THE SENSE OF SMELL. 633 



The sense of smell is derived exclusively through those 

 parts of the nasal cavities in which the olfactory nerves 

 are distributed; the accessory cavities or sinuses com- 

 municating with the nostrils seem to have no relation to it. 

 Air impregnated with the vapour of camphor was injected 

 by Deschamps into the frontal sinus through a fistulous 

 opening, and Richerand injected odorous substances into 

 the antrum of Highmore; but in neither case was any 

 odour 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 vocalising. 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. 



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 

 second divisions of the fifth nerve. Hence the sensations 

 of cold, heat, itching, tickling, and pain; and the sensa- 

 tion 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 various 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 t?ie nose by acrid vapours, as of am- 

 monia, 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 vapours 

 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 



