VERTEBRATE ANIMALS 



OF THE 



NoETHEEN United States. 



VER TEBRA TA. 



(The Vertebrates.) 



The Vertebrates are, in popular language, " animals 

 with a back-bone." They are distinguished from all 

 other animals, says Prof. Huxley, " by the circumstance 

 that a transverse and vertical section of the body 

 exhibits two cavities, completely separated from one 

 another by a partition. The dorsal cavity contains the 

 cerebro-spinal nervous system; the ventral, the alimen- 

 tary canal, the heart, and, usually, a double chain of 

 ganglia, which passes under the name of the ' sympa- 

 thetic' A vertebrated animal may be devoid of 

 articulated limbs, and it never possesses more than two 

 pairs. These are always provided with an internal 

 skeleton, to which the muscles moving the limbs are 

 attached." 



Without further discussion of this great group of 

 animals, we will proceed at once to the consideration of 

 the classes. Of existing vertebrates, we here recognize 



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