288 
OKI GIN AL ARTICLES. 
Pi g(Sus scrofa ), for example, they are well marked and easily distin¬ 
guished ; while in the full grown Eat {Mus decumanus ), I could detect 
no trace of their existence. I am, therefore, inclined to regard them 
merely as the result of the development of these organs, and not of 
any essential physiological import. It is to the anatomy of the 
commissure of the olfactory lobes, however, that I would chiefly direct 
attention. 
On examining the under surface of the brain of most mammalia, 
a band of white fibres will be seen running backwards and outwards 
from each lobe, and becoming lost in the grey substance of the brain. 
This, usually termed the “ root ” of the olfactory lobe, is simply the 
band of communication between the olfactory lobes and the cerebrum 
proper, and its function is evidently that of conveying the impressions 
made on the olfactory lobe to the grey matter of the brain. 
In the Eat these bands are very distinct, and terminate in the 
outer anterior portion of the cerebrum. Other fibres in connection 
with these lobes, however, will readily be found, and as they are 
most easily demonstrated in the above mentioned mammal, I will first 
describe them as they exist in that animal. On turning aside the 
white bands already described, and removing gently the grey matter 
from the inferior surface of the anterior third of the cerebrum, 
another series of white bands will be perceived as shown in Fig. 1. 
In order to obtain a clear view of all their relations, it will be neces¬ 
sary to remove the under surface of the olfactory lobes, and to clear 
away the greater part of the grey matter from the base of the brain, 
and to turn aside the optic tracts. The following will now be found 
to be the relation of the fibres referred to:—From the outer and an¬ 
terior part of each olfactory lobe will be found a small, well-defined, 
and round band of fibres passing backwards and inwards and uniting 
immediately posterior to the fissure between the olfactory lobes ; or 
perhaps it may be more correctly described as a band passing in a 
semicircular direction, the terminations of which are situated in the 
-outer anterior portion of each olfactory lobe. In the Eat this horse¬ 
shoe shaped band is about the size of fine sewing thread. It evidently 
constitutes the true commissure of the olfactory lobes. In favourable 
dissections a few fibres may be seen passing directly outwards from 
the convexity of the arch and terminating in that part of the cere¬ 
brum in which we find the superficial band of fibres connecting the 
olfactory lobes with the cerebrum to have their termination. 
From the inner and anterior portion of each olfactory lobe, a band 
of fibres arises and passes backwards through the structures at the 
base of the brain, the two bands slightly diverging from each other in 
their course. By a careful dissection these bands may be traced till 
they are lost in the anterior columns of the spinal cord. In the Pig 
the fibres above described present nearly the same relations as in the 
Eat, the only differences I could detect being the following:—1st. I 
could find no fibres passing outwards from the convexity of the 
olfactory commissure. 2nd. The bands of fibres passing between the 
