178 



DISSECTION OF THE BRAIN. 



The cranial nerves may be regarded either as nine or twelve pairs, 

 according to the mode of classifying them. 1 



The several nerves may be designated first, second, third, and so forth : 

 this numerical mode of naming applies to all, and is the one generally used. 



But a second name has been derived for some of the nerves from the 

 parts to which they are supplied ; as instances of this nomenclature the 

 terms hypoglossal, pneumogastric, may be taken. And a different ap- 

 pellation is given to others, in consequence of the function conferred on 

 the part to which they are distributed, as the terms auditory and olfactory 

 express. In this way two names may be employed in referring to a nerve: 

 one being numerical, the other local or functional, as is exemplified below. 



The FIRST OR OLFACTORY NERVE (olfactory process) (fig. 53, *) is soft 



Fig. 53. 



Olfactory. 



Optic. 



Motor oculi. 



Trochlear. 



Trigeminal with small and large root. 



Abductor oculi. 



Facial and auditory, the former smalli r 

 and internal. 



Eighth nerve consisting of three 

 trunks in a line : the upper, glosso- 

 pharyngeal ; the middle, pneurao- 

 gastvic ; and the lowest spinal ac- 

 cessory. 



Boots of attachment of the hypoglossal 

 nerve. 



ORI-JIN OP THE CRANIAL NERVES. 



and pulpy, being destitute f a neurilemma ; and it may be considered an 

 advanced part of the brain, for it hasTiotlTgray substance and white fibres 

 in its composition, like the cerebrum. 



The olfactory process is a flat-looking band, wider at each end than in 

 the middle, which is lodged in a sulcus on the under aspect of the frontal 

 lobe of the cerebrum, and is kept in position by the reflection of the arach- 

 noid membrane over it. When the so-called nerve is raised from the 



1 Those anatomists, who take the smaller number after the example of Willis, 

 include in one nerve all the trunks contained in the same aperture of the skull : 

 as in the case of the eighth nerve, which consists of three trunks in the foramen 

 jugulare. But those who are disposed with Sommerring to enumerate twelve 

 nerves, consider each of the three trunks of the eighth nerve before mentioned, 

 to constitute a separate cranial nerve, notwithstanding that it may be combined 

 with others in the foramen of exit. 



