CHAPTER I 

 OSTEOLOGY AND ARTHROLOGY 



THE TRUNK 



The Vertebral Column 



We commence the study of the skeleton with a description 

 of the trunk. 



The trunk being, in quadrupeds, horizontal in direction 

 (Fig. i), the two regions of which it consists occupy, for this 

 reason, the following positions : the thorax occupies the 

 anterior part, the abdomen is placed behind it ; the vertebral 

 column is horizontal, and is situated at the superior aspect 

 of the trunk ; it projects beyond the latter : anteriorly, to 

 articulate with the skull ; and, posteriorly, to form the 

 skeleton of the tail, or caudal appendix. 



The number of the \ertebrae is not the same in all mam- 

 malia. Of the several regions of the vertebral column, the 

 cervical shows the greatest uniformity in the number of the 

 vertebrae of which it consists, with but two exceptions 

 (eight or nine in the three-toed sloth, and six in the manatee) ; 

 we always find seven cervical vertebrae, whatever the length 

 of the neck of the animal. There are no more than seven 

 vertebrae in the long neck of the giraffe, but they are very 

 long ones ; and not less than seven in the very short neck 

 of the dolphin, in which they are reduced to mere plates of 

 bone not thicker than sheets of cardboard. If the cervical 

 region presents uniformity in the number of its bones, it is 

 not so with the other regions of the column. 



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