146 COMPARATIVE ANATOMY AND PATHOLOGY. 
life — and, finally the fifth, a nerve both of sensation and of volun- 
tary motion as it regards the face — and the spinal nerves, executing 
the same double office over the remaining part of the frame — of 
these animal nerves sufficient has been said. There now remain 
three nerves belonging to the animal system, and especially con- 
necting us with the objects around us — nerves of pure and peculiar 
sensation ; the first, or olfactory nerve, responding only to the 
impression made by the odoriferous particles of bodies ; the optic 
nerve, affected only by the particles of light ; the auditory, which 
is sensible only to the vibrations of the air. 
The first of these has already been treated of, in the beginning 
of the fifth volume of The VETERINARIAN ; therefore my present 
remarks on it shall be brief, and consisting chiefly of new views 
that have presented themselves to my mind in the last seven years. 
The origin of the Olfactory Nerves. — If here I venture to differ 
from some of the anatomical writers in my own profession, as well 
as from the human anatomist, I do so with diffidence, and should 
rejoice to be set right. In the first place, I must deny one origin 
of this nerve from the under surface of the corpus-striatum. I can 
trace one of the origins of the olfactory, with my friend Mr. Percivall, 
“ along the posterior borders of these bodies, as high up as the 
middle lobes of the cerebrum,” and until I lose them in the medul- 
lary substance of the brain ; but not in any portion of the corpus 
striatum, properly speaking. Beside this, I have on the under 
surface of the anterior lobe of the brain, on either side, another 
evident root or source of this nerve, namely, the corpus callosum ; 
and there, again, I lose it in the medullary substance of the brain. 
It is a prolongation of that medullary substance. On the other 
hand, I have not been able to find in any of our patients the treble 
origin of this nerve, of which most of the modern human anatomists 
speak. I can trace their second root to the corpus callosum, con- 
tinuous with the substantia perforata, or lamina cibrosa ; but I 
cannot find the third source in the extremity of the groove which 
contains the second root. 
Their course. — We trace these roots along either side of the ante- 
rior lobe, until we are approaching the mammillary processes. Each 
of them is securely lodged in a groove, into which one of its edges 
(for it is of a triangular form) penetrates ; while its exterior and 
flattened surface is covered by the arachnoid membrane. 
Structure. — They are apparently of a medullary consistence. 
They are the softest in their texture of any of the nerves of the 
brain ; but the minute fibrillse of which they are composed are 
readily detected by the aid of a microscope. In all our patients 
the olfactory nerve is hollow. It communicates, posteriorly, with 
the anterior cornu of the lateral ventricle ; but before it reaches 
