ANATOMY OF THE NEUVOUS SYSTEM. 173 



and commissure in front and the third pair of nerves behind, 

 and having on it the pituitary body and the corpora albi- 

 cantia, lies beneath the third ventricle, so that a probe pushed 

 in there would enter that cavity (see Fig. 75). 



in 



FIG. 77. The base of the brain. The cerebral hemispheres are seen overlap- 

 ping all the rest. 7, olfactory lobes; II, optic tract passing tothe optic commissure 

 from which the optic nerves proceed ; HI, the third nerve or motor oculi ; 1 V, the 

 fourth nerve or patheticus ; V, the fifth nei*ve or trigeminalis; VI. thn 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 pneu- 

 mogastric or vagus; XI, the spinal accessory; XII, the hypoglossal; ncl, the first 

 cervical spinal nerve. 



The fourth pair of nerves, IV (patlietici\ arise from the 

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

 each curls around a crus cerebri (the cylindrical mass seen 

 beneath it in the figure, running from the pons Varolii to 

 enter the under surface of" the cerebral hemispheres) and ap- 

 pears on the base of the brain. Each goes to one muscle of 

 the eyeball. 



The fifth pair of nerves (trigeminales), V, resemble the 





