CHAP. XVI.] 



THE OLFACTORY REGION. 



We now come to the proper seat of the sense of smell, a com- 

 paratively limited district of the nasal organ, to which we shall apply 

 the term, olfactory region. As this olfactory region has not hitherto 

 been distinguished, nor its character understood, we shall describe 

 it somewhat minutely. This, as well as other parts, can be best 

 examined in animals, because they can be procured fresh and in a 

 state of health. The mucous membrane so soon loses many of its 

 most interesting features, especially where death has followed on 

 chronic disease, that the human subject is not the most favourable 

 for the investigation of its physiological anatomy, and can only be 

 advantageously inspected after the lower animals have furnished 

 the general clue. This remark is well illustrated by the present 

 instance. 



The olfactory region is situated at the top of the nose, immedi- 

 ately below the cribriform plate of the ethmoid bone, through which 

 the olfactory nerves reach the membrane; and it extends about one 

 third, or one fourth, downwards on Fig , 104 



the septum, and over the superior 

 and part of the middle spongy bones 

 of the ethmoid. Its limits are dis- 

 tinctly marked by a more or less rich 

 sienna-brown tint of the epithelium, 

 and by a remarkable increase in the 

 thickness of this structure, compared 

 with the ciliated region below; so 

 much so, that it forms an opaque 

 soft pulp upon the surface of the 

 membrane, very different from the 

 delicate, very transparent film of the 

 sinuses and lower spongy bones. The 

 epithelium indeed here quite alters " 



its Character, being nO longer ciliated, Vertical section of the olfaclory region of the 



, -IP f nose of the Rabbit : a. Surface of the epUhe- 



DUt Composed OI an aggregation OI Hum. b. Layer coloured by pigment, c. Line 



-, , , ., of basement membrane, d. Nucleated tissue 



Superposed nucleated particles, OI seen below, e. Olfactory nervous filament 



./, ,, , branching. Magn. 250 diam. 



pretty uniform appearance through- 

 out; except that, in many instances, a layer of those lying deepest, 

 or almost deepest, is of a darker colour than the rest, from the 

 brown pigment contained in the cells (fig. 104, b). These epi- 

 thelial particles, then, are not ciliated; and they form a thick, soft, 

 and pulpy stratum, resting on the basement membrane. The 

 deepest layer often adheres after the others are washed away. On 

 looking on the under surface of this epithelium, when it has been 



