CHAPTER XXI. 

 THE CRANIAL NERVES. 



The nerve-trunks which serve as channels of communication 

 between the encephalon and the structures of the head, the face, 

 and in part the organs of the thorax and abdomen, pass through 

 foramina in the walls of the cranium, and for this reason are termed 

 cranial nerves. 



According to the classification now generally adopted, there are 

 twelve cranial nerves on either side of the median line, which, enu- 

 merated from before backward, are as follows (Fig. 235): 



First or Olfactory. Seventh or Facial. 



Second or Optic. Eighth or Auditory. 



Third or Oculo-motor. Ninth or Glosso-pharyngeal. 



Fourth or Patheticus. Tenth or Pneumogastric or Vagus. 



Fifth or Trigeminal. Eleventh or Spinal Accessory. 



Sixth or Abducens. Twelfth or Hypoglossal. 



The cranial nerves may be classified physiologically in accordance 

 with their functional manifestations into three groups, viz. : 



1 iV ^\ 



1. Nerves of Special Sense: e.g., Olfactory, Optic, Auditory, Gustatory (Glosso- 



pharyngeal). 



2. Nerves of General Sensibility: e.g., Large root of the Trigeminal, Glosso-- 



pharyngeal, and Pneumogastric. 3 S 



3. Nerves of Motion: e. g., Oculomotor, Pathe^fcus, the small root of the TrigeminaJ, 



Facial, Spinal Accessory, and Hypoglossal. 



Though this classification in the main holds true, it must be borne 

 in mind that modern investigations have demonstrated that the glosso- 

 pharyngeal and pneumogastric nerves contain even at their junction 

 with the medulla oblongata a number of efferent or motor fibers, 

 and to this extent are mixed nerves. 



The Origins of the Cranial Nerves. In accordance with 

 modern views as to the origins of nerves in general, it may be stated 

 that 



The nerves of special sense have their origin respectively in the 

 neuro- epithelial cells in the mucous membrane of the olfactory region 

 of the nose, in the ganglion cells of the, ffitl na - m tne ce ^ s f & e sfitffrl 

 ganglion of the cochlea anfl tflf gfrnplinn nf Scarpa, and in the cells 



nf rhf> -ppfrnpg anH ^gnjsirjTangHii li'i^Jjj |1| . *]]c o f these ganglia 



dendrites pass peripherally to become associated with specialized 

 end-organs, while axons pass centrally in well-defined bundles to 



