THE VERTEBRAL COLUMN. 317 



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

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

 called the " sacrum," which supports to some extent the hind 

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

 A typical vertebra (fig. 182) 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 dmsal or neural spine (fig. 182, 3). On 

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



Fio. 182.— Lumbar Vehtebra (Front view.) 



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

 ing process ; 6, transverse process ; 7, posterior articulating process (Chauveau.) 



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

 lateral process on each side, called the transverse process (6). 



Theoretically there is another arch below the centrum, the 

 so-called hfemal arch, whicli 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 zygapojihyses. When a 

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

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

 jecting and the posterior concave, it is termed opiisthoccelcnis ; 

 when concave in front and convex behind, procoslous. 



In the horse the cervical vertebras are seven in number. 



