CRANIAL NERVES. 269 



forwards, ventral to the rectus inferior, which it 

 supplies, to the obliquus inferior, in which it ends. 

 As it crosses the rectus inferior it is joined by a 

 branch from the fifth nerve. 



Gently press aivay the optic lobe from the skull-wall, so as 

 to see the third nerve within the skull, and also the point at 

 tohich it enters the orbit. In the orbit the branches to the 

 rectus internus and rectus superior are easily dissected from 

 above. To trace the branch to the obliquus inferior place the 

 fish on its side, and turn the eyeball upwards so as to expose 

 the nerve from below. 



4. The fourth or pathetic nerve is a very slender nerve 



which arises from the dorsal surface of the brain, in 

 the angle between the optic lobe and the cerebellum, 

 and almost in the median plane. From the brain 

 it runs forwards and outwards to the skull-wall, 

 which it perforates a little in front of the middle of 

 the orbit, dorsal to the optic nerve, and immediately 

 ventral to the ophthalmic branches of the fifth and 

 seventh nerves. In the orbit it runs outwards and 

 forwards to the posterior border of the obliquus 

 superior, in which it ends. 



Though very slender, the fourth nerve is easy to trace. 

 Lift up the front end of the cerebellum to see its origin 

 between the cerebellum and the optic lobes ; trace it forwards 

 luithin the skull, and in the orbit outwards to the obliquus 

 superior. 



5. The fifth, seventh, and eighth nerves arise very close 



together from the side of the medulla at its widest 

 part, opposite the posterior part of the cerebellum. 

 The eighth or auditory nerve, which is the hindmost 

 of the three, enters the auditory capsule at once ; 

 while the fifth and seventh nerves pass outwards 

 through the skull-wall, by a foramen at the posterior 

 and inner angle of the orbit, immediately behind the 

 origins of the recti muscles. 



