THE SENSES. 



565 



{olfactory) cells, with both superficial and deep processes (Fig. 377), the 

 latter being probably connected with the terminal filaments of the olfac- 

 tory nerve. The lower, or respiratory part, as it is called, of the nasal 

 fossae is lined by cylindrical ciliated epithelium, except in the region of 

 the nostrils, where it is squamous. The branches of the olfactory nerves 

 retain much of the same soft and grayish texture which distinguishes 

 those of the olfactory tracts within the cranium. Their filaments, also, 

 are peculiar, more resembling those of the sympathetic nerve than the 

 filaments of the other cerebral nerves do, containing no outer white sub- 

 stance, and being finely granular and nucleated. The sense of smell is 

 derived exclusively through those parts of the nasal cav- 

 ities in which the olfactory nerves are distributed; the 

 accessory cavities or sinuses communicating with the 

 nostrils seem to have no relation to it. Air impreg- 

 nated with the vapor of camphor was injected into the 

 frontal sinus through a fistulous opening and odorous 

 substances have been injected into the antrum of High- 

 more; but in neither case was any odor perceived by the 

 patient. The purposes of these sinuses appear to be, 

 that the bones, necessarily large for the action of the 

 muscles and other parts connected with them, may be 

 as light as possible, and that there may be more room 

 for the resonance of the air in vocalizing. The former 

 purpose, which is in other bones obtained by filling their 

 cavities with fat, is here attained, as it is in many bones 

 of birds, by their being filled with air. 



Other Functions of the Olfactory Region. 

 All parts of the nasal cavities, whether or not they can 

 be the seats of the sense of smell, are endowed with com- 

 mon sensibility by the nasal branches of the first and sec- 

 ond divisions of the fifth nerve. Hence the sensations 

 of cold, heat, itching, tickling, and pain; and the sensation of tension or 

 pressure in the nostrils. That these nerves cannot perform the function of 

 the olfactory nerves is proved by cases in which the sense of smell is lost, 

 while the mucous membrane of the nose remains susceptible of the vari- 

 ous modifications of common sensation or touch. But it is often difficult 

 to distinguish the sensation of smell from that of mere feeling, and to 

 ascertain what belongs to each separately. This is the case particularly 

 with the sensations excited in the nose by acrid vapors, as of ammonia, 

 horse-radish, mustard, etc., which resemble much the sensations of the 

 nerves of touch; and the difficulty is the greater, when it is remembered 

 that these acrid vapors have nearly the same action upon the mucous 

 membrane of the eyelids. It was because the common sensibility of the 

 nose to these irritating substances remained after the destruction of the 



FIQ. 877. Epithe- 

 lial and olfactory 

 cells of man. The 

 letters are placed 

 on the free surface, 

 EE, epithelial cells; 

 Olf., olfactory cells. 

 (Max Schultze.) 



