54 INTRODUCTION. 



These, however, can be proved to be differences in 

 degree, and not in kind. The main support of the 

 trunk, of both the quadruped and fish, is what is 

 termed the vertebral column, composed of a series 

 of small irregularly shaped bones, or vertebrae, in 

 the continuous canal of which is situated a prin- 

 cipal part of the nervous system ; and whether this 

 column be placed throughout on the same horizon- 

 tal plane, as in fishes and most reptiles, or tend 

 about the anterior portion of it, more or less to the 

 perpendicular, as in birds and quadrupeds; and 

 whether the ribs be under the head, so as to lie 

 almost in the mouth, as in fishes, or behind the 

 head, so as to constitute a proper chest, as in the 

 higher tribes of animals, the difference is merely 

 formal. At the anterior extremity of the spinal 

 column is placed the head, composed, in both qua- 

 druped and the lish, of the same essential bones ; 

 and although the cavity is relatively much larger in 

 the former than in the latter, this cannot be re- 

 garded as a fundamental distinction. Nor can those 

 fins of the fish, by which principally it supports 

 itself and moves in the water, be regarded as any 

 thing else than the rudiments, as it were, of the 

 limbs of the quadruped. Similar bones enter into 

 their composition, and they are attached in a similar 

 manner to the trunk; and it is in the highest de- 

 gree interesting to notice, in how very slow and 

 progressive a manner these small and simple fins of 

 the fish rise through the insignificant legs of some 

 reptiles, to the more perfect and available wings or 



