CLASSIFICATION AND CKEATION. 69 



Reptile, or be balanced on two legs, while the 

 front limbs become wings, as in Birds, or be 

 raised upon four strong limbs terminating in paws 

 or feet, as in Quadrupeds, or stand upright 

 with head erect, while the limbs consist of a pair 

 of arms and a pair of legs, as in Man, does not 

 in the least affect that structural conception un- 

 der which they are all included. Every Verte- 

 brate has a backbone ; every Vertebrate has a 

 solid arch above that backbone and a solid arch 

 below it, forming two cavities, no matter 

 whether these arches be of hard bone, or of carti- 

 lage, or even of a softer substance ; every Verte- 

 brate has the brain, the spinal marrow or spinal 

 cord, and the organs of the senses in the upper 

 cavity, and the organs of digestion, respiration, 

 circulation, and reproduction, in the lower one; 

 every Vertebrate has four locomotive appendages 

 built of the same bones and bearing the same re- 

 lation to the rest of the organization, whether 

 they be called pectoral and ventral fins, or legs, 

 or wings and legs, or arms and legs. Notwith- 

 standing the rudimentary condition of these limbs 

 in some Vertebrates and their difference of ex- 

 ternal appearance in the different groups, they 

 are all built of the same structural elements. 

 And even where they seem wanting, as in Ser- 

 pents, a minute study of the gradual reduction 

 of the locomotive appendages in various groups 



