220 THE VERTEBRATE SKELETON. 



The inferior arch is a short irregular bone bearing two 

 converging facets for articulation with the occipital condyle 

 and odontoid process respectively. 



The centrum or odontoid process has a convex anterior 

 surface for articulation with the neural and inferior arches, 

 and a concave posterior surface by which it is united with 

 the centrum of the second or axis vertebra. It bears pos- 

 teriorly a small epiphysis which is really a detached portion of 

 the inferior arch. 



The second or axis and following five cervical vertebrae, 

 though showing distinct differences, resemble one another con- 

 siderably, each having a fairly elongated centrum with a keel- 

 like hypapophysis, each having also a neural arch with 

 prominent articulating surfaces, the anterior of which, or 

 prezygapophyses, look upwards and inwards, while the 

 posterior ones, the postzygapophyses, look downwards and 

 outwards. They however, as was previously mentioned, differ 

 very remarkably in the character of the articulating surfaces 

 of the centra. Thus the second and third vertebrae are 

 convex in front and concave behind, the fourth is biconvex, 

 the fifth is concave in front and convex behind. The sixth 

 is concave in front and attached to the seventh by a flat 

 surface behind, the seventh has a flat anterior face and two 

 slightly convex facets behind. The vertebrae all have short 

 blunt transverse processes and the second has a prominent 

 neural spine. 



The eighth cervical vertebra is curiously modified, the 

 centrum is very short, has a rather prominent hypapophysis, 

 and is convex behind, while in front it articulates with the 

 preceding centrum by two concave surfaces. The neural arch 

 is deeply notched in front and bears two upwardly-directed 

 prezygapophyses, while behind it is very massive and is drawn 

 out far beyond the centrum, bearing a pair of flat postzyga- 

 pophyses. The top of the neural arch almost or quite meets 

 a blunt outgrowth from the nuchal plate. 



