Bones of the Spine. 



Processus articularis superior 



73 



Tuberositas 

 sacralis 



Fades 

 auricularis 



Crista sacralis 

 lateralis 



_ Crista sacralis 



articularis 

 Crista sacralis media 



[ Foramen sacrale posterius 



~-- Hiatus sacralis 

 Cornu sacrale 



Apex ossis sacri 



91. Sacrum, OS Sacrum, from behind and above. 



The facies dorsalis ossis sacri is very rough and convex from above downward. On 

 it five rows of processes and projections run downward, almost parallel to one another. The 

 middle row, crista sacralis media, has resulted from the fusion of the processus spinosi and 

 is most marked; it presents often an uninterrupted ridge, hut is frequently incomplete. Lateral- 

 ward on each side lies the crista sacralis articularis ; it is to he considered as the processus 

 articulares fused with one another and usually projects only moderately above the surface. 

 Lateralward from this, separated from it by the foramina sacralia posteriora, is the crista 

 sacralis lateralis ; it arises from the fusion of the processus transversi and is usually more 

 distinctly marked than the crista sacralis articularis. The four foramina sacralia posteriora 

 like the anterior, are situated on both sides in nearly parallel rows ; they lead (see Fig. 92 a ) 

 forward and medianward into the canalis sacralis, forward and downward to the foramina 

 sacralia anteriora. 



Corresponding to the upper end of the cristae sacrales articulares two completely deve- 

 loped processus articulares superiores pass vertically upward ; their facies articulares superiores 

 are directed medianward and backward and articulate with the processus articulares inferiores 

 of the fifth lumbar vertebra. From the lower end of the cristae sacrales articulares the two 

 small cornua sacralia pass downward to meet the comua coccygea ossis coccygis. Median- 

 ward from them lies the lower opening of the canalis sacralis, hiatus sacralis; it is usually 

 triangular and varies much in size. 



