THE SPINAL COLUMN AND BACK. 151 



in the 2nd sacral in the 5th month or later ; in the 3rd they 

 may not appear. In the 4th and 5th sacral and 1st coccygeal 

 vertebrae only vestiges of the neural arches are formed. These 

 vertebrae retain the early foetal type shown in figure 119 B. 

 In the remaining coccygeal vertebrae only the centres for the 

 bodies appear. The centres for ossification of the bodies of the 

 vertebrae appear first in the mid dorsal region (6th dorsal). From 

 that point they spread forwards and backwards, the centres for 

 the odontoid process appearing at the 4th month and that for 

 the 5th sacral at the 5th month, while the last coccygeal does 

 not appear until about the 20th or 25th year (Fig. 120 A). 



The Atlas and Axis. — The atlas represents the completed 

 bow of the 1st cervical vertebra. The body of the vertebra 

 fuses with the body of the 2nd, and forms the odontoid process. 

 A remnant of the disc between the 1st and 2nd vertebrae can 



{'•h—basi-sph. 



term, of notoch. 

 -basi-occio. 

 -susp. fig. 

 .1st hypoeh. bow (atlas) 



- 1st centrum 



-2nd hypoeh. bow. 



-2nd centrum 



s.i 3rd bow and 

 {centrum 



^notochord 



Flo. 121.— A diagrammatic section of the Foetal Axis, Atlas, and Basi-occipital. 



sometimes be seen when the odontoid is split open. The sus- 

 pensory ligament is the representative of the disc between the 

 last occipital segment and the 1st cervical (Fig. 121). 



Occipito-atlanto-axial Articulations. — In the intervertebral 

 discs of the cervical region there is at each side, between the 

 lateral lips of the vertebral bodies, a small articular cavity (Fig. 

 122). It is situated between the parts of the body formed from 

 the neural arches and in front of (ventral to) the issuing spinal 

 nerves. Between the axis and atlas this articulation is greatly 

 enlarged. At it the rotatory movements of the atlas on the axis 



