THE CRANIAL NERVES. 



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muscles which move the eyeball and also to that which 

 lifts the upper eyelid. The four-sided space bounded by 

 the optic tracts and commissure in front and the third 

 pair of nerves behind, and having on it the pituitary body 



Fio. 70. The base of the brain. The cerebral hemispheres are seen over- 

 lapping all the rest. 7, olfactory lobes ; II, optic tract passing to the optic 

 commissure from which the optic nerves proce~ed ; ///, the third nerve or motor 

 oculi ; IV, the fourth nerve or patheticus ; V, the fifth nerve or trigeminalis; 

 VI, the sixth nerve or abducens ; VII, the seventh or facial nerve or portio 

 dura ,' VIII, the auditory nerve or portio mollis ; IX, the ninth or glosso- 

 pharyngeal ; X, the tenth or pneumogastric or vagus ; XL the spinal acces- 

 sory ; XII, the hypoglossal ; ncl, the first cervical spinal nerve. 



and the corpora albicantia, lies beneath the third ventricle, 

 so that a probe pushed in there would enter that cavity. 



The fourth pair of nerves, IV (pathetici), arise from the 

 front part of the roof of the fourth ventricle. From there, 



