86 SKELETON. 



Of the Individual Lumbar Vertebra. 



These bones are not so well marked among themselves as the 

 other vertebrae. They may be distinguished in a single set, by 

 the successive increase in the size of their bodies. The first, 

 therefore, is known by its smallness; by the comparative short- 

 ness of its transverse process, and by the deep concavity between 

 the superior oblique processes. 



The transverse and spinous processes of the three middle 

 vertebrae are rather longer than those of the others; the third 

 has them the longest of all. The last lumbar vertebra may be 

 recognised by its greater size; by its body being flat, and deeper 

 in front than behind, so as to give it somewhat of a wedge shape; 

 by the greater size of its spinal foramen; by the obliquity back- 

 wards of the transverse process; and by the wide interval be- 

 tween the oblique processes, as well as by the lower of the lat- 

 ter facing almost directly forwards. 



Of the Pelvic Vertebrae. 



The os sacrum, (sacrum,) the largest by much of any of the 

 bones in the spinal column, has obtained its name from the sup- 

 position of its having been offered in sacrifice by the ancients.* 

 It forms the posterior and superior boundary of the pelvis, as 

 well as the pedestal of the spine, and may therefore be properly 

 studied along with either of them, though its association with 

 the spine seems more natural. In its lateral boundaries it is tri- 

 angular: it is also regularly concave before, and very irregularly 

 convex behind. 



In its forming state this bone consists of five pieces, separated 

 by long narrow interstices filled with cartilage. It is in this 

 condition that its pieces bear a very strong resemblance to the 

 true vertebra, and therefore have obtained the name of false 

 vertebrae. They are all fused into one by the progress and de- 

 velopment of the bone; but the marks of the original separation 

 remain, particularly on its front surface. 



Though the anterior face of the sacrum presents generally a 



* Portal. Anal. Med. vol. i. 345. 



