The Nervous System 



217 



331, The Cranial Nerves. The cranial or cerebral nerves 

 consist of twelve pairs of nerves which pass from the brain 

 through different openings in the base 

 of the skull. They are distributed 

 over the head and face, and also to 

 some parts of the trunk and to cer- 

 tain internal organs. These nerves 

 proceed in pairs from the correspond- 

 ing parts on each side of the brain. 



332. Distribution and Functions 

 of the Cranial Nerves. The cranial 

 nerves are thus arranged in pairs : 



The first pair are the olfactory nerves, 

 the special nerves of smell. 



The second pair are the optic nerves, 

 which pass to each eyeball, and are 

 devoted to sight. 



The third, fourth, and sixth pairs 

 control the muscles of the eyes. 



Each of the fifth pair of nerves is FIG. 119. Anterior View of 

 in three branches and proceeds mainly the Medulla Oblongata. 

 to the face. They are called tri-facial A, chiasm of the optic nerves ; 

 nerves, and are partly sensory and ^, optic tracts ; C, motor oculi 

 partly motor. communis ; A fifth nerve ; *> 



The seventh pair, the facial nerves, 

 control the facial muscles. The eighth 

 pair are the auditory, or nerves of hear- 

 ing, and are distributed to- the special 

 organs of hearing. 



The ninth pair, the glossopharyngeal 

 nerves, are partly sensory and partly 

 motor. Each nerve contains two roots : 

 one a nerve of taste, which spreads 

 over the back part of the tongue; the other a motor nerve, 

 which controls the muscles engaged in swallowing (Fig. 123). 



The tenth pair, the pneumogastric nerves, also known as the 

 vagi, or wandering nerves, are the longest and most important 

 of all the cranial nerves. They are both motor and sensory. 



motor oculi externus; F, facial 

 nerve; If, auditory nerve; 

 /, glossopharyngeal nerve ; 

 K, pneumogastric ; Z,, spinal 

 accessory; M, cervical nerves; 

 N, upper extremity of spinal 

 cord; O, decussation of the 

 anterior pyramids ; P, hypo- 

 glossal nerve ; JR, anterior 

 pyramids ; S, pons Varolii. 



