LIGAMENTS OF OCCIPUT AND EPISTROPHEUS 



223 



(c) The Ligaments uniting the Occiput and Epistropheus 



The following ligaments unite bones not in contact, and are to be seen from 

 the interior of the canal after removing the posterior arches of the epistropheus 

 and atlas and posterior ring of the foramen magnum : — 



1. The tectorial membrane. 



2. The crucial ligament. 



3. Two alar (or check) ligaments. 



4. The apical dental ligament. 



The tectorial membrane (occipito-cervical ligament) (figs. 261, 262, and 263) 

 consists of a ver}^ strong band of fibres, connected below to the upper part of 

 the body of the third vertebra and lower part of the body of the epistropheus 

 as far as the root of the dens. It is narrow below, but widens out as it ascends, 

 to be fastened to the basilar groove of the occiput. Laterally, it is connected 

 with the accessory fibres of the atlanto-epistrophic capsule. It is really only 

 the upward prolongation of the deep stratum of the posterior longitudinal 

 ligament, the superficial fibres of which run on to the occipital bone without 

 touching the epistropheus, thus giving rise to two strata. It is in relation in 

 front with the crucial ligament. 



Fig. 262. — The Superficial Layer of the Posterior Longitudinal Vertebral Liga- 

 ment HAS been Removed to show its Deep or Short Fibres. These Deep Fibres 

 form the Tectorial Membrane. Viewed from behind. 



Membrana tectoria, i. e., 

 the deep stratum of the 

 posterior longitudinal 



vertebral ligament 



Transverse process of atlas 



Atlemto-epistrophic ar- 

 ticular capsule 



The crucial ligament has been already described (see p. 222). 



The alar (or check) ligaments (figs. 260 and 263) are two strong rounded 

 cords, which extend from the sides of the apex of the dens, transversely lateral- 

 ward to the medial edge of the anterior portion of the occipital condyles. 



They are to be seen immediately above the upper border of the transverse ligament, which 

 they cross qbhquely owing to its forward curve at its attachments to the atlas. Some of their 

 fibres occasionally run across the middle line from one alar ligament to the other. At the dens 

 they are connected with the atlanto-dental capsule, and at the condyles they strengthen the 

 atlanto-occipital articular capsule. 



The apical dental or suspensory ligament (figs. 260 and 263) consists of a 

 slender band of fibres ascending from the sumhiit of the dens to the lower surface 

 of the occipital bone, close to the foramen magnum. It is best seen from the 

 front, after removing the anterior atlanto-occipital ligament, or from behind by 

 drawing aside the crucial ligament. 



