THE CRANIAL NERVES 



921 



are purely efferent, some purely afferent, and others mixed. So 

 that if we are to look upon the motor nerves as the homologues of 



the ventral roots, the dorsal 

 (posterior) root-fibres cor- 

 responding to them must be 

 represented in the other 

 cranial nerves. Thus, the 

 sensory portion of the mixed 

 fifth nerve, and the purely 

 afferent auditory nerve, must 

 be supposed to contain 

 fibres corresponding to seve- 

 ral dorsal roots. 



Fig. 367. Nuclei of Cranial Nerves (Toldt). 

 Motor red, sensory blue. The numbers 

 correspond to the cranial nerves. 



The first or olfac- 

 tory nerve consists 

 of fine fibres, each 

 of which is a process 

 of an olfactory cell 

 (Fig. 369). The ol- 

 factory cells, which 

 are really peripheral 

 nerve-cells, lie among 

 the epithelial cells in 

 the olfactory region 

 of the Schneiderian 

 membrane, the com- 

 mon lining of the 

 nostrils. Each olfac- 

 tory cell gives off two 

 pr9cesses, a short 

 one, representing a dendrite, which runs out to the surface of the mucous 

 membrane, and a longer but more slender process, representing an axon, 



Fig. 368. Nuclei and Roots of Cranial 

 Nerves (Toldt). Lateral view. Motor 

 red, sensory blue. 



