached to the atlas immediately above the atlanto- 

 epistropheal articulation. 



Subjacent to the membrana tectoria there is the ligamentum cruciatum atlantis 

 (Fig. 297), a structure which is very closely associated with the lig. transversum 

 atlantis. It consists of a cms transversum, formed by the superficial fibres of 

 the transverse ligament of the atlas ; a crus inferius, consisting of median longi- 

 tudinal fibres which are attached below to the posterior surface of the body of the 

 epistropheus, and above to the crus transversum ; and a crus superius, also median 

 and longitudinal, whose fibres extend from the crus transversum upwards to the 

 posterior surface of the basilar part of occipital bone, immediately subjacent to the 

 membrana tectoria. 



Ligamenta Alaria. The alar ligaments (O.T. check ligaments) (Fig. 29*7) are 

 two very powerful, short, and somewhat rounded bands. They are attached medially 

 to the sides of the summit of the dens, and laterally to the tubercle on the medial 

 aspect of the condylar portions of the occipital bone. 



Ligamentum Apicis Dentis. The ligament of the apex of the dens (O.T. 

 middle odontoid) (Fig. 297) consists of fibres running vertically upwards from the 

 apex of the dens to the median part of the anterior margin of the foramen magnum. 

 This ligament to some extent represents an intervertebral fibro-cartilage, in the 

 centre of which remains of the 

 notochord may be regarded as 

 present. 



Even in advanced life a 

 small lenticular mass of cartil- 

 age, completely surrounded by 

 bone, persists in the plane of 

 fusion between the dens and 

 the body of the epistropheus. 



Movements at these Joints. 



At the joints between occipital bone 

 and atlas the movements are very 

 simple, and consist essentially of 

 movements whereby the head is 

 elevated and depressed upon the 

 vertebral column (nodding move- 

 ments). In addition a certain 

 amount of oblique movement is 

 possible, during which great stabil- 

 ity is attained by resting the 

 anterior and posterior parts of 

 opposite condyles upon correspond- 

 ing parts of the atlas. 



The head and the atlas rotate 

 together upon the epistropheus, the 

 pivot of rotation being the dens, 

 and the amount of rotation is limited 

 by the ligamenta alaria. No rota- 

 tion can occur between the occiput 



and atlas, and stability between atlas and epistropheus is best attained after a slight amount 

 of rotation, similar to the oblique movement between occipital bone and atlas. 



Temporo-mandibular ligament 

 (anterior and posterior parts) 



Styloid process 



Stylo-mandibular ligament 



FIG. 298. MANDIBULAR JOINT. 



