676 



Comparative Morphology of Chordates 



rrPrrr 



Fig. 506. The olfactory organ of man. (A) Right nasal cavity, with the nasal 

 septum turned up along its superior border. The olfactory area is indicated in black. 

 (After Read.) (B) Section of the olfactory mucous membrane prepared by the 

 silver technic. The olfactory cells and fibers are in black. (X 550.) (C) Isolated 

 elements of the olfactory epithelium. The olfactory cells bear fine "hairs" re- 

 sembling cilia. (X 735.) (After Brunn.) (Courtesy, Jackson: "Morris' Human 

 Anatomy," Philadelphia, The Blakiston Company.) 



turbinate are relatively narrow and convex upward, but are not rolled 

 into actual "scrolls." Of the three adult turbinals, usually only the 

 upper of the two ethmoturbinals is olfactory and only a part of its 

 surface is occupied by olfactory cells. Also, the adjacent upper region 

 of the nasal septum is olfactory. The total olfactory area for the two 

 human nasal cavities has been estimated at from 5 to 12 square centi- 

 meters, which is a small part of the nasal surface. The higher estimates 

 are probably more nearly correct. 



The human olfactory surfaces are so restricted to the posterodorsal 

 region of the nasal cavity that they are out of the main part of the 

 respiratory current. During ordinary easy breathing, the presence of 

 an odorous substance in the air may not be noticed, but a forcible 

 snuffing, drawing more air up into the olfactory region, may reveal it. 

 Dogs and other mammals may be observed now and then snuffing 

 in air. 



The turbinals are important quite aside from their olfactory func- 

 tion. They are an "air-conditioning" apparatus. Their investing mem- 

 branes are highly vascular. Hence the surfaces are warm. Glands keep 

 them covered by a layer of moisture. On its way through the nasal 

 labyrinth, the inhaled air (if cool) is warmed and moistened, thus 

 becoming adapted to reception by the lungs. Also, the mucus-covered 

 surfaces serve to screen out solid impurities from the air. Every person 



