Cranial Nerves. 



THE Cranial Nerves, nine in number on each side, include those nerves which 

 arise from some part of the cerebro-spinal centre, and are transmitted through 

 foramina in the base of the cranium. They have been named numerically, 

 according to the order in which they pass out of this cavity. Their names are 

 also derived from the part to which each is distributed, or from the special 

 function appropriated to each. Taken in their order, from before backwards, 

 they are as follows : 



1st. Olfactory. ,_ , j Facial or Portio dura. 



2d. Optic. ' ( Auditory or Portio mollis. 



3d. Motor oculi. I Glosso-pharyngeal. 



4th. Pathetic. 8th. < Pneumogastric or Par vagum. 



5th. TrifaCial or Trigemini. ( Spinal accessory. 



6th. Abducens. 9th. Hypoglossal. 



If, however, the 7th pair be considered as two, and the 8th pair as three distinct 

 nerves, then their number will be increased to twelve, which is the arrangement 

 adopted by Sommering. 



The cranial nerves may be subdivided into four groups, according to the 

 peculiar function possessed by each, viz., nerves of special sense; nerves of 

 common sensation ; nerves of motion ; and mixed nerves. These groups may 

 be thus arranged : 



1. Nerves of /Special Sense. 2. Nerves of Motion. 



Olfactory. Jfoto r oculi. 



Optic Pathetic. 



Auditorv Part of third division of fifth (de- 



Part of glosso-pharyngeal (described scr ^ under the fifth nerve > 



under the eighth pair, p. 555). f' 54 )' ' 



Lingual branch of the fifth (described Abducens. 



under the fifth nerve, p. 550). 



Hypoglossal. 



4. Mixed Nerves. 



3. Nerves of Common Sensation. Pneumogastric _ (described under 



the eighth pair, p. 55 /). 



tth (greater portion). Spinal access0 ry (described under 



Part ot glosso-pharyngeal. the eighth pair, p. 560). 



All the cranial nerves are connected to some part of the surface of the brain. 

 This is termed their superficial or apparent origin. But their fibres may, in all 

 cases, be traced deeply into the substance of the organ. This would form their 

 deep or real origin. 



1. NERVES -QS SPECIAL SENSE. 

 OLFACTORY NERVE. 



The FIRST or OLFACTORY NERVE, the special nerve of the sense of smell, may 

 be regarded as a portion of the cerebral substance, pushed forwards in direct 

 relation with the organ to which it is distributed. It arises by three roots. 



The external or long root is a narrow white medullary band, which passes 

 outwards across the fissure of Sylvius, into the substance of the middle lobe of the 

 cerebrum. Its deep origin may be traced to the corpus striatum 1 , the superficial 

 fibres of the optic thalamus 2 , the anterior commissure 3 , and the convolutions of 

 the island of Eeil. 



1 Vicussens, Winslow, Monro, Mayo. a Valentin. Cruveilhier. 



535 



