THE VERTEBRAL COLUMN. 287 



in the neck ; the dorsal carry the rihs ; the lumbar are found in 

 the region of the loins ; the sacral are united into one hony mass 

 called the sacrum, which supports to some extent the hind 

 Hmbs and the pelvic arch; the coccygeal form the tail-region. 

 A typical vertebra (fig. 149) consists of a solid lower portion, the 

 centrum (1 and 2), and an upper bony arch, the neural arch (4), 

 in which lies the spinal cord. At the point where the two 

 halves of the neural arch meet there springs a bony spine more 

 or less developed, the dorsal or neural spine (fig. 149, 3). On 

 each side of the neural arch a process juts out, the zygapophysis 



Fig. 149. — Lumbab Vebtebba. (Front view.) 



1, Centrum ; 2, its facet ; 3, dorsal spine ; 4, spinal foramen ; 5, anterior articulat- 

 ing process ; 6, transverse process ; 7, posterior articnlating process, (Cliaavean.) 



(5 and 7). From the sides of the vertebrse there also project a 

 lateral process on each side, called the transvei'se process (6). 



Theoretically there is another arch below the centrum, the 

 so-called haemal arch, which protects the blood-system. But 

 this can only be recognised in some animals, unless we take 

 the ribs as partly forming the arch. It is best seen in the 

 caudal vertebra of some fish. The vertebrae unite together partly 

 by their centra and partly by the zygapophyses. When a 

 vertebra has both faces of the centrum scooped out it is called 

 an amphicoslous vertebra ; when one end (the anterior) is pro- 

 jecting and the posterior concave, it is termed qpisthocoelozis / 

 when concave in front and convex behind, procaelous. 



In the horse the cervical vertebrae wiU be seen to be seven in 



