

THE CERVICAL VERTEBRA 



99 



are joined, outside the foramen, by a bar of bone which exhibits a deep sulcus 

 on its upper surface for the passage of the corresponding spinal nerve. 1 



First Cervical Vertebra. The first cervical vertebra (Fig. 86) is named the 

 atlas because it supports the globe of the head. Its chief peculiarity is that it has 

 no body, and this is due to the fact that the body of the atlas has fused with that 

 of the next vertebra. Its other peculiarities are that it has no spinous process, 

 is ring-like, and consists of an anterior and a posterior arch and two lateral masses. 

 The anterior arch forms about one-fifth of the ring: its anterior surface is convex, 

 and presents at its center the anterior tubercle for the attachment of the Longus 

 colli muscles; posteriorly it is concave, and marked by a smooth, oval or circular 

 facet (fovea dentis), for articulation with the odontoid process (dens} of the axis. 

 The upper and lower borders respectively give attachment to the anterior atlanto- 

 occipital membrane and the anterior atlantoaxial ligament; the former connects 

 it with the occipital bone above, and the latter with the axis below. The posterior 

 arch forms about two-fifths of the circumference of the ring : it ends behind in the 

 posterior tubercle, which is the rudiment of a spinous process and gives origin to 

 the Recti capitis posteriores minores. The diminutive size of this process pre- 

 vents any interference with the movements between the atlas and the skull. 

 The posterior part of the arch presents above and behind a rounded edge for 



Anterior tubercle 



Outline of section of odontoid 

 process 



Outline cf section of trans- 

 verse atlantal ligament 



Foramen 

 transver- 

 sarium 



Groove for vertebral artery 

 and first cervical nerve 



Posterior tiibercle 



FIG. 86. First cervical vertebra, or atlas. 



the attachment of the posterior atlantooccipital membrane, while immediately 

 behind each superior articular process is a groove (sulcus arterioe vertcbralis) , 

 sometimes converted into a foramen by a delicate bony spiculum which arches 

 backward from the posterior end of the superior articular process. This groove 

 represents the superior vertebral notch, and serves for the transmission of the 

 vertebral artery, which, after ascending through the foramen in the transverse 

 process, winds around the lateral mass in a direction backward and medialward; it 

 also transmits the suboccipital (first spinal) nerve. On the under surface of the 

 posterior arch, behind the articular facets, are two shallow grooves, the inferior 

 vertebral notches. The lower border gives attachment to the posterior atlanto- 

 axial ligament, which connects it with the axis. The lateral masses are the most 

 bulky and solid parts of the atlas, in order to support the weight of the head. 

 Each carries two articular facets, a superior and an inferior. The superior facets 

 are of large size, oval, concave, and approach each other in front, but diverge 

 behind: they are directed upsvard, medialward, and a little backward, each forming 

 a cup for the corresponding condyle of the occipital bone, and are admirably 

 adapted to the nodding movements of the head. Not infrequently they are 



1 The costal element of a cervical vertebra not only includes the portion which springs from the side of tl)e body, but 

 the anterior and posterior tubercles and the bar of bone which connects them (Fig. 67). 



