THE LIZARD. 133 



the convex posterior face of the centrum next in front, 

 while its anterior zygapophyses are overlapped by the pos- 

 terior zygapophyses of the preceding vertebra. 



12. The intervertebral foramina, spaces between the 

 neural arches of successive vertebrse, due to the fact that 

 each neurapophysis is notched, slightly in front, more deeply 

 behind. 



13. The cervical vertebrae, with the exception of the 

 first two, resemble the thoracic in essential respects, but are 

 proportionally shorter from before backwards. 



14. A sub-vertebral wedge-bone (autogenous hy- 

 papophysis) is developed in connection with the ventral 

 face of the centrum of the third cervical vertebra at its 

 anterior end : it forms a small downwardly directed process, 

 its anterior face furnishing part of the concave anterior 

 surface of the vertebra. 



15. The second cervical vertebra or axis, distinguished 

 by the short conical odontoid process projecting forwards 

 from the anterior face of its centrum, and constituting 

 a separate ossification or OS odontoideum. The axis, 

 like the succeeding vertebra, has a sub-vertebral wedge-bone. 



1 6. The atlas, or first cervical vertebra, a ring-like bone, 

 consisting of three separate ossifications, one ventral, re- 

 presenting part of the centrum, the others dorso-lateral, 

 representing separate neurapophyses : between the latter 

 stretches, in the fresh state, a transverse horizontal ligament, 

 the space above which represents the neural arch of the 

 atlas, while between it and the ventral ossification fits the 

 odontoid bone, representing the dorsal portion of the 

 centrum of the atlas. The anterior face of the atlas presents, 

 ventrally, a smooth articular facet for the occipital . condyle 

 of the skull (§ 31). 



17. The posterior thoracico-lumbar vertebrae differ but 



