THE NERVOUS SYSTEM 165 



sphere. The olfactory bulb is the enlargement which projects 

 from the frontal pole of the hemisphere. 



The cerebellum, or small brain, is lodged in the posterior fossa 

 of the cranium. It resembles a globe in shape and differs from 

 the cerebrum in having a finer marked exterior. It is divided 

 into the median vermis and two lateral hemispheres. For the 

 most part it is composed of gray substance, but a core of white 

 material resembling the branchings of a tree may be seen when 

 the cerebellum is sectioned. 



The pons (Varolii) is a bridge-like affair, which lies between the 

 medulla and the cerebral peduncles. It connects the former with 

 the cerebrum, and also the right and left portions of the 

 cerebellum. 



The medulla oblongata, or bulb, is the connecting link be- 

 tween the pons and the spinal cord. It differs from the brain 

 proper in having the white substance externally. 



The cranial nerves arise directly from the brain. They are 

 of very unequal size and emerge through openings in the skull. 

 There are twelve pairs, which have been numbered and named 

 to identify them. The names indicate the functions or the parts 

 to which they pass. 



The first or olfactory nerve supplies the mucous membrane of 

 certain portions of the nasal cavity and has to do with the special 

 sense of smell. 



The second or optic nerve furnishes the eyes and has to do with 

 the special sense of sight. 



The third or oculomotor nerve supplies all except two of the 

 muscles of the eyeball. 



The fourth or trochlear nerve is the smallest of the cranial nerves. 

 It ends in the posterior parts of the superior oblique muscle of 

 the eyeball. 



The fifth or trifacial nerve is the largest of the series. It has 

 both motor and sensory fibers for different parts of the face and 

 mouth and has a very important function to perform. 



The sixth or abducent nerve supplies the retractor muscles of the 

 eyeball. 



The seventh or facial nerve is responsible for the movements of 

 most of the muscles of the face. It consists of both motor and 

 sensory parts. 



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