362 



NERVOUS SYSTEM OF VERTEBRATA. 



united into one continuous mass ; and this mass, constituting 

 the Brain and Spinal Cord, is inclosed within the bony 



Fig. 190. NERVOUS SYSTEM OF OCTOPUS (PouLP). 



casing formed by the skull and vertebral column, in such a 

 manner as to be protected by it from injuries to which it 

 would otherwise be continually liable ( 72, 73). We have 

 seen that among the Invertebrated classes the nervous system 

 has no such peculiar defence, but lies among the other organs, 

 sharing with them the protection afforded by the general hard 

 envelope of the body. But in the Vertebrata, its development 



