100 



MAMMALIAN ANATOMY 



FIG. 71. 



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TRANSVERSE SECTION OF SACRUM THROUGH SACRAL 

 FORAMINA (DIAGRAMMATIC). 



verse processes of the third vertebra. The caudal end of the transverse 

 processes of the third vertebra project laterally and toward the tail, 

 and are known as the inferior angles. This union of the transverse 

 processes does not comprise their entire transverse width, but is confined 

 to the lateral portion. There are thus produced two pairs of vertical 



canals, which open on the 

 dorsal and ventral surfaces 

 by the dorsal and ventral 

 sacral foramina (Fig. 71). 

 Each of these canals 

 has its lateral-cephalic, its 

 lateral, and its caudal walls 

 formed of the contiguous 

 transverse processes ; but 

 its medial-cephalic wall, 

 which is dorsally formed 

 of the laminae and ven- 

 trally of the bodies, is 

 largely occupied by a fora- 

 men leading into the neural canal. This foramen is at once recog- 

 nized as the intervertebral foramen of the other vertebrae. Each 

 intervertebral foramen gives exit to a sacral spinal nerve whereof the 

 dorsal and ventral branches leave the sacrum by the dorsal and 

 ventral foramina respectively. 



Inasmuch as in macerating the bones of a young skeleton the 

 sacral vertebras may be broken apart, it is important to note the 

 characters whereby these vertebra? may be distinguished from all other 

 vertebra? and from one another. They differ from all the cervicals, 

 except the seventh, by the absence of the cephalo-caudal arterial canal ; 

 from the seventh, by their short spinous processes. They differ from 

 the thoracics by the absence of facets for the attachment of the ribs, 

 and from the lumbars by their dorso-ventrally compressed shape, by 

 their comparatively small transverse processes, and by the absence 

 of mammillary and accessory processes. They may be distinguished 

 from the first vertebrae of the caudal region, since these have no 

 spinous processes and have narrow, free transverse processes which 

 point toward the tip of the tail. The last caudal vertebra? have 

 entirely different and cylindrical forms. 



