RECORD OF LIFE IN THE ROCKS. 177 



Fig. 96. 



common language, made up of vertebra.* Through this 

 chain of bones runs a nervous extension of the brain 

 called the spinal marrow, from which nerves 

 branch out to different parts of the body. In 

 Fig. 97 you see represented a single vertebra 

 from the spinal column or back-bone of man, 

 a being its front part, and b its pointed rear 

 Fig. 97. part, which you feel on tracing the line of the 



* Sometimes animals are spoken of as being in two great classes, 

 the Vertebrates and the Invertebrates, those which have and those 

 which have not vertebrae, the prefix in being a particle of negation. 

 The Invertebrates include the three great classes already spoken of 

 Radiates, Mollusks, and Articulates. 



H2 



