CHAP, in.j SKELETON OF THE HEAD AND TRUNK. 



The convexity outside the prezygapophysis is at its maximum in 

 the fourth vertebra. It is really a rudimentary metapophysis. 



The neural lamina of the sixth and seventh vertehrse show a 

 ridge-like process on the inner side of each postzygapophysis. This 

 is called a hyperapophysis. 



9. The second cervical vertebra, termed the AXIS, differs con- 

 spicuously from every other bone of the spine in having a large blunt 



Fig. 21. THE ATLAS VERTEBRA. 



A. Side view. 



B. Front view. 

 . Back view. 

 D. Dorsal view. 

 . Ventral view. 



/. Foramina. 



ii. Neural lamina. 



s. Rudiment of neural spine. 



t. Transverse process. 



z. Articular surfaces. 



y. Hypapophysial tubercle. 



process of bone (like a tooth or peg, o), extending forwards from 

 the anterior portion of the centrum on which account the bone is 

 sometimes termed the vertebra dcntata. This eminence is called the 

 odontoid process. It presents a smooth articular surface below, and 

 a smooth groove above. The lower surface of the rest of the 

 centrum of the axis exhibits a median hypapophysial prominence 

 or ridge. The pedicle has a very deep anterior notch, beneath 

 which is an anterior lateral articular surface (al), instead of a pre- 

 zygapophysis. The neural spine (s) is merely an _ elongated ridge 

 extending along the summit of the stout neural lamina). 



The postzygapophyses (s) exist as usual, but the prezygapo- 

 physes are, as has just been said, absent. There is however instead, 

 on each side, the just mentioned large articular surface (at), looking 

 forwards and outwards, and supported on the centrum, beside but 

 behind the odontoid process. The transverse process (t) is short, 

 pointed, perforated, and backwardly projecting from near 

 hinder end of the side of the centrum. 



