822 



PHYSIOLOGY. 



the cord its sensory impressions, and motor nerves to conduct to the 

 muscles the motor reactions. In the same way the central conduc- 

 tors of the brain bring to it sensory impressions and by its motor 

 fibers carry out motion. Hence it results that all of the sensory 

 fibers of centripetal course have their origin, not in the gray nuclei 

 of the medulla oblongata, but in the ganglia annexed to the dorsal 

 roots of the cranial nerves. 



The oblongata nuclei are but terminal nuclei, for in them the 

 sensory fibers terminate by fine arborizations which surround the 

 central cells without penetrating them. The termination is identical 

 with that of the sensory roots of the spinal nerve. 



^ W W .! rrF--p4-:j:::-^ ;/ 1' 



Fig. 372. Position of the Nuclei of the Cranial Nerves. 

 (After EDINGER.) 



The medulla oblongata and pons are imagined as transparent. The nuclei 

 of origin (motor), black; the end nuclei (sensory), red. 



The sensory fibers of the tenth, ninth, seventh, and fifth pairs 

 of cranial nerves, as well as that of the auditory, originate in their 

 respective ganglia. Thus, there is the jugular for the tenth pair, 

 the jugular and petrosal for the ninth pair, the geniculate for the 

 seventh, Gasserian for the fifth, and Scarpa's and spiral ganglia for 

 the eighth pair. 



On the contrary, the motor fibers of the cranial nerves arise in 

 the central cells of the medulla and pons, just like the motor fibers 

 of the spinal cord. Thus, fine anatomy demonstrates that the 

 cranial, like the spinal, nerves have double roots. 



Decussations. The afferent or sensory cranial nerves do not 

 decussate. Of the motor cranial nerves, the third and fourth, the 



