OLFACTORY EPITHELIUM. 



is into a ciliated crypfc. Here and there the epithelium of the surface, as shown by 

 Max Schultze, is ciliated and not olfactory ; where this is the case, the ordinary 

 racemose glands are found (Klein). On the other hand, Bowman's glands are not 

 entirely confined to the olfactory mucous membrane, but may extend a short 

 distance beyond it into the respiratory part of the fossa. 



The columnar cells on the surface of the olfactory mucous membrane (fig. 159, a) 

 are prolonged at their deep extremities into a process which is generally somewhat 



Fig. 159. CELLS OF THE OLFACTORY REGION. (M. Bchultze.) 

 Highly magnified. 



1, from the frog ; 2, from man ; a, epithelial cell, extending deeply 

 into a ramified process ; 6, olfactory cells ; c, their peripheral pro- 

 cesses ; e, their extremities, seen in 1 to be prolonged into fine hairs ; 

 d, their central filaments. 



branched towards its deeper end. The nuclei of these 

 cells are oval in shape and lie all at about the same level 

 (zone of oral nuclei), i.e., in the deeper part of the 

 columnar portion of each cell. The protoplasm of the 

 columnar cells contains granules of yellowish-brown pig- 

 ment. Amongst the branching central ends of these 

 columnar cells there are a large number of peculiar 

 spindle-shaped cells (fig. 159, #), each consisting of a 

 large, clear, nearly spherical, nucleus surrounded by a 

 relatively small amount of granular protoplasm. From 

 each cell proceeds a superficial and a deep process. The 

 superficial process (c) is a cylindrical or slightly tapering- 

 thread passing directly to the surface, and terminating 

 abruptly at about the same level as the free surface of 

 the epithelial cells between which it lies, or a little 

 beyond ; the deep process (d) is more slender, and passes vertically inwards. This 

 last usually presents a beaded appearance similar to that observed in fine nerve- 



Fig. 160. AN OLFACTORY CELL, HUMAN. (v. BlTinn.) 



n, central process prolonged as an olfactory nerve fibril ; b, body of cell with nucleus ; 

 p, peripheral process passing towards free surface ; c, knob-like clear termination of 

 peripheral process ; A, bunch of olfactory hairs. 



filaments. These cells were termed by Max Schultze, olfactory cells, 

 to distinguish them from the columnar epithelium cells, which are much 

 fewer in number, and which are entirely surrounded with the fine 

 rod-like peripheral processes of the smaller cells. The nucleated bodies 

 of the olfactory cells are several rows deep, and form a layer of 

 considerable thickness beneath the columnar cells (zone of round nuclei). 



In the rabbit and guinea-pig Klein, in confirmation of a statement 

 by Sidky, describes a lowermost layer of conical vertical cells resting 

 by their bases upon the membrana propria. 



The total thickness of the olfactory epithelium in man is 0'06 mm., 

 whereas in macrosmatic mammals it is O'l mm. or more (v. Brunn). 



The olfactory (but not the columnar) cells are said to project 

 through apertures in a cuticular lamina which bounds the mucous 

 membrane superficially (external limiting membrane, v. Brunn). The 

 existence of this cuticle has been, however, called in question by other 

 observers. 



The peripheral process of the olfactory cell was observed by Schultze to be 



