254 THE BIOLOGY OF THE AHIMAL 



The cranial nerves are numbered in the order 

 of their origin from the anterior towards the pos- 

 terior part of the brain : 



1. The first, or olfactory nerve, runs from the 

 olfactory lobe to the membrane lining the 

 nasal cavity. 



2. The second, or optic nerve, arises below the 

 optic lobe, and passes through the optic chiasma 

 to the eye on the opposite side. 



3. The third, or motor oculi, originates on the 

 ventral surface of the brain near the pituitary 

 body, and supplies some of the eye muscles. 



4. The fourth, or pathetic, arises on the dorsal 

 surface of the brain in front of the cerebellum, 

 leaves the cranium in front of the optic nerve, 

 and runs to one of the eye muscles. 



6. The fifth, or trigeminal, runs forward from 

 the anterior part of the meduUa to leave the 

 cranium immediately in front of the auditory 

 capsule. Just within the place of exit look for 

 the Gasserian ganglion. "What is its exact 

 position ? Compare it with the spinal and with 

 the sympathetic ganglia. On the outer side 

 of the ganglion the nerve divides into two 

 branches : the first or ophthalmic nerve runs 

 to the skin of the front part of the head and 

 to the nasal cavity; the second or maxillo- 

 mandibularis divides into two branches, the 

 maxillary nerve, which runs to the skin of 

 the upper jaw and to the lower eyelid, and the 

 mandibular nerve, which supplies parts of 

 the lower jaw. 



6. The sixth, or abducens, originates near the 

 median ventral line of the medulla, behind the 



