10 THE BONES. 



sacral vertebrae, which together constitute what is called the sa^al 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 fora- 

 mina. 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 

 primitive separation of the vertebral 

 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 two borders, thick 

 LATERAL VIEW OF sACKtJM, and coucavc, form, posteriorly, a 



1, Articular surface of body ; 2, 3, articular surfaces rUO"ged lip ; in frout, they present 

 correspondiner to those ou the tiansverse processes • i e • ^• ' \. 



ofthe last lumbar vertebra; 4, spinal foramea; 5, ^U irregular SUrfaCC mclmmg ob- 



auricular facet; 6, anterior articular i)rocesses ; liqucly frOm above tO bcloW, from 



7, inferior or sub-sacral foramina; 8, superior ^^jthiu OUtwards, and from before 

 spinous processes; y, summit or coccygeal ex- i • i mi i • i • 



tremity. to behmd. 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 sacrmn ; 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 

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

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

 between the first. 



Differential Characters in the Sacral Vertebra of 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 ; 



