THE SACRUM. 93 



part of the spinal column. The vertebrae gradually 

 increase in size from the axis to the first dorsal, then 

 decrease to the fifth dorsal, and then increase in size from 

 the fifth dorsal to the fifth lumbar. The intervertebral 

 foramina are largest in the lumbar, next in the cervical, 

 and smallest in the dorsal region. 



THE SACRUM. 



The sacrum is a wedge-shaped bone, which sets be- 

 tween the two ossa innominata. It presents for exam- 



frtmtnttry 



FIG. 42. THE SACRUM, ANTERIOR SURFACE. 



ination a base, an apex, two lateral borders, and an 

 anterior and posterior surface. The base presents 

 upward, and supports the spinal column. The apex, 

 directed downward, articulates with the coccyx. The 

 lateral borders articulate with the ossa innominata. The 

 bone is flattened antero-posteriorly, and strongly curved. 

 The anterior surface is smooth, markedly concave from 

 above downward, slightly so from side to side. About 

 an inch on either side of the median line are the four 



