SENSATION OF SMELL. 



respiratory regions are as follows: (i) The olfactory region possesses a thicker 

 mucous membrane; (2) it is covered with a single layer of cylindrical epithelium, 

 0.06 mm. thick (Fig. 329, E), the branched basal portions of which often contain 

 a yellow or brownish-red pigment (denser in animals), while the respiratory 

 region has a double layer of ciliated epithelium, mixed with goblet-cells; (3) 

 the olfactory region is, therefore, distinguished by the coloration mentioned; (4) 

 it contains peculiar club-shaped tubular glands (the glands of Bowman), which are 

 considered mucous glands, while the respiratory portion contains principally 

 acinous glands. According to A. Heidenhain, the latter are serous, according 

 to Stohr (in man) mixed glands. Lymph-follicles are found in the mucosa be- 

 neath the epithelium, and from them numerous leukocytes make their way on to 

 the free surface. (5) Finally, the olfactory region contains the end-organs of 

 the olfactory nerve. The olfactory cells (N) lie scattered between the long, 

 cylindrical epithelial cells (E) of the surface. A spindle-shaped cell-body, with a 

 nucleus and large nucleolus sends upward, between the cylindrical cells a smooth 



Rip. 



P.S.JI h 



FIG. 329. N, Olfactory FIG. 330. Nasal Cavity and Nasopharynx: L, levator 



cell from man (the pad; p^ p salpingopalatine fold; P.s.ph., salpingo- 



hairs have fallen off); pharyngeal fold; Cs, Cm, Ci, the three turbinates 



n '-l r Ti ii r g ] ' (Urbantschitsch). 



epithehal cell from 

 the olfactory region. 



rod, from p. 9 to 1.8 //thick, from the extremity of which from 6 to 8 fine olfactory 

 hairs project through the pores of a delicate, structureless limiting membrane 

 covering the surface of the epithelium. The olfactory cells become continuous 

 with fine varicose nerve-fibrils in the depths of the mucosa, and these pass into the 

 olfactory nerve. According to C. K. Hoffmann and Exner, after section of the 

 olfactory nerves in frogs the specific end-organs are converted into a nonciliated 

 cylindrical epithelium, while in warm-blooded animals they undergo fatty de- 

 generation; but, at the same time, the epithelial cells between them exhibit 

 signs of degeneration. 



The olfactory cell of the olfactory region is a ganglion-cell whose neuron is 

 represented by a nerve-fiber, which enters the olfactory bulb. The telodendrites 

 neurons come in contact within the spherical glomeruli with dendrites from 

 ganglion-cells of the bulb Passing through further layers of the bulb (gelatinous 

 olffin Y t r t P yTam * d * 1 C 1 f lls ' g^nular layer) the origin of the fiblrs in the 

 ^factory tract is reached, the course of which is described on p. 678. 



, SENSATION OF SMELL. 



The sensation of smell is brought about by the action of odorous 

 substances in a gaseous state, which come in direct contact with the 

 )lfactory cells, especially in their passage through the nares during 



