A DORSAL VEKTEBKA 



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twelve pairs of ribs. This is called the dorsal region. 

 The remaining five are very large and are called the lum- 

 bar vertebrae. Together they make up the lumbar or 

 loin region. Below these lumbar vertebrae is a single large 

 bone called the sacrum. This is actually composed of 

 five vertebrae, separate in the young child but fused in the 

 adult. On the end of this sacrum is a curved tip of bone 

 (the coccyx) formed of four separate bones fused together. 

 (For regions, see Fig. 84.) 



Structure of the vertebrae. — (See Ex. XLIX., c.) The 

 vertebrae are all irregular bones with a central portion 

 called the body, and many projections or processes. The 

 first two cervical vertebrae are formed for a special purpose 

 and are called the atlas and axis. The remaining verte- 

 brae have the same general form, differing only in size. 

 We shall first consider a typical vertebra and then note 

 the variations in the other forms. 



A dorsal vertebra. — Viewed from above (see Fig. 85), 



Fia. 85 — Dorsal vertebra; A^ top view; B, side view; 1, centrum; 2, neural 

 cavity ; 3, spinous process ; 4, transverse processes. 



it shows the following regions: First, a central mass of 

 bone called the body, or centrum, which, in the human 

 body, extends toward the ventral side. From this on each 

 side an arch of bone curves backward inclosing a cen- 



EDDT. PHTS. — 15. 



