448 



THE TISSUES. 



tion is unknown ; as is also that of the nervous filaments seen by 

 Eemak and Bochdalek, coming out from, and again re-entering the 

 brain. 



The three remaining encephalic nerves are nerves of special sen- 

 sation ; viz., the first pair (olfactory), the second pair (optic nerves), 

 and the eighth pair (acoustic). 



1. The first pair is the nerve of smell. The portion of this nerve 

 lying on the cribriform plate of the ethmoid, is called the bulb; and 

 the rest, extending from this to the cerebrum, the tract. Both these 

 are made up of the common dark-bordered nerve-fibres. 



The branches, on the other hand, which are given off from the 

 bulb into the upper portions of the nasal passage (Fig. 290), con- 

 tain no white medullated fibres at all; but are constituted of pale, 

 slightly granular, flattened fibres (Fig. 291, 6), 6 oVo to Wuu ^ an 

 inch wide, with elongated nuclei retained closely in connection by 

 common sheaths of connective tissue, which are thicker in the 

 branches to the septum. (Fig. 292.) In the bulb, however, nerve- 



Fig. 292. 



Fig. 291. From the nasal mucous membrane of the sheep. 1. From the regio olfactoria, trans- 

 verse section of the mucous membrane ; a, epithelium without cilia ; &, olfactory nerves, with a 

 dividing pale nucleated fasciculus ; c, one of " Bowman's glands ;" d, its orifice. 2. Ciliated epi- 

 thelium of the Schneiderian membrane. Magnified 350 diameters. (Ki'lliker.) 



Fig. 292. Nerves of the septum of the nose. a. Olfactory bulb resting on the cribriform plate, 

 below which its branches may be traced on the septum about half way down. Behind, the naso- 

 palatine nerve from Meckel's ganglion is seen descending to the naso-palatine canal. In front, the 

 nasal twig of the ophthalmic nerve descends towards the tip of the nose, dividing into two principal 

 branches, p. Roof of the mouth, e. Orifice of the Eustachian tube. Magnified one-half diameter. 

 (Arnold.) 



