Cranial Nerves. 



, THE Cranial Nerves, nine in number on each side, 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 the cranial cavity. Other names are also given to them 

 derived from the parts to which they are distributed, or from their functions. 

 Taken in their order, from before backwards, they are as follows : 



1st: Olfactory. .-, j Facial (Portio Dura). 



2d. Optic. ' | Auditory (Portio Mollis). 



3d. Motor Oculi. ( Glosso-pharyngeal. 



4th. Pathetic. 8th. < Pneumogastric (Par Yagum). 

 5th. Trifacial (Trigeminus). ( 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 : 



Nerves of /Special /Sense. Nerves of Motion. 



Olfactory. Motor Oculi. 



Optic. Pathetic. 



Auditory. Part of Third Division of Fifth. 



Part of Glosso-pharyngeal. Abduceus. 



Lingual or Gustatory Branch of Fifth. Facial. 



Hypoglossal. 



Nerves of Common /Sensation. Mixed Nerves. 



Fifth (greater portion). Pneumogastric. 



Part of Glosso-pharyngeal. Spinal Accessory. 



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 part is called their 

 deep, or real origin. 



/ & OLFACTORY NERVE. (Fig. 329.) 



The First, or Olfactory Nerve, the special nerve of the sense of smell, may 

 be regarded as a lobe, or portion of the cerebral substance, pushed forward 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 has been traced to the corpus striaturn, 1 the 

 superficial fibres of the optic thalamus, 2 the anterior commissure, 3 and the con- 

 volutions of the island of Reil. 



1 Vieussens, Winslow, Monro, Mayo. J Valentin. 8 Cruveilhier. 



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