62 
MR. YOUATT’s VETERINARY LECTURES. 
first presents itself at the base of the brain, if we commence ante¬ 
riorly, is the olfactory nerve. It arises partly from the corpus 
striatum; but a medullary tractus, terminating in it, and evidently 
giving one origin to it, may be traced to the base of the corpus 
callosum. 
Its Character as a Nerve of peculiar Sensation. —Whether we 
trace its origin to the corpus striatum or the corpus callosum, it 
is derived from the superior portion of the medullary matter at 
the base of the brain—that which would be a continuation of 
the superior surface of the spinal chord if so far prolonged. If 
we follow its root to the corpus callosum the olfactory nerve 
is evidently referrible to the centre of that superior surface, and 
there is nothing inconsistent with the same derivation, when we 
attribute it to the corpus striatum. It proceeds in a manner 
bodily from the substance of the brain—it is an apparent pro - 
longation of the medullary matter of the brain. 
Comparative anatomists should not describe it as a mere 
mammillary process — u the ashen-coloured termination of the brain 
abutting upon the ethmoid bone.” Although the nervous chord 
is not separated from the brain 1o so great an extent as that of 
the optic or even the auditory nerve, and not nearly so much as 
we find it in the human subject, yet it has decidedly left the 
brain before it reaches the cribriform plate. 
Its course is short, and it has not a single anastomosis. I would 
beg you to pay attention to these peculiarities, these character¬ 
istics (as I shall by-and-by, be justified in calling them) of a 
nerve of peculiar sensation. Its minute ramifications, I have said, 
are affected only by the odoriferous particles of bodies. 
Size of the Nerve .—Observe the development of this nerve, 
bearing a beautiful proportion to the necessities of the animal. 
First, compare it with the same nerve in man—in him simply 
connected with pleasure—in the brute with life itself. In a brain 
not more than half the size of that of the human being, namely, 
the brain of the horse, the olfactory nerve is four times as large 
as in man. Compare its bulk in our different domesticated animals. 
In the horse it is large, for in a state of nature it affords his only 
warning against poisonous plants; but, almost all over the 
world, he has become our stabled servant, comparatively rarely 
sent to collect his own nutriment amidst the herbage of the field, 
and having the greater part of his food provided for him. The 
ox is oftener driven to shift for himself, or, if worked by day, he 
is usually turned out at night, and needs a somewhat acuter sense 
of smell. Observe, that although his brain is but little more 
than half the size of that of the horse, the olfactory nerve is nearly 
as large. In the sheep and swine it is comparatively as large as 
