THE VERTEBRAL COLUMN 51 



lumbar region. This constitutes an arch between the attachments 

 to the fore and hind Hmbs for the support of the body in a Hght 

 medium when the Hmbs raise it from the ground. The anterior and 

 posterior ends of the body, which project beyond the supporting 

 limbs, are sustained by the column curving ventrad in the cervical 

 and caudal regions (with, of course, stout ligaments dorsally). In 

 man, the curvatures are modified in relation to the assumption of 

 an erect attitude, a lumbar curve ventrad developing to counteract 

 the dorsal curve of the thoracic region, and the caudal region is 

 reduced to a vestige, the coccyx, consisting of coalesced vertebrae. 





■»' /„, «'. ^^\ S 





Fig. 27. Mid-lumbar vertebrae of bear (A, fifth), rabbit (B, fifth), and 

 man (C, third): a, inferior articular process; c, body; m, mamillary and superior 

 articular process; s, spinous process; t, transverse process. 



The individual vertebra is made up of a massive ventral body, 

 or centrum, and a dorsal arch, both composed of replacing bone 

 (Fig. 28). Both body and arch bear processes which extend into 

 the surrounding muscles and serve for their attachment. The 

 principal processes are dorsomedian or spinous, lateral or trans- 

 verse, and in the lumbar region, dorsolateral or mamillary. Less 

 prominent processes bearing surfaces for mutual articulation are 

 also present. 



Generally speaking every vertebra has three principal functions 

 — to support the body, to protect the spinal cord, and to provide 

 a basis of attachment for muscles. In the support and movement 

 of the body, the ventral part of the vertebra is subjected mainly to 

 forces compressing it, the dorsal part to forces of tension. Hence 



