CHAPTER III. 



THE VERTEBRAL COLUMN. 



General Characters. — The Vertebral Column consists of a 

 series of distinct bones called Vertebrcz, arranged in close 

 connection with each other along the dorsal side of the neck 

 and trunk, and in the median line. It is generally prolonged 

 posteriorly beyond the trunk to form the axial support of the 

 appendage called the tail. Anteriorly it is articulated with 

 the occipital region of the skull. 1 



The number of distinct bones of which the vertebral 

 column is composed varies greatly among the Mammalia, 

 the main variation being due to the elongation or otherwise 

 of the tail. Apart from this, in most Mammals, the number 

 is not far from thirty, though it may fall as low as twenty-six 

 (as in some Bats) or rise as high as forty (Hyrax and 

 Choloepus)! 1 



The different vertebras, with some excep'ions, remain 

 through life quite distinct from each other, though closely 

 connected by means of fibrous structures which allow of a 

 certain, but limited, amount of motion between them. 



1 For the sake of uniformity, in all the following descriptions of the 

 vertebral column, the long axis of the body is supposed to be in the 

 horizontal position. 



' 2 These numbers are not exact, owing to the uncertainty in the mode 

 of reckoning the sacral vertebra;. 



