176 HAND-BOOK OF PHYSIOLOGY. 



quick inspiration, assisted, as in the act of sniffing, by the action of the 

 nostrils, we render the impression more intense (see p. 201, Vol. I.). An 

 odorous substance in a liquid form injected into the nostrils appears in- 

 capable of giving rise to the sensation of smell: thus Weber could not 

 smell the slightest odor when his nostrils were completely filled with 

 water containing a large quantity of eau de Cologne. 



Seat of the Sense of Smell. The human organ of smell is formed 

 by the filaments of the olfactory nerves, distributed in the mucous mem- 

 brane covering the upper third of the septum of the nose, the superior 

 turbinated or spongy bone, the upper part of the middle turbinated bone, 

 and the upper wall of the nasal cavities beneath the cribriform plates of 

 the ethmoid bones (Figs. 354 and 355). The olfactory region is covered 



FIG. 354. Nerves of the septum nasi, seen from the right side. %. I, the olfactory bulb; 1, the 

 olfactory nerves passing through the foramina of the cribriform plate, and descending to be dis- 

 tributed on the septum; 2, the internal or septal twig of the nasal branch of the ophthalmic nerve; 3, 

 naso-palatine nerves. (From Sappey, after Hirschfeld and Leveille.) 



by cells of cylindrical epithelium, prolonged at their deep extremities 

 into fine branched processes, but not ciliated; and interspersed with these 

 are fusiform (olfactory) cells, with both superficial and deep processes 

 (Fig. 356), the latter being probably connected with the terminal fila- 

 ments of the olfactory nerve. The lower, or respiratory part, as it is 

 called, of the nasal fossae is lined by cylindrical ciliated epithelium, ex- 

 cept in the region of the nostrils, where it is squamous. The branches 

 of the olfactory nerves retain much of the same soft and greyish texture 

 which distinguishes those of the olfactory tracts within the cranium. 

 Their filaments, also, are peculiar, more resembling those of the sympa- 

 thetic nerve than the filaments of the other cerebral nerves do, contain- 

 ing no outer white substance, and being finely granular and nucleated. 

 The sense of smell is derived exclusively through those parts of the nasal 

 cavities in which the olfactory nerves are distributed; the accessory cavi- 

 ties or sinuses communicating with the nostrils seem to have no relation 



