NERVES OF THE ENCEPHALON. 373 



stated, is open below, when that portion of pia mater is removed, 

 which passes from the cerebellum to the medulla oblongata. 



From what has now been said of the connexion of the pia 

 mater with the ventricles, it will be understood that as their^ur- 

 faces are covered by pia mater, and the removal of it exposes 

 their cavities, they are, in fact, continuations of the external 

 surface of the brain.* 



SECT. VI. OF THE NERVES OF THE ENCEPHALON. f 



These nerves are designated numerically, from before back- 

 wards, and, also, by some peculiarity of distribution or function. 

 This numerical arrangement is the most sanctioned by age and 

 general admission, it is not, however, so unexceptionable as to 

 avoid all objections to it; improvements have therefore been SUQ*- 

 gested from various quarters, founded on particular anatomical or 

 physiological convictions; but the improvements themselves are 

 exposed to objections as strong as the ancient nomenclature. For 

 example, the innovators are not agreed in regard to the proper 

 number of nerves, nor on those which should be considered dis- 

 tinct from each other. Some do not consider the olfactory as a 

 nerve, but only a ganglion; some consider the glosso pharyngeal 

 and parvagum as but one nerve, while others speak.of them as 

 two. Some make but one nerve of the third and sixth, owing to 

 their common distribution to the muscles of the eye. It is evi- 

 dently expedient under these circumstances, to escape a farrago 

 of opinions, by adhering to the most received classification, at 

 least, till the ground of change be better explored and more 

 universally acknowledged. If there be any thing of incalculable 

 importance to the comfort of students and scientific men gene- 

 rally, it is uniformity of language, or rather conformity to a re- 



* In Williams the murderer, examined immediately after his execution, Au- 

 gust 9, 1839, the encephalo spinal fluid, amounting- to from two to three drachms, 

 came out clear and abundant from the fourth ventricle; on cutting through the tu- 

 ica arachnoidea which bounds it below. 



t The more improved observations of modern anatomists having pointed out 

 the fallacy of considering the brain as the source of the spinal marrow, instead of 

 the reverse; it follows, that the proper order of describing the nerves of the en- 

 cephalon, is successively from the spinal marrow. I had adopted this plan, for- 

 merly, but certain considerations of facility in study, have induced me to abandon 

 it after some years of experience. 

 VOL. II. 33 



