SKELETON AND TEETH 69 



upon the neural arch. From the summit of the arch arises 

 the neural spine, a more or less nearly straight rod or plate of 

 bone, which may be enormously long or extremely short, 

 massive or slender, in accordance with the muscular attach- 

 ments which must be provided for. Finally, should be men- 

 tioned the transverse processes, rod-like or 

 plate-like projections of bone, which arise, 

 one on each side of the vertebra, usually 

 from the centrum, less commonly from the 

 neural arch ; these also differ greatly in form 

 and size in the various regions of the column. 

 Anatomists distinguish several other pro- ^^ ^^ — Firat dorsal 

 cesses of the vertebra, but for our purpose vertebra of Woif 



■ , • , J. J. 1 j.i_ -J. from the front, en., 



it IS not necessary to take these mto con- centrum, r. facet 



sideration. ^°r ^^^ l^ead of the 



Five different regions of the backbone "he tube'rcinf the 



may be distinguished, in each of which the "''• *''■■ transverse 



,•■• process, pr.z., ante- 



vertebrse are modined in a characteristic nor zygapophyses. 

 way. There is (1) the cervical region, or "■*^' ^^^'^^^ spine, 

 neck, the vertebrae of which, among mammals (with only one 

 or two exceptions) are always seven in number, however long 

 or short the neck may be; the immoderately long neck of 

 the Giraffe has no more and the almost invisible neck of 

 the Whale has no less, and thus the elongation of the neck 

 is accomplished by lengthening the individual vertebrae and 

 not by increasing their number. (2) Those vertebrae to 

 which ribs are attached are named dorsal or thoracic and 

 can always be recognized by the pits or articular facets 

 which receive the heads of the ribs. (3) Behind the dorsal 

 is the lumbar region, or that of the loins, made up of a num- 

 ber of vertebrae which carry no ribs. The dorso-lumbars are 

 known collectively as the trunk-vertebrce and are generally 

 quite constant in number for a given group of mammals, though 

 often differently divided between the two regions in different 

 members of the same group. In the Artiodactyla, for example, 



