704 THE NERVES. 



who doubled the seventh pair of Willis, and reduced his eighth into three 

 distinct pairs, according to considerations derived from the destination and 

 uses of these nerves. The number of pairs of cranial nerves, their order of 

 succession, and their nomenclature was then established in the following 

 manner : 



1st pair or olfactory nerves . . . corresponding to the 1st pair of Willis. 

 2nd pair or optic nerves .......... 2nd pair 



3rd pair or common motores oculorum nerves . . . 3rd pair 



4th pair or pathetic! nerves ......... 4th pair 



5th pair or trigeminal nerves ......... 5th pair 



6th pair or abducentes nerves ......... 6th pair 



7th pair or facial nerves .......... \ _ , . 



8th pair or auditory nerves ......... j- an pai 



9th pair or glosso-pharyugeal nerves ....... j 



10th pair or pneumogastric nerves ....... 1 8th pair 



llth pair or accessory or spinal nerves ...... j 



12th pair or great hypo-glossal nerves ...... 9th pair 



In the following table, these nerves are classed according to their 

 properties : 



l.Nervesofspe- 



cial sense . aditory neryes ......... gth 



2. Mixed nerves J trigeminal nerves ........ 5th 



with double < glosso-pharyngeal nerves ..... ' . 9tli 



roots . . I pneumogastric nerves ....... 10th 



common motores oculorum nerves . . . 3rd 



pathetici nerves ........ 4th 



abduceutes nerves ........ 6th 



facial nerves ......... 7th 



accessory or spinal nerves ...... llth 



great hypo-glossal nerves ...... l^th 



3. Motor nerves 

 with single 

 roots 



(Sir Charles Bell considered the fourth, seventh, and eighth nerves as 

 forming a separate systom, and to be allied in the functions of expression 

 and respiration. In consonance with this view, he termed them respiratory 

 nerves, and named that portion of the medulla oblongata from which they 

 arise the respiratory tract.) 



One of the characteristics of the cranial nerves being their diversity, it 

 is scarcely possible to study them as a whole, and it is only in their origin 

 that they resemble each other in some points. We therefore confine 

 ourselves to those general considerations which alone touch this part of 

 their description. 



Do the cranial nerves proceed from the three principal apparatus com- 

 posing the encephalon, or are they furnished by two, or even one of these ? 

 This is the question that should first be discussed. If it is evident to 

 everyone that the isthmus gives rise to the majority of the encephalic 

 nerves, and that the cerebellum has nothing whatever to do with their 

 emission, it is not agreed among anatomists as to the part the brain-proper 

 takes in this emission. Two pairs of cranial nerves are indeed considered 

 by several authors as emanating from the latter organ, while others regard 

 them as derived from the isthmus. According to the first, only ten en- 

 cephalic pairs of nerves belong to this prolongation of the spinal cord, the 

 other two the olfactory and optic nerves proceed from the brain; while 

 the second aver that all the cranial nerves without exception arise from the 

 medulla oblongata. Let us endeavour to discover the truth. 



It is certain that this difference of opinion on a point apparently easy of 



