THE VERTEBRAL COLUMN. 9 
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, 2) which is directed dorsad. 
At the junction of its lamina and radix is seen the prominent 
Fic. 6.—Sacrum, Dorsa SuRFACE. Fic. 7.—SACRUM, VENTRAL SURFACE. 
Fig. 6.—1, 2, 3, the three sacral vertebrae. «, a’, spinous processes; 4, cranial 
articular process of first sacral vertebra; ¢, expanded transverse process of first 
sacral vetebra; d@, caudal articular processes of third sacral vertebra; ¢, transverse 
processes of third sacral vertebra; 7, tubercles formed by fused articular processes 
of the vertebrze; g, dorsal (or posterior) sacral foramina. 
Fig. 7.1, 2, 3, the three sacral vertebrae. a, the transverse ridges formed by 
the union of the centra; 4, cranial articular processes of first vertebra; c, transverse 
process of first vertebra; @, caudal articular processes of third vertebra; ¢, trans- 
verse processes of third sacral vertebra; 7, 7’, ventral (or anterior) sacral foramina; 
g, notch which helps to form third ventral sacral foramen. 
cranial articular process (4) 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 120 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 (@’), and the caudal articular 
processes (@:). Laterad of the centrum appears the laterally 
directed thin transverse process (¢). 
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 
