THE OLFACTORY NERVES. 
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is evidently proportionate to the wants, and to the kind of prey on 
which the different inhabitants of the waters are destined to feed. 
In the carp , the tench , and the barbie, they are comparatively 
small, and simple in their construction — their prey lies at the bot- 
tom of the river or pond, and is readily found. In the fresh-water 
shark — the pike — they are more complex, and almost equal the 
hemispheres in bulk. His destined victims can more readily escape 
from him, and he needs more powerful olfactory organs to scent 
them at a distance, and steal upon them unobserved. In the shark, 
the olfactory nerves are more than double the size of the hemi- 
spheres, for in the wide and trackless ocean he especially needs their 
power to guide him to his prey. I can scarcely give credence to 
the superstition of the sailor, who maintains than the shark will 
follow, for hundreds of miles, the vessel in which is a poor fellow 
rapidly approaching his end. This seems to be giving him a 
power of scent bordering a little too much on the marvellous ; yet 
perhaps you will hereafter listen to that thrilling song of “ the old 
admiral” with somewhat intenser interest, if that be possible. 
In the cetacea, the olfactory nerve is exceedingly diminutive. 
Cuvier says that it does not exist. The weight of authority, how- 
ever, is against him. In the greater number of the cetacea they 
can scarcely be mistaken, and in all they can be readily found ; but 
they do not communicate with the respiratory organs, or with the 
cavity of the mouth. They are merely blind sacs, with no other 
outlet than the external openings. If they were connected with the 
branchiae, through which the water is rushing at every expiration 
and inspiration, we should have difficulty in conceiving how the 
different effluvia could make the requisite impression ; but in these 
sacs the fluid, although continually changing, is sufficiently undis- 
turbed for them to have effect. 
The exit of the Olfactory Nerve from the Cranium. — Human 
anatomists, who assign to the olfactory nerve three origins instead 
of the one described by veterinary writers and the two of which 
I have ventured to speak, describe the compound nerve as leaving 
the mammillary process and expanding into an elongated bulb, 
whence filaments descend through the cribriform plate of the eth- 
moid bone : and they trace the fibriculi from the different origins 
to the different parts of the singular cartilage and bony compart- 
ments within the nasal cavity. I confess that I have never been 
able to do this in a way at all satisfactory to myself. I trace the 
compound nerve, covered with the arachnoid membrane and the dura 
mater, from under the mammillary process to the ethmoid bone. It 
is but a little space; but there is the actual structure of a nerve, be- 
tween the brain and this perforated bone. There is a distinct nerve; 
but there is no anastomosis, in order that the impression made on 
