VERTEBRAL COLUMN 



101 



The First Sacral differs from the two which follow by its superior 

 size, by the large lateral masses, and by the very prominent cephalic 

 articular processes. 



The Second Sacral differs from the third by its superior size and 

 by showing the marks of bony union at each end. 



The Third Sacral differs from the second and first by its inferior 

 size and by the caudal and lateral direction of the caudal end of the 

 transverse processes. 



THE SACRUM. 



General Description. The Sacrum is irregularly rectangular, 

 wider and higher at the cephalic end than at the caudal end. Its 

 cephalo-caudal diameter, which about equals the maximum cephalo- 

 caudal diameter of the seventh lumbar vertebra, is an eighth greater 

 than its greatest transverse width at the cephalic end. The maximum 

 dorso-ventral height is a third less than the maximum cephalo-caudal 



FIG. 72. 



Cephalic Articular Process. 



Ala. 



First Sacral Vertebra. 



Lateral Mass. 



Second Sacral Vertebra. 



Ventral Sacral Foramen. 



TJtird Sacral Vertebra. 



Caudal. Articular Surface. 



Ti-ansverse Process. 



\lntervertebral Notch. 



THE SACRUM, VENTRAL ASPECT. 



diameter. In the ordinary position in walking, the cephalic end of the 

 sacrum has a greater dorso-ventral diameter than the caudal end. 



The outline of the ventral surface (Fig. 72) of the sacrum is 

 rhomboidal. The cephalic third of the surface is twice as wide trans- 

 versely as the caudal two-thirds, except where the caudal angles are 

 produced laterally and toward the tail. Each lateral margin is, in its 

 cephalic third, sharp, prominent, arcuate in a cephalo-caudal line, and 



