164 



PHILOSOPHY OF ZOOLOGY. 



feathered covering of birds. The thorax is separated from 

 the abdomen by a muscular diaphragm. The pancreatic 

 and bihary ducts enter the intestine by a common opening. 

 The omentum is always present. There are two occipital 

 condyles *. The lower jaw only moves. 



■ The spine of quadrupeds, though exhibiting many common properties, 

 is subject to considerable variations in the number of the vertebrae of which 

 it consists. In the three-toed sloth, the cervical vertebra; amount to nine ; 

 while, in the other quadrupeds, their number is limited to seven. In the 

 ternate bat there are no caudal vertebrae. The following Table, extracted 

 from Cuvier's Comp. Anat., exhibits the number of vertebrae in different 

 species of British quadrupeds. 



