vi-:nri-:nnAL COLI:M\. 



ii 



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



is ..ftcn bitid; their length diminishes fr.nn tin'- second to th(; iii'lh Lone. 



i >n each side, of tho sacral spine 



( \ist.s a groove, at tho bottom . Fig. 17. 



of which uro four openings the 



- rsacral foramina. Those 

 ontiees open into tho spinal 

 canal, and communicate with 

 four analogous, but wider aj>er- 

 tur- 'I at the inferior 



of the bone, and for this 

 reason named tho subsacral fo- 

 rd in inn. Tho inferior face is 

 smooth, and shows traces of the 

 primitive separation of tho ver- 

 tebral bodies ; the subsacral fo- 

 nuuiua, which represent, with 

 the corresponding supersacral 

 openings, the intervertebral fo- 

 ramina of tho other regions of 

 the spine, are observed on this 

 surface. 



Borders. Tho two lorders, 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, tho 

 superior, serves for ligamentous insertions. 



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

 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, tho articular 

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

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

 processes of the last lumbar vertebra. 



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

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

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

 notches of that vertebra. 



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

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

 from before to behind. 



LATKUAl. VIi:\V OF SA< IM.M. 



Articular surface of bo<ly ; 2, 3, Articular surfaces 



on-responding to those on the transverse processes 



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



Auricular facet; 6, Anterior articular pi. 



7, Inferior or subsacral foramina ; 8, Superior 



spinmis processes; 9, Summit or coccygeal es- 



tremitv. 



5. Coccygeal Vertebra. 



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

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

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

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

 transverse processes, looking backwards ; tho articular processes only are 

 altogether absent. In the succeeding vertebno, these diameters become 

 effaced; tho vertebral lamina) do not join completely, and the spinal canal 

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



