390 
on the roof of the nasal cavity is 90p, of which 28y belongs to a 
superficial stratum formed by the cylindrical bodies of the ordinary 
epithelial cells (exclusive of their deep processes) and the intervening 
superficial processes of the olfactory cells 4, while the remainder of the 
height is occupied by a deep or nuclear stratum formed by the nu- 
merous (8 or 9) layers of olfactory cells. 
Structure of the lining membrane of Jacobson’s Organ. 
a. The Roof. Immediately within the osseous capsule which the Vomer 
forms for Jacobson’s Organ lies a somewhat scanty mucosa which is 
largely occupied by olfactory nerve-bundles: it is more richly pigmen- 
ted than the corresponding layer in the nasal cavity, its blood-vessels 
are of larger calibre, and it is destitute of Bowman’s glands. Most of 
the elements of the mucosa are continued inwards towards the lumen 
of Jacobson’s Organ between its cellular columns, which are thus iso- 
lated from each other by pigmentary connective-tissue and capillary 
vessels. Very few of the olfactory nerve-fibres appear to run in the 
partitions thus formed, the bundles entering the outer ends of the 
cellular columns almost entirely. ‘The capillaries arrived at the deep 
surface of the Neuro-Epithelium form there a plexus, the polygonal 
meshes of which are occupied by the inner ends of the cellular columns. 
This plexus obviously corresponds to that on which the neuro-epi- 
thelium ‘in the nasal cavity rests, buth there is no intervening base- 
ment membrane for a reason which will be presently apparent. ‘The 
neuro-epithelium (inside the plexus) is only 33p high, and the greater 
part of this belongs to the superficial stratum (as defined above) while 
only one or two layers of cells corresponding to the nuclear stratum 
are to be detected. These latter cells however, differ in form, accor- 
ding as they stand opposite a node or a mesh in the capillary plexus: 
in the former case they are shorter, and their deep processes are bent 
in such a manner as to pass round the vessel, in the latter case they 
are more fusiform, and they retain this shape for three or four layers 
while passing through the mesh into the corresponding cellu- 
lar column. With the exception of these spindle-shaped cells which 
form their inner ends the cellular columns are formed entirely of cells 
4 Although the cilia in the ordinary mucous membrane of the Nasal Cavity, 
and those on the floor of Jacobson’s Organ are well preserved in my preparations, 
I am unable to speak definitely of the structures outside the Memb. lim. olfact. 
either in the nasal cavity or in Jacobson’s Organ. 
5 Hoffmann (Chelonia p. 228) hesitates to describe the deeper cells of this 
stratum as olfactory cells. On the other hand Klein (lc. p. 565) and Retzius 
(Arch. Anat. Phys. 1880. I.) appear to have established in layers quite as thick that 
the superficial processes of the deepest cells do reach the surface. I have not con- 
vinced myself that such is the case here, and am inclined to doubt its possibility in 
the organ of Jacobson (vide infra). 
