806 THE NERVES. 



Ist pair, or olfactory nerves . corresponding to tlie lat pair of Willia. 



2nd pair, or optic nerves 2nd pair „ 



3rd pair, or common raotores oculorum nerves 3rd pair ^ 



4th pair, or pathetici nerves 4th pair „ 



5th pair, or trigeminal nerves 5th pair , 



6tli pair, or abduoeutes nerves 6th pair „ 



7th pair, or facial nerves \ _ , 



8tli pair, or auditory nerves / P ** 



9tii pair, or glosso-pharyngeal nerves ....... \ 



10th pair, or pneumogastric nerves r 8th pair „ 



11th pair, or accessory or spinal nerves ) 



12th pair, or great hypoglossal nerves 9th pair „ 



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



, ^^ , . , [ olfactory nerves or Ist pair. 



1. Nerves of special tj,^i^^^^^^^ 2nd,, 



sense • • • ( auditory nerves 8th „ 



2. Mixed nerves { trigeminal nerves 5th „ 



with double -! glosso-pharyngeal nerves 9th „ 



roots . . . ( pneumogastric nerves 10th „ 



common motores oculorum nerves .... 3rd „ 



pathetici nerves 4th „ 



8. Motor nerves i , , . /.. i 



.,, • 1 ' abducentes nerves btn 



with single \ r . , ,,., 



. I ^^^^^^ nervi-s 7tn „ 



' f accessory or spinal nerves 11th „ 



^ great hypo-glossal nerves 12th „ 



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

 ing a separate system, and to be allied in the functions of expression and respira- 

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

 named that portion of the medulla oblongata from which they arise, the 

 respirator// 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 07igi7i that 

 they resemble each other in some points. A good idea of their origin is given 

 in Fig. 452. 



Preparation of the cranial nerves. — Four preparations are necessary for the study of the 

 cranial nerves : 



1. A brain extracted after opening the cranium by its base, and har.lened by prolonged 

 immersion in alcohol or very diluted nitric acid. This piece permits the origin of the nerves 

 to be studied (Fig. 424). 



2. The superficial nerves of the head ; these are the auricular nerves, and the divisions of 

 the subzygomatic plexus, with the infra-orbital and mental brandies, as well as the superficial 

 ramusoules of the three nerves of the ophthalmic branch of the fifth pair (Fig. 168). 



3 A piece disposed as in Fig. 454, for the study of the maxillary nerves. To prepare it, 

 the greater part of the masseter muscle should be removed in dissecting the masseteric nerve ; 

 the globe of the eye must be extirpated, the orbital and zygomatic processes excisi d, the two 

 maxillary sinuses opened, and the branch of the inferior maxillary bone chiselled off as in the 

 figure. Lastly, the anastomosis of the facial with the subzygomatic nerve is dissected, by 

 cutting away the parotid gland. 



4. The deep nerves, including those of the globe of the eye ; this preparation should be 

 made by following exactly the in.-tructions given for dissecting the arteiies of the head. Figs. 

 450 and 454 will serve as guides for details. 



The pneumogastric and spinal nerves, which are not included in these considerations, 

 ehould be prepared and studied at the same time as the great sympathetic. When treating of 

 the latter, we will refer to them. 



Preparations 2. 3, and 4 may be made on one head, and simultaneously. With this object, 

 the head is skinned, and the facial panniculus, beneath which the branches of the subzygo- 

 matic plexus lie, is removed. The parotid gland is carefully dissected off, to expose the sub. 



