744 



SPECIAL SOMATIC AND VISCERAL RECEPTORS 



receiving elements. This particular area occupies the nasal septum 

 and adjoining region of the superior turbinated bone, and measures 

 about 250 sq. mm. on each side. It is sharply differentiated from the 

 general lining membrane of this cavity by its yellowish brown color. 

 Each nasal cavity may be divided into two regions, namely, into 

 the so-called 'regio respiratoria and regio olfactoria. The former oc- 

 cupies the space between its floor, its median septum and the inferior 

 and middle turbinated bones. It receives its sensory nerve supply 

 chiefly from the second ramus of the fifth cranial nerve or trigeminus, 

 while its upper part is innervated by the first branch of this nerve. 



These fibers end free among the 

 lining cells and mediate general 

 sensations, namely, those of 

 touch, pain and temperature. As 

 such they may also be stimulated 

 by irritating emanations, such as 

 are derived from ammonia and 

 acetic acid. In this region are 

 also found numerous mucous 

 glands, while those in the upper 

 part of the nose are tubular. 



The olfactory regions proper con- 

 sist of non-ciliated columnar cells 

 which are intermingled with .a large 

 number of modified epithelial cells. 1 

 The free ends of these slender nerve cells 

 are beset with six to eight hair-like pro- 

 jections which extend through the limit- 

 ing membrane into the lumen of the 

 nasal cavity. Their basal portions are 

 directly continuous with the fibers of 

 the olfactory nerve, which pass through 

 the pores in the cribriform plate of the 

 ethmoid bone and eventually terminate 



in the olfactory bulb. They end here in 

 a, olfactory cells; o, epitnehal cells; n, , ,. ,, ,,. , ,. 



central process prolonged as an olfactory arborizations in the olfactory glomeruh 

 nerve fibril; I, nucleus; c, knob-like clear Lhe } T further course has been mapped 

 termination of peripheral process; h, olfac- out in one of the preceding chapters, 

 tory hairs. (After v. Brunn.) In the lowest vertebrates the olfac- 



tory organ appears in the form of a 



rounded or long drawn out depression, which is connected with the olfactory nerve. 

 In the selachiae, these grooves are connected with the cavity of the mouth by a 

 gutter-like prolongation. In the frog, this connecting passage is distinctly tubular. 

 The cephalopods are in possession of ciliated olfactory pockets which are situated 

 behind the eyes, while those of the arthropods are located upon the antennae. 



The Specific Action of the Olfactory Cells. The respiratory currents 

 of air traverse chiefly the lowest part of the nasal cavity, while the 

 air in its upper region remains practically stationary. From this it 



1 Pound in the frog by Eckardt in 1855, and in mammals by Ecker in 1856. 

 M. Schultze gave an adequate description of these Cells in 1863. 



FIG. 370. CELLS OF THE OLFACTORY 

 REGION. 



