CHAP. in. J SKELETON OF THE HEAD AND TRUNK. 



43 



The convexity outside the prezygapophysis is at its maximum in 

 the fourth vertebra. It is really a rudimentary mctapophysis. 



The neural laminas of the sixth and seventh vertebra? show a 

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

 is called a ]ujpera])ophi/sis. 



§ 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.— Tbe Atlas Vertebra. 



A. Side view. 



B. Front view. 



C. Back view. 



D. Dorsal \'iew. 

 £. Ventral view. 



/. Foramiua. 



■n. 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 dentata. 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 the 

 hinder end of the side of the centrum. 



