ATLANTO-EPISTROPHIC JOINTS 



221 



The ligaments which unite tlie epistropheus and atlas are : — 



1. The anterior atlanto-epistrophic. 3. Two articular capsules (for lateral 



joints). 



2. The posterior atlanto-epistrophic. 4. The transverse ligament. 



5. The atlanto-dental articular capsule. 



The anterior atlanto-epistrophic ligament (figs. 259 and 260) is a narrow but 

 strong membrane filling up the interval between the lateral joints. It is attached 

 above to the front surface and lower border of the anterior arch of the atlas, and 

 below to the transverse ridge on the front of the body of the epistropheus. Its 

 fibres are vertical, and are thickened in the median line by a dense band which is 

 a continuation upward of the anterior longitudinal ligament of the vertebral 

 column. 



This band is fixed above to the anterior tubercle of the atlas, where it becomes continuous 

 with the central part of the anterior atlanto-occipital ligament (fig. 259) ; it is sometimes sepa- 

 rated by an interval from the deeper ligament, and is often described as the superficial atlanto- 

 epistrophic ligament. It is in relation with the longus colli muscle. 



The posterior atlanto-epistrophic ligament (fig. 260) is a deeper, but thinner 

 and looser membrane than the anterior. It extends from the posterior root of the 

 transverse process of one side to that of the other, projecting laterally beyond 

 the posterior part of the capsules which are connected with it. It is attached 

 above to the posterior surface and lower edge of the posterior arch of the atlas, 

 and below to the superior edge of the laminae of the epistropheus on their dorsal 

 aspect. 



It is denser and stronger in the median line, and has a layer of elastic tissue on its anterior 

 surface like the ligamenta flava, to which it corresponds in position. It is connected in front 

 with the dura mater; behind, it is in relation with the inferior oblique muscles, and is perforated 

 at each side by the second cervical nerve. 



1. The Lateral Atlanto-epistrophic Joints are provided with short, 

 ligamentous fibres, forming articular capsules (fig. 259), which completely sur- 

 round the lateral articular facets. Lateral to the canal they are attached some 

 little distance from the articular margins, extending along the roots of the 



{ 



Pig. 261. 



-Horizontal Section through the Lateral Masses of the Atlas and the 

 Top of the Dens (Odontoid Process). 



Atlanto-dental 

 synovial sac 



Transverse dental 

 synoviaJ sac 



Atlanto-dental 

 articular capsule 

 Transverse 



ligament 

 Posterior longitud- 

 inal ligament and 

 tectorial membrane 



Dura mater 



transverse processes of the epistropheus nearly to the tips, but between the roots 

 they skirt the medial edge of the costo-transverse foramina. They are strength- 

 ened in front and behind by the atlanto-epistrophic ligaments. 



^Medially each capsule is thinner, and attached close to the articular margins, being strength- 

 ened behind by a strong band of slightly oblique fibres passing upward along the lateral edge of 

 the tectorial membraneirom the body of the epistropheus to the lateral mass of the atlas behind 

 the transverse ligament| some of these fibres pass on, thickening and blending with the atlanto- 

 occipital capsule, to be inserted into the margin of the foramen magnum. This band is some- 

 times called the accessory band (fig. 263). 



There is a synovial membrane for each joint. 



2. The Central Atlanto-epistrophic Joint, although usually described as 

 one, is composed of two articulations, which are quite separate from one another: 



<Ji 'i^y\^ ^n 



1^ 



