i8 



Anatomy of Skeleton 



process, thus holding the process up against the front arch of the Atlas, and completing 

 a collar round the process that grasps it tightly, with intervening bursse : evidently 

 with such a band, the Atlas cannot move away from the odontoid, but can rotate 

 round it as a centre. This transverse ligament is connected by upper and lower crura 

 of vertical fibres with the occiput and back of the body of the Axis respectively, but 

 these bands are comparatively weak and do not seem to be of much importance in 

 limiting movement : the whole structure is sometimes referred to as the cruciform 

 ligament (Fig. 13). 



The second system consists of strong and thick bands connecting the upper end 

 of the odontoid process with the margin of the foramen magnum in the occipital bone : 

 there is one of these on each side, lateral occipito-odontoid or check ligaments, and a 

 feeble median one, between the process and the front margin of the foramen, termed 



Occipital. 



FIG. 13. The ligaments of the occipito-atlo-axoid articulation exposed by 

 removal of the neural arches and contents of the canal. The posterior 

 common lig. is continuous with the membrana tectoria, which has 

 been divided and turned back at C.C. to expose the cruciform lig. A. 

 This covers the back of the odontoid, but the check ligaments B. can 

 be seen passing to the upper end of the process from the margin of the 

 foramen magnum. Access, is the accessory atlo-axoid lig. The 

 median " suspensory " lig. is hidden by the upper crus of the cruciform 

 Ug. 



the middle odontoid or suspensory ligament. The middle band has no mechanical 

 value, being only the continuation into the skull of the perinotochordal tissues, but 

 the lateral bands are of prime importance. Flexion and extension between the Atlas 

 and Axis is effectively prevented by the close grip obtained by the anterior arch and 

 transverse ligament on the odontoid process. On the other hand, rotation between 

 the skull and the Atlas is checked as a result of the deep concavity of the upper articular 

 surfaces of the Atlas : any attempt at rotation of the Occipital tends at once to lift 

 the bone up on to the raised front and back margins of these surfaces and thus imme- 

 iiately tightens the check ligaments and anterior occipito-atloid, and is moreover 

 resisted by all the short muscles passing to the neighbouring skull base from the 

 column. 



Thus, for practical purposes, we may look on the skull and Atlas as one mass 

 rotating on the Axis, and on the Atlas and Axis as one mass on which the skull can 



