viii SMELL 365 



both sides of the septum opposite to them, the mucous 

 membrane is specially modified, and receives the name of 

 olfactory mucous ' membrane ; and it is to this 

 olfactory mucous membrane that the filaments of the 

 olfactory nerve passing through the cribriform plate are 

 distributed. 



There is a third light scroll-like bone distinct from these 

 two, and attached to the maxillary bone, which is called 

 the inferior turbinal, as it lies lower than the other two, 

 and imperfectly separates the au* passages from the 

 proper olfactory chamber (Fig. 115). It is covered by 

 the ordinary ciliated mucous membrane of the nasal 

 passage, and receives no filaments from the olfactory 

 nerve. 



In the non-olfactory part of the nasal mucous mem- 

 brane the epithelium cells are ordinary ciliated epithelium 

 cells (see p. 286) ; but in the olfactory part the cells not 

 only lose their cilia, but become peculiarly modified. 

 Many of them become very slender and rod-shaped, and 

 the delicate terminations of the olfactory nerve filaments 

 appear to end in these modified epithelial cells, which 

 indeed are the sense-organules of the organ of smell. 

 The olfactory mucous membrane, with the filaments of 

 the olfactory nerve ending in it, thus constitutes the 

 essential part of the organ. 



The cells of the olfactory mucous membrane are of two 

 kinds, and somewhat similar to those composing a taste- 

 bud ; but their arrangement is different. Thus one kind 

 of cell is long, slender and rod-shaped, with a large 

 nucleus towards its inner end. The cells of the second 

 kind are also thin and rod-like at their inner ends, but 

 beyond the nucleus, the outer end is wide and columnar. 

 The cells of the first kind, which are the most numerous, 

 are supposed to be those which are specially concerned in 

 giving rise to the sensations of smell. The olfactory 

 mucous membrane is made up of a mass of these two kinds 

 of cell, placed side by' side and intermixed. (Fig, 117.) 



