THE BRAIN 345 



G. The Eoots of the Cerebral Nerves. 



There are twelve pairs of cerebral or cranial nerves in the 

 rabbit, aU of which, with the exception of the fourth pair, 

 arise from the ventral surface or from the sides of the brain. 



Identify, and clean the nerve-roots on one side of the brain, 

 in the order given below, taking great care not to drag them 

 away from the brain. 



1. The olfactory nerve arises, by many roots, from the 



ventral surface of the anterior end of the olfactory 

 lobe. These roots are almost necessarily removed 

 in taking out the brain. 



2. The optic nerve is a stout nerve, running forwards 



from the anterior border of the optic chiasma, and 

 then curving outwards. 



3. The oculo-motor nerve is smaU, and arises from the inner 



border of the crus cerebri, close to the middle line, 

 and immediately behind the corpus mammiUare. 



4. The pathetic nerve is very small. It arises from the 



dorsal surface of the valve of Vieussens, close to the 

 middle Hne, and just behind the optic lobes. It then 

 runs round the side of the brain to the ventral 

 surface, lying between the cerebeUum and optic lobe. 



Find the nerve on the ventral surface, and follow it round 

 the side of the brain to its origin. 



5. The trigemuial nerve is very large, and arises by two 



closely apposed roots from the sides of the hinder 

 border of the pons Varolii. Of the two roots the 

 inner and smaller one is motor, the larger outer 

 one sensory in function. 



6. The abducent nerve is very slender, and arises from 



the ventral surface of the medulla, close to the 

 middle hne, and immediately behind the pons 

 Varolii. 



7. The facial nerve arises from the outer side of the 



anterior end of the corpus trapezoideum, imme- 

 diately behind the trigeminal nerve. 



