THE RABBIT. 267 



25. The second cervical vertebra, or axis ; the centrum 

 is produced anteriorly into a strong, bluntly-pointed peg, 

 the odontoid process ; on the under surface of this is 

 an articular surface, and on each side of its base is another 

 large surface ; all these are for articulation with the first 

 vertebra ; the spine is flattened from side to side, and greatly 

 produced from before backwards ; the transverse processes 

 are small, directed backwards, and perforated by the verte- 

 brarterial canal. In young rabbits (six weeks) this axis 

 consists of three pieces, one forming the arch, another the 

 posterior part of the centrum, and the third the anterior 

 part of the centrum with the odontoid process : the latter 

 ossification (OS odontoideum) answers to part of the 

 centrum of the atlas. 



26. The first cervical vertebra or atlas : the centrum 

 is reduced to a mere flat plate, hardly thicker than the arch, 

 and with less than half the antero-posterior dimensions of 

 the latter ; the transverse processes are large, flattened from 

 above downwards, and perforated ; just within and below 

 the vertebrarterial canal, on the posterior face of the 

 vertebra, is a large oval facet for articulation with the 

 corresponding surface of the axis, and on the upper sur- 

 face of the centrum is a smaller facet corresponding to the 

 surface on the ventral face of the odontoid ; on the anterior 

 surface are large, paired, irregularly crescentic facets for the 

 occipital condyles (§ 34). 



27. In an entire skeleton note the mode of articulation 

 of the vertebrae : the centra are united by pads of fibro- 

 cartilage, the intervertebral ligaments, only to be seen 

 in the fresh state ; the arches are united by the anterior 

 zygapophysis of any vertebra being overlapped by the 

 posterior zygapophysis of the vertebra next in front. 



28. The intervertebral foramina, seen in the entire 



