i;74 HANDBOOK OF PHYSIOLOGY. 



into the frontal sinus through a fistulous opening and odorous substances 

 have been injected into the aiitruni of Highmore; 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 mus- 

 cles 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 vocaliz- 

 ing. The former purpose, which is in other bones obtained by tilling 

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

 by their being rilled with air. 



Other Functions of the Xasal J\t'<j'wn. All parts of the nasal cavi- 

 ties, whether or not they can be the seats of the sense of smell, are en- 

 dowed with common sensibility by the nasal branches of the tirst and 

 second divisions of the iifth 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 ol- 

 factory 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 and of 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 

 olfactory nerves that Magendie was led to the erroneous belief that the 

 fifth nerve might exercise this special sense. 



Varictie* of Oiluron* Sensations. Animals do not all equally perceive 

 the same odors; the odors most plainly perceived by an herbivorous ani- 

 mal and by a carnivorous animal are different. The Carnivora have the 

 power of detecting most accurately by the smell the special peculiarities 

 of animal matters and of tracking other animals by the scent; but have 

 apparently very little sensibility to the odors of plants and flowers. Her- 

 bivorous animals are peculiarly sensitive to the latter, and have a nar- 

 rower sensibility to animal odors, especially to such as proceed from 

 other individuals than their own species. Mail is far inferior to many 

 animals of both classes (which appear to have a special epithelial 

 arrangement called Jacobson's organ, for the purpose of "scent"), in 

 respect of the acuteiiess of smell ; but his sphere of susceptibility to various 

 odors is more uniform and extended. The cause of this difference lies 

 probably in the endowments of the cerebral parts of the olfactory appa- 

 ratus. The delicacy of the sense of smell is most remarkable; it can dis- 



