SPECIAL SENSES 



The essential organ of olfaction is the mucous membrane lining the 

 upper half of the nasal fossae. Not only has it been shown anatomi- 

 cally that this part alone receives the terminal filaments of the olfactory 

 nerves, but experiments have demonstrated that it is the only part capa- 

 ble of appreciating odorous impressions. If a tube is introduced into 

 the nostril, placed horizontally over an odorous substance so that the 

 emanations can not penetrate its calibre, no odor is perceived, though 

 the membrane below the end of the tube might receive the emanations ; 

 but if the tube is directed toward the pdorous substance, so that the 



emanations can pene- 

 trate to the upper por- 

 tion of the nares, the 

 odor is immediately 

 appreciated. 



That portion of the 

 lining of the nasal 

 fossae, properly called 

 the olfactory mem- 

 brane, extends from 

 the cribriform plate 

 of the ethmoid bone 

 downward a little less 

 than an inch (25 milli- 



Fig. 156. Olfactory ganglion and nerves (Hirschfeld). meters). It is Soft and 



i, olfactory ganglion and nerves ; 2, branch of the nasal nerve; friable, Very Vascular, 



3, spheno-palatine ganglion; 4, 7, branches of the great palatine .u: p i, pr 4-U an t u p 



nerve; 5, posterior palatine nerve; 6, middle palatine nerve; 8,9, U11LK( 



branches from the spheno-palatine ganglion; 10, n, 12, Vidian of the 

 nerve and its branches ; 13, external carotid branch from the supe- , , . 



rior cervical ganglion. membrane, and in man 



it has rather a yellow- 

 ish color. It is covered with long, delicate, columnar cells, nucleated, 

 and each one provided with three to eight ciliary processes, the move- 

 ments of which are from before backward. The olfactory membrane 

 is provided with a large number of long racemose mucous glands, which 

 produce a secretion that keeps the surface moist, a condition essential 

 to the accurate perception of odorous impressions. The olfactory organ 

 in some of the lower animals, in which the sense of smell is very delicate, 

 is relatively larger than in man. In dogs it is much larger. 



OLFACTORY (FIRST NERVE) 



The apparent origin of the olfactory nerve is by three roots from 

 the inferior and internal portion of the frontal lobe of the cerebrum, in 



