498 



THE RABBIT 



natural position, an intervertebral foramen is formed for the passage 

 of a spinal nerve. The roof of the arch is continued into a long 

 neural spine (n. sp) projecting upwards and backwards, and just 

 above the intervertebral notches are a pair of anterior and posterior 

 articular processes or zygapophyses (pr. z, pt. z), which articulate 

 synovially with the vertebrae next in front and behind respectively. 

 The articular surface of each pre-zygapophysis looks upwards and out- 

 wards, that of the post-zygapophysis downwards and inwards. Arising 



laterally from either side of 

 the arch is an outstanding 

 transverse process (t. pr), on 

 the under surface of which is 

 an articular tubercular facet, 

 (t. f) with which the upper 

 fork of the rib (p. 500) arti- 

 culates. The lower fork or 

 head of the rib articulates 

 with a facet (c. f) formed 

 partly by the anterior edge of 

 the corresponding centrum 

 just at the base of the neural 



4 . Fifth thoracic vertebra of the arch, and partly by the pcs- 

 rabbit, from the left side ( x i^). terior edp-e of the centrum 



c. centrum ; c.f. capitular half-facet for fifth, 



and c.f". for sixth rib ; ep. epiphysis ; next in front, SO that each 

 i. v. n. intervertebral notch ; n. a. neural , ir 



arch ; n.sfi. neural spine ; pr.z. pre-zyga- centrum bears half a capltu- 

 pophysis ; ft. z post-zygapophysis ; t.f. far facet, &$ it is called, on 

 tubercular facet for fifth rib; t.pr. trans- 

 verse process. either side, both anteriorly 



and posteriorly (c. f , c. f"). 



There are no free ribs in the vertebrae of other regions, in which, 

 however, they are represented in the embryo, but early fuse with the 

 corresponding transverse processes. 



The first cervical vertebra, or atlas, is ring-shaped, and its lower 

 portion is narrow and unlike the other centra. The neural spine is 

 small, and the transverse processes are broad horizontal plates, each 

 perforated at its base by a vertebrarterial canal, through which the 

 vertebral artery runs. On the anterior face of the lateral parts of the 

 atlas are two concave articular facets for articulation with the occipital 

 condyles of the skull, and on its posterior face are two smaller facets for 

 articulation with the second vertebra. The second cervical vertebra, or 



