VERTEBRAL COLUMN. 299 



edge of the vertebra next in front, forms the 

 articular surface for the head of the rib. At 

 the posterior end are a similar pair of facets 

 for the ribs of the succeeding vertebra. 



ii. The neural arch is notched, both, in front and 

 behind, for the passage of the spinal nerves. 



iii. The transverse processes are short, stout, and 

 horizontal, and bear on their under surfaces 

 the articular facets for the tubercles of the 

 ribs. 



iv. The neural spine is long and slender, and slopes 

 obliquely backwards. 



v. The zygapophyses. The pre-zygapophyses face 

 upwards and outwards, the post-zygapo- 

 physes downwards and inwards. 



b. The posterior three or four thoracic vertebrae. 

 i. The centra are larger than in the anterior 

 thoracic vertebrae : the facet for the head of 

 each rib is confined to the anterior end of 

 the centrum, the posterior end having no 

 articular surface. 



ii. The neural spines are lower than in the anterior 

 vertebrae, but longer from before backwards. 



iii. The transverse processes are placed further 

 back, and have no articular facets for the 

 ribs. 



iv. Metapophyses appear in the ninth thoracic 

 vertebra, and increase considerably in size in 

 the succeeding ones. They are usually con- 

 fluent with the pre-zygapophyses in all except 

 the ninth thoracic vertebrae. 



The lumbar vertebrae. 



These are usually seven in number : the most 

 anterior one may, however, bear ribs, in which case 

 it is reckoned as a thirteenth thoracic vertebra, and 

 the lumbar vertebrae are then reduced to six. 



