THE NERVOUS SYSTEM 



245 



The nerves terminate in a kind of wreath formation about 

 the base of the vibrissae. 



All of these sense organs are invisible to the naked eye 

 except the Pacinian corpuscles. If the mesentery is held up 

 and looked through toward the light, the Pacinian corpuscles 

 or sensory nerve terminations appear as translucent oval bulbs 

 about two miUimeters long. If a piece of the mesentery con- 

 taining a corpuscle is pinned tense on a piece of cork and then 

 cut out and placed ten minutes in 3% 

 acetic acid, the termination of the nerve 

 wdthin the corpuscle may be seen with a 

 microscope magnifying thirty diameters. 

 All the spinal sensory nerve fibers enter 

 the cord by the dorsal root (Figs. 104 and 

 III). 



The Olfactory Organ. — The organ of 

 smell lies in that part of the mucous 



Fig. 



membrane lining the caudal part of the corpusc 



118. — Pacinian 

 :le from the 



nasal cavity and the basal third of the Mesentery, x 20. 



, , . 1 , /-r^. V rr^. OX, Axis-cylinder ; n, 



ethmoturbmal bones (Fig. I9J. That neurilemma; m, the 



part of the mucous membrane containing !?^f-^Y ^^J^^^^^' ^' ^^^" 

 the olfactory cells is known as the 



Schneiderian membrane. In a fresh specimen it is of a grayish 

 color while the other mucous membrane is red. The first 

 pair of cranial nerves convey the olfactory impulse to the brain. 

 They pass through the foramina in the cribriform plate of the 

 ethmoid bone, to the olfactory bulbs, from each of which 

 two roots extend to the base of the cerebrum (Fig. 104). 



The Gustatory Organ. — The organ of taste is located chiefly 

 in the mucous membrane on the dorsum of the tongue, the 

 soft palate, the pillars of the fauces, epiglottis, and part of 

 the cheek. On the dorsum of the tongue are seen four kinds of 

 papillae — the vallate, the fungiform, the filiform, and flat. The 

 vallate papillae are from eight to twelve in number, forming 

 two sides of a triangle on the caudal portion of the dorsum of 



