1 1 4 The Nervous System 



sory nerves. The eleventh pair, nervus accessorius, and twelfth 

 pair, nervus hypoglossus, are wanting in fishes. 



The spinal nerves are subject to some special modifications, 

 but in the main correspond to similar structures in higher ver- 

 tebrates. The anterior root of each nerve is without ganglionic 

 enlargement and contains only motor elements. The posterior 

 or dorsal root is sensory only and widens into a ganglionic swell- 

 ing near the base. 



A sympathetic system corresponding to that in the higher 

 vertebrates is found in all the Teleostei, or bony fishes, and in 

 the body of sharks and rays in which it is not extended to the 

 head. 



