v///: r/.MY/.i/. <>i; /;v /;///.!/./ XKIU'ES. 705 



, has its source in a misunderstanding, and is really not founded on 

 . which a iv tin s.imc for everyone, their appreciation only varying. 

 Nothing is more easy to prove. Look, in the first instance, at the optic 

 nerve. This, according to some, proceeds from the corpora quadrigemina 

 and tlmlami optici ; it therefore arises from the brain. No doubt, if these 

 two parts of the enct-phalon bo considered as a portion of the hemispheres; 

 but this is far from proved, and in an anatomical and physiological point 

 of view it is not so. As tho corpora quadrigemina and thalami optici form 

 part of the isthmus, it is natural to look upon it as the source from which 

 tin- second pair of nerves arise. With regard to tho first pair, their fibres 

 Iso connected with those of the isthmus, across the corpus striatum, as 

 will be proved hereafter. But we are far from denying their connections 

 with the hemispheres (see the description of the first pair), and which are 

 very intimate ; though this proves nothing against our opinion. Therefore 

 it is, that, in recognising in the disposition of the roots of the olfactory 

 conditions altogether special, we admit that the isthmus of the 

 encephalon is the common point of departure for all the cranial nerves an 

 important and capital fact, and which constitutes, for the great category of 

 encephalic nerves, a true family character. 



Among the other points relative to the origin of these pairs of nerves, 

 the following: All the encephalic nerves appear to be connected at 

 their origin with the fasciculi of the isthmus, whose properties they share. 

 All tire equally connected with a centre of grey substance placed in the 

 texture of the isthmus, and named by Stilling the nucleus of the nerves. 

 The majority originate by converging filaments, the anterior of which come 

 from the brain, and the posterior from the side of the spinal cord. 



l'i-i-paration of the cranial nerves. Four preparations are necessary to study the 



cranial in 



1. An encephalon extracted after opening the cranium by its base, and hardened 

 by prolonged immersion in alcohol or very diluted acetic acid. Thin piece permits the 

 origin of the nerves to l.e >tndied (Kiir. 322). 



1 In- Mi|H-itieiul nerves i 'f the h ail: these lire the auricular nerves, and tho 

 division.-. of the .-nh/ygomatic plexus, with the suborbital and mental branches, as well 

 rtirial rniiiuscules of the thn n.-rvrs of the ophthalmic branch of the fifth 

 1 i- 110). 



l>osed as in figure 336, for the study of the maxillary nerves. To prepare 

 it. tin- great ; muscle should ' removed in di.-* oting the masseteric 



extirpated, tin orbital and /ygoniatie processes 



maxillary .-inuscs opened, and the branch of the inferior maxillary bone 

 led otV as in tin- figure. Lastly, the an: t the lacial with the sub- 



ii'-rve i.- <li-- et- .1 I'V rutting away tin; parotid glnnd. 



I he deep nerves, including those ot'tl.c globe of the eye : this preparation should 

 be made by following . \a tiy the in-trm-iions given for dissecting the arteries of the 



Figure ::::."> will serve as a guide lor details. 



The pneiimogastric and spinal nerve.--, which are not included in these considerat 

 -li-iiM l>e prepared and studied at the same time as the great sympathetic. When 

 treating of the latter, we will refer to them. 



1. First Pair, or Olfactory N> rrcs. (Figs. 327, 329.) 



Tho first cranial pair is constituted by the olfactory lobes, whose 

 or extremities give off a great number of nervous filaments, which pass 

 :_'h tin- cribriform foramina to ramify in that part of the pituitary 

 membrane lining tho bottom of the nasal fossae. 



Kaeh olt.c-t'.ry lobe is connected with the enceplialon by t\\. rm.N. an 

 nal and an internal, l>oth composed of white subsUiin i 



