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HUMAN PHYSIOLOGY 



The Cranial Nerves. Of the cranial nerves, only 

 one pair join the cerebrum. These are the olfactory 

 nerves, diffuse collections of fibers which lead into the 

 brain from microscopic receptors in the upper part of 

 the nasal passages. As the name implies, these nerves 



FIG. 30. The under surface of the human brain. The manner of 

 origin of the cranial nerves is shown more fully upon the left side of the 

 figure (which is the right half of the brain). Roman numerals are ap- 

 pended to those nerves to which particular reference is made in the text. 



are responsible for the sense of smell. The olfactory 

 nerves are the farthest forward of all in the cranial 

 series, so they are spoken of as the first cranial nerves. 

 The second pair are the optic nerves, trunks of large size 

 coming from the eyeballs to a place on the under sur- 

 face of the brain where they appear to cross in the form 

 of a letter X. Their fibers enter the brain-stem close 



