566 ; DR. E. KLEIN. 
the organ of Jacobson of the guinea-pig, and I have there also 
referred to the assertions and observations on these points by 
Balogh! in the sheep’s organ, so that it is needless to enter into 
this subject here again. 
In the rabbit’s organ I have been able to follow what at first 
I omitted to do in the guinea-pig’s organ, but what I have now 
done also in this last named animal, viz. the distribution of the 
olfactory nerve bundles and nerve fibres in the median wall, and 
their relation to the sensory cells. 
All along the inner surface of the median labium of Jacobson’s 
cartilage we find olfactory nerve bundles following a longitudinal 
direction ; spreading from behind toward the anterior regions of 
the organ of Jacobson,” it is natural that we should find the 
number of nerve bundles greater in the posterior than in the 
anterior regions of the organ. 
The transverse diameter of a large nerve bundle in the anterior 
portion of the organ is about 0°144 by 0°216 mm. From these 
nerve bundles, which, as mentioned just now, run in a longitu- 
dinal direction in the outer parts of the mucosa of the median 
wall, z.e. near Jacobson’s cartilage, numerous minute bundles 
branch off, which run in an oblique direction towards the sensory 
epithelium; they are very numerous, and by branching and re- 
uniting form a plexus of small bundles of olfactory fibres occu- 
pying the inner part of the mucosa of the median wall. The 
nearer the sensory epithelium the smaller the branches and the 
closer the plexus. This plexus, subepithelial plewus, extends 
pre-eminently in a direction parallel with the short axes of the 
organ of Jacobson. The ground substance of the mucosa in 
which this plexus is embedded is made up of fibrous connective 
tissue. The relation of this plexus to the sensory cells is this: 
those sensory cells which, as mentioned above, extend into the 
mucosa, are situated in the meshes of the plexus, but are very 
closely applied to the branches of it, and from what I have been 
able to make out in thin sections appear to become continuous 
by their deep process with the nerve fibres in such a way that the 
process constitutes a primitive fibril of an axis-cylinder of the 
nerve branch. 
Yn the sensory epithelium the sensory cells appear all to be 
contained in the meshes of a plexus of fibrillar bands, which appear 
directly continuous with the branches of the subepithelial nerve 
plexus. As is the case with the sensory cells extending into the 
mucosa, so also with the other sensory cells, it can be ascertained 
that with their deep process or processes they join as primitive 
1 L.c., pp. 465 and 466. 
2 See Gratiolet and Balogh on the general distribution of the olfactory 
nerve brauch. 
