THE VEBTEBBAL COLUMN. 



27 



Fig. 17, 



and terminate, with the exception of the first, by a tuberous summit, which 

 is often bifid ; their length diminishes from the second to the fifth bone. 

 On each side of the sacral spine 

 exists a groove, at the bottom 

 of which are four openings — the 

 supersacral foramina. These 

 orifices open into the spinal 

 canal, and communicate with 

 four analogous, but wider aper- 

 tures, pierced at the inferior 

 face of the bone, and for this 

 reason named the subsacral fo- 

 ramina. The inferior face is 

 smooth, and shows traces of the 

 primitive separation of the ver- 

 tebral bodies ; the subsacral fo- 

 ramina, which represent, with 

 the corresponding supersacral 

 openings, the intervertebral fo- 

 ramina of the other regions of 

 the spine, are observed on this 

 surface. 



Borders. — The two horders, thick and concave, form, posteriorly, a rugged 

 lip ; in front, they present an irregular surface inclining obliquely from 

 above to below, from within outwards, and from before to behind. This 

 surface, which is intended for the articulation of the sacrum with the ossa 

 innominata, is divided into two parts : one, the inferior, named in man the 

 auricular facet, is slightly undulated and diarthrodial ; the other, the 

 superior, serves for ligamentous insertions. 



Base. — This offers : 1, On the median line, the anterior orifice of the 

 sacral canal, and the anterior articular surface of the body of the first sacral 

 vertebra, which is oval and slightly convex ; 2, On the borders, the articular 

 processes and anterior notches of this vertebra, as well as the elliptical 

 and somewhat convex facets which bring it into contact with the transverse 

 processes of the last lumbar vertebra. 



Summit. — The summit, thrown back, presents : 1, The posterior orifice 

 of the sacral canal ; 2, The posterior articular surface of the body of the 

 last sacral vertebra ; 3, The vestiges of the articular processes and posterior 

 notches of that vertebra. 



Sacral canal. — This is the portion of the spinal canal which is 

 channeled out of the sacrum ; it is triangular, and diminishes in width 

 from before to behind. 



LATERAL VIEW OF SACKDM. 

 1, Articular surface of body : 2, 3, Articular surfaces 

 corresponding to those on the transverse processes 

 of last lumbar vertebra; 4, Spinal foramen; 5, 

 Auricular facet ; 6, Anterior articular processes ; 

 7, Inferior or subsacral foramina ; 8, Superior 

 spinous processes ; 9, Summit or coccygeal ex- 

 tremity. 



5. Coccygeal Vertcbrce. 

 The coccygeal region, or coccyx, comprises from fifteen to eighteen de- 

 generate vertebrae, which gradually diminish from the first to the last. In 

 the first three or four, nearly all the characteristics of true vertebra are 

 found; they show a spinal foramen, a body, a spinous process, and 

 transverse processes, looking backwards ; the articular processes only are 

 altogether absent. In the succeeding vertebra, these characters become 

 effaced ; the vertebral laminae do not join completely, and the spinal canal 

 is only a simple groove, which, gradually decreasing in depth, at last 



