THE VERTEBRAL COLUMN. 



versely oval articular facet (the cranial end of the centrum of 

 the first sacral vertebra), for articulation with the centrum of 

 the last lumbar vertebra. Dorsad of this is the sacral canal, 

 more depressed than the vertebral arch craniad of it. It sup- 

 ports a spinous process (Fig. 6, a) which is directed dorsad. 

 At the junction of its lamina and radix is seen the prominent 



FIG. 6. SACRUM, DORSAL SURFACE. FIG. 7. SACRUM, VENTRAL SURFACE. 



Fig. 6. i, 2, 3, the three sacral vertebrae, a, ', spinous processes; b, cranial 

 articular process of first sacral vertebra; f, expanded transverse process of first 

 sacral vetebra; el, caudal articular processes of third sacral vertebra; e, transverse 

 processes of third sacral vertebra; f, tubercles formed by fused articular processes 

 of the vertebrae; g, dorsal (or posterior) sacral foramina. 



Fig. 7. i, 2, 3, the three sacral vertebrae, a, the transverse ridges formed by 

 the union of the centra; ^, cranial articular processes of first vertebra; c, transverse 

 process of first vertebra; d> caudal articular processes of third vertebra; e, trans- 

 verse processes of third sacral vertebra; /,_/"', ventral (or anterior) sacral foramina; 

 g, notch which helps to form third ventral sacral foramen. 



cranial articular process (b} with sometimes slight indications 

 of a mammillary process on its lateral surface. Laterad of the 

 articular facet is seen the cranial face of the expanded " pseudo- 

 transverse process ' ' (c) of the first sacral vertebra. The 

 ventral border of the base is concave ventrad, forming an arc 

 of about 1 20 degrees. The apex shows the caudal end of the 

 last sacral centrum. Dorsad of this are the vertebral arch with 

 a very short spinous process (a'}, and the caudal articular 

 processes (d}. Laterad of the centrum appears the laterally 

 directed thin transverse process (e). 



The ventral or pelvic surface (Fig. 7) is smooth, concave 

 craniad, convex caudad, and crossed by two transverse ridges 

 (a) along which are seen the ossified remains of the interverte- 

 bral fibro-cartilages. At the ends of the first ridge is a pair of 

 nearly circular ventral (or anterior) sacral foramina (/) for 



