NERVOUS SYSTEM. Ill 



Structure of the Brain. 



Gray structure externally and dipping down into the convolu- 

 tions. There are seven layers in the cortical substance (Kolliker). 



The white substance is found internally and runs, as fibres, in 

 various directions. 



THE CRANIAL NERVES. 



There are twelve in number (Sommering). 

 ist, or Olfactory. Nerve of smell (see Smell). 



Superficial Origin. See Olfactory lobe. 



Deep Origin. Corpus striatum and transverse fibres of pons. 



Exit. Through cribriform plate of ethmoid. 



Distribution. To nasal septum and ethmoidal cells in upper 

 third of nasal fossae. 



Function. Well marked and presides over sense of smell. 

 2d, or Optic. 



Origin. From commissure and optic tracts which arise from 

 thalamus and corpora quadrigemina. 



Exit. Optic foramen. 



Distribution. To retina (see Eye). 



Function. Nerve of sight. 

 3d, or Oculo-motor. 



Superficial Origin. From crura near to interpeduncular fissure. 



Deep Origin. Anterior border of pons. 



Exit. Smallest supra-sphenoidal foramen of orbit. 



Distribution. To all muscles of eye except external rectus, 

 great oblique and part of the posterior rectus, and by ophthalmic 

 ganglion to the iris. 

 4th, or Patheticus. 



Superficial Origin. Band of Reil behind corpora quadrigemina. 



Deep Origin. From interior isthmus. 



Exit. By smallest supra-sphenoidal foramen to orbit. 



Distribution. To great oblique muscle. 

 5th, or Trifacial. 



Superficial Origin. By two roots, the larger, or sensory, from 

 the sides of the pons, the motor from pons, near the other. 



Deep Origin. Sensory root from restiform body of medulla, 

 the interior cells of the isthmus and nuclei of other nerves. Motor 

 root from antero-lateral fasciculus of medulla. 



