THE BONES. 



sacral vertebrae, which together constitute what is called the sacral or supersacral 

 spine. These processes are united at their base only, and remain isolated for the 

 remainder of their extent ; they all incline backwards 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 super-sacral Jara- 

 raina. These orifices open into the spinal canal, and communicate with four 

 analogous, but wider apertures, pierced at the inferior face of the bone, and for 



this reason named the sub-sacral 

 Fig- 25. foramina. The inferior face is 



smooth, and shows traces of the 

 N^L ,m^''''. J^S&^fi^ ^^^ '''•■' primitive separation of the vertebral 



^^■-^'"^^^P^^^^^^^i^m S^ V bodies ; the sub-sacral foramina, 



~ ' ' ^ which represent, with the corre- 



sponding super-sacral openings, the 

 intervertebral foramina of the other 

 regions of the spine, are observed 

 on this surface. 



Borders. — The hvo borders, thick 

 and concave, form, posteriorly, a 

 rugged lip ; in front, they present 

 an irregular surface inclining ob- 

 liquely 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. 



Siimmit. — 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. 



The sacrum of the Ass much resembles that of the Horse ; nevertheless, it is 

 possible to distinguish it by the shape of the articular tubercles of the first sacral 

 vertebrae, which resemble those of the articular tubercles of the lumbar region, 

 and the traces those tubercles have left between the sacral vertebra3, especially 

 between the first. 



LATERAL VIEW OF SACRUM. 



1, Articular surface of body ; 2, 3, articular surfaces 

 corresponding to those on the transverse processes 

 of the last lumbar vertebra; 4, spinal foramen; 5, 

 auricular facet; 6, anterior articular processes; 

 7, inferior or sub-sacral foramina ; 8, superior 

 spinous processes ; 9, summit or coccygeal ex- 

 tremity. 



Differential Characters in the Sacral Vertebra op other Animals. 



A. Ox. — The sacrum of the Ox is more voluminous and curved than that of the Horse 

 The spinous processes are entirely consolidated, and are surmounted by a thick rugged lip ; 



