104 



MAMMALIAN ANATOMY 



and faces laterally, toward the tail, and slightly dorsally. An ear- 

 shaped auricular 1 articular facet, which occupies its caudal and ventral 

 half, joins a facet on the cephalic part of the inner surface of the 

 innominate bone. The remainder of the surface, lying cephalic and 

 dorsal to the auricular surface, is excavated and roughened, and fur- 

 nishes attachment to strong sacro-iliac interosseous ligaments. The 

 caudal half of the lateral surface is little more than a border limiting 



o 



the dorsal and ventral surfaces of the united transverse processes. As 

 a surface, it is straight in the cephalic part, but curves laterally as well 

 as toward the tail. 



The dorsal surface (Fig. 76) of the sacrum has the same general 

 outline as the ventral surface, but is not so wide in the cephalic part. 



FIG. 76. 



Cephalic Articular Process. 



Lateral Mass. 



Auricular Surface, 

 with Ilium. 



A Sacral Spine. 



A Transverse Process. 



United Articular Processes. 

 United Transverse Processes. 



A Dorsal Sacral Foramen. 



Catidal Articular Process. 



Caudal Intervertebral Notch. 



THE SACRUM, DORSAL ASPECT. 



It is composed of the dorsal surfaces of the united laminae and trans- 

 verse processes of the constituent vertebra. 



The cephalic border presents a considerable median emargination, 

 at each side of which are the prominent cephalic articular processes. 

 Each process is directed laterally, dorsally, and toward the head 

 beyond the lateral masses of the body. It is compressed from side 

 to side, and is as high as it is long. Its lateral surface is convex 

 from the cephalic to the caudal edge and concave in a dorso-ventral 

 line, and forms, when the sacrum and the innominate are united, the 



1 From auricula, a little ear. 



