22 OSTEOLOGY, OR ANATOMY OF OSSEOUS SYSTEM 



margin of each is a tubercle for the transverse ligament. The 

 inferior articular surfaces are slightly convex, nearly circular, and 

 do not wholly cover or fit the superior processes of the axis. The 

 posterior arch presents in the median line either a ridge, hollow, 

 or small tubercle. If a spinous process were well developed 

 here, nodding of the head would be prevented. Just behind 

 the lateral mass is a smooth sinus, the vertebral notch. The 

 transverse processes are not bifid are large and strong for 

 attachment of rotatory muscles. 



Varieties. The posterior or anterior bony arch may be 

 incomplete; the anterior root of the transverse process may 

 be ligamentous. A spicule of bone may bridge over the superior 

 vertebral notch, and the canal formed be subdivided by other 

 spicules. The artery and vein go through the upper subdivision, 

 the suboccipital nerve through the lower. 



THE Axis (EPISTROPHEUS) 



The second vertebra forms an axis upon which the atlas 

 carrying the head rotates. The body of the atlas is joined 

 upon that of the axis in the form of a tooth-like process, the 

 odontoid. Its apex is pointed, and just below is an enlarge- 

 ment or head, both giving attachment to bands of the check 

 ligament. 



The process has in front a smooth articular surface for the 

 arch of the atlas, and behind a smooth groove for the transverse 

 ligament. This makes a slight constriction, but hardly a 

 neck. 



The anterior surface of the body presents a slight ridge 

 separating two depressions. The superior articular surface 

 lies close to the odontoid process, upon the body in part and 

 upon the pedicles; they look up and out. The inferior articular 

 surfaces are behind the upper, and resemble corresponding 

 ones in the cervical region. The spinous process is grooved 

 inferiorly is very large and bifid, in contradistinction to that 

 of the atlas. The transverse processes are short, with the 

 anterior tubercle nearly suppressed. The inferior vertebral 

 notch is in front of the articular surface, which is the rule 

 for both notches below this in the column. 



