152 ELEMENTS OF COMPARATIVE ZOOLOGY. 



GNATHOSTOMATA. 



In the Gnathostomata jaws are always developed; the 

 skeleton, whether of cartilage or bone, is a true support to 

 the body ; usually paired limbs occur, and the nostrils are 

 always paired. The general account of the Vertebrata in 

 the preceding pages applies especially to the Gnathostomes. 

 This group is divided into three subbranches : 



SUBBRA^CH I. ICHTHYOPSIDA (p. 55). 



SUBBRANCH II. SAUROPSIDA (p. 85). 

 SUBBRANCH III. MAMMALIA (p. 97). 



