VERTEBRAL COLUMN 07 



addition to the motions common to all vertebrae, namely, the dorso- 

 ventral and, to a less degree, the lateral, it rotates round the odontoid 

 process. 



Nomenclature of the Atlas. --The term atlas is used because this 

 vertebra supports the head, as Atlas was fabled to support the globe. 

 The word was introduced into anatomy by Vesalius (A.D. 1514-1564). 

 It had been known previously as the epistropheus (from Greek ry>/, 

 upon, and strepho, to turn), the vertebra, turning on the others; or as 

 protos spondylus, the first vertebra. The Germans call it, in addition 

 to der Atlas, der Truycr ; and the French la premiere vertebre servicale. 



KECAPITULATION OF CHARACTERS OF CERVICAL VERTEBRA. 



The body gradually increases in transverse width and reaches its 

 maximum in the seventh. The cephalo-caudal diameter is greatest in 

 the axis and decreases in the following order : the third, the fourth, 

 the fifth, the sixth, the seventh, the atlas. 



The neural arch is dorso-ventrally highest in the axis, and de- 

 creases in height as follows : atlas, seventh to third. It is transversely 

 widest in the atlas, and then decreases from the seventh to the axis. 

 The cephalo-caudal diameter is greatest in the axis, and decreases as 

 follows : the third, the atlas, the fourth, the fifth, the seventh, and the 

 sixth. 



The spinous process is longest in the seventh ; shorter in the axis 

 and from the sixth progressively to the third. Its cephalo-caudal 

 diameter is greatest in the axis. It is absent in the atlas and rudi- 

 mentary in the third. The spinous processes are directed toward the 

 skull. 



The transverse processes have the greatest cephalo-caudal diameter 

 in the atlas ; this diameter then decreases usually in the following 

 order : the sixth, the third, the fourth, the fifth, the axis, the seventh. 

 They are longest from root to tip in the atlas, and then decrease from 

 the fourth, the seventh, the third, to the axis. They are most complex 

 in the sixth and most simple in the axis. The transverse processes 

 arise from the body, and not dorsal ly from the pedicles. 



The arterial canal is found in all except the seventh. In the atlns 

 it does not traverse the entire cephalo-caudal width of the process. 



The cephalic articular processes spring from the pedicles, and the 

 caudal articular processes appear to be parts of the laminae. 



