124 Anatomy of the Rabbit. 



region as small elevations of the transverse processes. Each of the 

 first three of the lumbar vertebrae bears a median ventral pro- 

 jection, the anterior spinous process (processus spinosus anterior), 

 for the attachment of the lumbar portion of the diaphragm. 



The sacral vertebrae (vertebrae sacrales) are four in number. 

 In contrast to the true vertebrae — those united by ligament and 

 articular surfaces — of the remaining portions of the vertebral 

 column, they are false vertebrae, united in the young by synchon- 

 droses, and in the adult coalesced to form a composite structure, the 

 OS sacrum (Fig. 57). The axis of the sacrum forms an obtuse 

 angle with that of the lumbar vertebrae, the angle being indicated 

 by a ventral projection, the promontory (promontorium), formed 

 by the last lumbar and first sacral vertebrae. The sacrum is the 

 medium through which the vertebral column — in other words, the 

 posterior portion of the trunk — is supported on the posterior limbs. 

 Its anterior dorsal portion bears on either side a roughened area, 

 the auricular surface (fades auricularis), for articulation with 

 the pelvic girdle. This surface is borne for the most part on the 

 transverse process of the first sacral vertebra. 



The sacrum exhibits many features resulting from its formation 

 through the fusion of originally distinct vertebrae. On the ventral, 

 or pelvic surface (fades pelvina), the lines of junction may be 

 traced either between the bodies, or between the transverse pro- 

 cesses. Four pairs of apertures on this surface, the anterior sacral 

 foramina (foramina sacralia anteriora), lead into the intervertebral 

 foramina, and give passage to the sacral spinal nerves. On the 

 dorsal surface (fades dorsalis) a pair of posterior sacral foramina 

 lie in the line of junction of the first and second vertebrae. The 

 spinous processes are evident in all four vertebrae. The combined 

 articular and mamillary processes are conspicuous only in the 

 first two, but are represented in the succeeding two by low, rough- 

 ened tubercles. In the middle line dorsally the vertebral arches 

 are separated by conspicuous apertures, the median sacral fora- 

 mina. 



The caudal or coccygeal vertebrae (vertebrae caudales, 

 s. coccygeae) are sixteen in number. There are segments of small 

 size, increasing slightly to the third, and then gradually decreasing 

 to the end of the column. The arches are complete in the first 



