26 ANATOMY OF THE RAT 



with the occipital condyles of the skull by means of two 

 lateral concave surfaces, the superior articular foveae, one 

 on each side. It bears posteriorly a pair of lateral ovoid 

 surfaces, inferior articular foveae, for articulation with 

 the epistropheus. A third articular surface connects these 

 facets ventrally. In man, and presumably in the rat, the 

 chief movement permitted between the superior articular 

 foveae and the occipital condyles is a *' nodding" of the 

 head. In ''shaking" the head the atlas revolves around 

 the dens as a pivot. The elongated transverse process 

 of the atlas is flattened dorsoventrally. Its dorsal surface 

 slopes backward to the posterior end of the vertebra, where 

 it joins a vertical plate. Between this plate and the in- 

 ferior articular fovea is the posterior opening of the fora- 

 men transversarium, through which the vertebral artery 

 passes. This foramen extends anterodorsally, and com- 

 municates with the dorsal surface of the atlas by an oval 

 opening. The artery then turning medially traverses the 

 atlantal foramen to the inner surface of the atlas. 



The centrum of the epistropheus is flattened dorsoven- 

 trally and prolonged anteriorly by the dens. The dens 

 articulate with the fovea dentis by the anterior articular 

 facet on its ventral side. The cranial articular facets, one 

 on each side of the epistropheus, impinge upon the inferior 

 articular foveae of the atlas. The postzygapophyses, one 

 toward the upper end of each pedicle, articulate behind 

 with the prezygapophyses of the third cervical vertebrae. 

 The laterally flattened neural spine is considerably higher 

 than that of any other cervical vertebra. It extends for- 

 ward over the atlas and backward over the third vertebra. 

 The foramen transversarium pierces the base of the short 

 transverse process. 



In the fifth cervical vertebra the centrum and vertebral 

 arch form in side view an obtuse angle with each other. 



