VERTEBRAL COLUMN 



107 



the seventh lumbar vertebra, by its caudal end with the first caudal 

 vertebra, and by the cephalic part of the lateral surface with the ilium 



of the innominate bone. 



FIG. 78. 



PLAN OF A SACRAL VERTEBRA. END VIEW. 



Ossification. The sacrum appears to be developed from twenty- 

 four centres, whereof nine are the primary centres, three for each 

 vertebra. The fifteen secondary centres are : six in the epiphyseal 

 plates (two for each body), two in the costal elements of the lateral 

 masses of the first vertebra (Fig. 78), four in the auricular surfaces 

 and lateral margins, and three in the tips of the spinous processes. 

 Further studv may show additional centres in the regions of the free 



/ i/ O 



and coalesced articular processes. 



THE CAUDAL VERTEBRA. 



The Eighteen to Twenty-six Caudal Vertebrae form the bony 

 support of the tail, constituting about three-sevenths of the entire 

 vertebral column and its slender and most movable region. The first 

 four or five vertebra? are in the terminal movable part of the dorsal 

 wall of the pelvis ; the remaining vertebrae are in the part of the tail 

 which projects freely behind the body. The typical caudal vertebrae 

 are in the middle of the region ; the first few resemble the sacral 

 vertebra?, and the last five or six are bony cylinders with mere traces 

 of processes. 



A TYPICAL CAUDAL VERTEBRA. 



The Eighth Caudal Vertebra (Figs. 79, 80, 81) is a bony cylinder 

 enlarged at both ends. Its long diameter is twice as great as its trans- 



