VERTEBRAL COLUMN 105 



median wall of a deep notch. The cephalic articular surface occupies 

 the medial surface of the articular process. It is very slightly concave 

 dorso-ventrally, and faces toward the median line and the head, and 

 dorsally. The cephalic border on each side of the articular process 

 is sinuate ; from the median line laterally, first emarginate, and then 

 arcuate. It curves ventrally and toward the head into the upper part 

 of the cephalic border of the lateral mass. 



In the middle line of the dorsal surface are the three sacral 

 spinous processes. They are, as a rule, distinct from one another, 

 although occasionally their opposite edges may unite at their bases. 

 They are triangular and laterally compressed and point dorsally. 

 Their tips sometimes have a slight cephalic curve. Of the three, the 

 first is the largest and the third the smallest. 



On each side of the median line, opposite the intervals between the 

 spinous processes, are the tubercles formed by the united articular 

 processes. They vary much in size and in the degree of coalescence 

 of their elements. Cephalic and lateral to each tubercle is a dorsal 

 sacral foramen. These foramina are oval and of equal size, and placed, 

 like the caudal ventral foramina, obliquely. A groove, more or less 

 distinct, leads from the lateral end of each foramen in a cephalic and 

 lateral direction. 



The caudal articular processes or sacral cornua are small, but 

 prominent and distinct, They are directed toward the tail and but 

 slightly laterally and dorsally. They overhang the neural canal and 

 also the caudal intervertebral notches, which are large. The caudal 

 articular surfaces face ventrally and laterally. 



The lateral border of the dorsal surface is, in the cephalic part, the 

 somewhat irregular dorsal border of the lateral surface of the lateral 

 mass, caudal to which it is thin and emarginate. The caudal angles 

 are produced laterally and toward the tail. The caudal margin of the 

 dorsal surface is interrupted in the middle by the laminae carrying 

 the articular processes, at each side of which, on a lower level, it forms 

 the deeply emarginated caudal border of the inferior lateral angle. 



The part of the dorsal surface included between the spinous pro- 

 cesses and the line of free and coalesced articular processes is the 

 laminar part of the sacrum, and forms a strip wider in the cephalic 

 part than in the caudal part, and elevated above the rest of the dorsal 

 surface. It is convex from the median line laterally, and nearly flat 



