THE VERTEBRAL COLUMN. 119 
particular regions also present certain features in common, so that 
it is possible to classify them into cervical, thoracic, lumbar, sacral, 
and caudal groups. 
A typical vertebra—for the characters of which any one of the 

Fic. 56. Representative vertebrae: A, atlas, anterior surface; B, epistro 
pheus, lateral surface; C, fifth cervical vertebra, anterior surface; D, fourth 
dorsal, lateral surface; E, F, second lumbar vertebra, anterior and lateral 
surfaces. 
a.a., anterior arch of atlas; a.p., posterior arch of atlas; a.v., vertebral arch; 
c.v., vertebral body; d., dens epistrophei; f.a.a., anterior articular facet of 
epistropheus; f.a.s., superior articular pit of atlas; f.a.s.’, superior articular. 
facet of epistropheus; f.c.i., inferior costal demifacet for head of rib; f.c.s., 
superior costal demifacet; f.c.t., costal facet of transverse process; f.d., fovea 
dentis; f.i., intervertebral foramen; f.tr.,foramentransversarium; f.v., foramen 
vertebrale; 1., lamina of vertebral arch; m.]l., lateral mass of atlas; p.a., 
accessory process of lumbar vertebra; p.a.i., inferior articular process; p.a.s., 
superior articular process; p.m., mamillary process; p.s., spinous process; 
p.s.a., anterior spinous process; p.t., transverse process; p.t., triangular 
process; r., radix of vertebral arch; r.a., r.p., anterior and posterior radices of 
transverse process of cervical vertebra; t.a., t.p., anterior and posterior 
tubercles of atlas. 

thoracic or lumbar series may be taken (Fig. 56, D-F)—consists of a 
basal portion, the vertebral body (corpus vertebrae), and of a 
dorsal, vertebral arch (arcus vertebrae). The two portions 
