MINUTE ANATOMY OF NASAL MUCOUS MEMBRANE, 105 
The sensory cells vary much in size, some being nearly twice 
as bulky as others ; the latter possess also a larger nucleus than 
the former. They are generally arranged in a number of layers, 
five to twelve and more, either uniformly occupying the lower 
half or two thirds of the whole epithelium, or they form 
groups of four, five, and more. ‘There exists a great difference 
in different parts as regards the extent to which the sensory cells 
reach towards the surface, for there are many places in which 
only a narrow strip of 0°027 (the whole thickness of the epithe- 
lium being 0°1 mm.), z.e. only a fourth of the whole epithelium 
is free of them, while in other places they occupy a layer of 
0054 mm., or about one half of the whole epithelium. But it 
must not be therefore supposed that in the latter places the 
epithelial cells are much longer than in the former; this is 
not by any means the case; in the places where the sensory 
cells reach up near to the surface, the “ epithelial cells,’ if not 
wholly absent, are reduced in numbers to a very great extent, 
the outer processes of the sensory cells almost entirely occupying 
their places. Towards the sulcus, superior and inferior, the 
epithelium as a whole decreases in thickness; at the sulcus the 
epithelial cells become very few, and the sensory cells almost { 
entirely form the layer. There exists a most sharp boundary 
between the sensory epithelium and the ciliated columnar epithe- 
lium of the lateral wall, as mentioned above. The sensory 
epithelium at the extremities of the median wall is either rounded 
off, or it terminates with a pointed margin. On the free sues 
of the sensory epithelium is a delicate cuticle, similar to the cuti-' 
cle of v. Brunn, in the olfactory region. Both the processes of 
the sensory cells ana the basis of the epithelial cells appear to 
project over the cuticle, the former as a very minute rod-like, 
and the latter as a minute knob-like, homogeneous process. 
Amongst the lower layers of the sensory epithelium are seen 
either small bundles of nerve fibres, or isolated fine fibres, both 
extending in an oblique direction. The termination of the yy 
nerves has not been ascertained. = 
On the whole, then, this sensory epithelium corresponds to 
the olfactory epithelium, except that, in the latter, there exists a 
deep layer of inverted conical “‘ epithelial cells,” ¢.e. cells, whose 
bases are fixed on the subepithelial basement membrane. In the 
sensory epithelium of the organ of Jacobson this deep layer of 
inverted conical epithelial cells is apparently wanting, the sen- 
sory cells reaching as far down as the subepithelial fibrous coat. 
Besides, as mentioned above, the “ epithelial cells” of the sen- 
sory epithelium in the organ of Jacobson are much more in- 
distinct and smaller than those of the olfactory epithelium, 
