SENSE OF SMELLING. 
71 
The Olfactory Nerves .—The olfactory, or first pair of nerves, 
have a double origin, viz. from the corpus striatum, and the base 
of the corpus callosum. They seem to be prolongations of the 
medullary substance of the central portion of the brain. They 
are the largest of the cerebral nerves. Compare their develop¬ 
ment with that of the olfactory nerves of the human being. There 
is a remarkable difference, but not more so than in function ; for 
in the one they are connected with pleasure and in the other with 
life. Their course is short, exceedingly so ; and they have not a 
single anastomosis, in order that the impression made on them 
may be conveyed undisturbed and perfect to the brain. 
The olfactory nerve is a prolongation of the substance of the 
brain, and it abuts on the cribriform plate which I have de¬ 
scribed. I will not speak of the singular cavities which it con¬ 
tains, nor of their function ; this belongs to the sensorial system : 
but it is in contact with the thin perforated plate of bone occupy¬ 
ing the chasm between the base of the aethmoid bone and the 
frontals, and is in a manner pressed through this cullender-form¬ 
ed plate, and its pulpy matter is clearly to be traced over the 
upper part of the septum, and over a part of the superior turbi¬ 
nated bone. Although we soon lose it in the mucous membrane 
of the nose, we think we are warranted in concluding, that in a 
more filmy form it is spread over the whole of the cavity, and 
probably over all the sinuses of the face and head. It is, how¬ 
ever, so mingled and incorporated with the mucous membrane, 
that no power of the lens has enabled us to follow it so far. It 
is like the portio mollis of the seventh pair, eluding the eye, but 
existing in sufficient substance for the performance of its impor¬ 
tant function. 
An acute sense of smell is necessary to the quadruped. Every 
plant has its peculiar scent, and probably a scent of a marked 
character as connected with nutrition or destruction. We find 
out something of this by experience; the brute learns it from 
mingled experience and instinct. Without instruction and with¬ 
out experience, the beast has generally some salutary warning to 
guide him to that which is nutritive, and to warn him from that 
which would be poisonous. He is, however, sometimes deceived ; 
but that is only in the early part of the spring, when the scent of 
the infant plant is not developed. Horses at grass are frequently 
ill at that time, and cattle more seriously so, and, occasionally, 
they are actually poisoned. When the great Linnaeus visited 
Tornea, the inhabitants complained of a distemper which killed 
many of their cattle, and especially when first turned out into the 
meadows in the spring. He soon traced the disorder to the water 
hemlock, which grew abundantly there, and which in the spring 
