NERVOUS SYSTEM. 63 
in the ox, or even more so ; and in the dog you cannot fail of 
remarking its still greater comparative bulk. 
Peculiarities about it.— The olfactory is, next to the fifth, 
the largest of the cerebral nerves, and it is the softest in its tex¬ 
ture ; nevertheless its fibrous structure has been demonstrated, 
and it is the excessive looseness and thinness of the neurilema 
that gives it its pulpy appearance. It has a singular cavity in it, 
the use of which I am unable to state. That cavity is a prolon¬ 
gation of the anterior cornu of the lateral ventricle ; it terminates, 
however, in a blind pouch before the nerve reaches the ethmoid 
bone, and there is consequently no channel by which, as was 
formerly supposed, any fluid can be conveyed from the brain 
into the nose. 
Termination. —In company with, and under the real mammillary 
process, it abuts upon the cribriform or thin perforated plate of 
the ethmoid bone, and sends its pulpy fibres through it. These are 
visibly spread over the upper part of the septum and superior 
turbinated bone, and which probably extend over the whole of 
the nasal cavity : of this, and of the sense of smell, I have already 
spoken when treating of the respiratory system. 
The Olfactory Nerves in Birds. —In our occasional patient, 
the feathered biped, the olfactory nerve comes nearer to a 
mammillary process, for it arises from the very point of the anterior 
termination of the brain, and seems to be a mere continuation of 
it. Having left the cranium, it enters into a bony canal, and so 
passes through the orbit which interposes; and it is finally 
distributed, not on the ethmoid bone, for that is in a manner 
wanting in the bird, but on the pituitary membrane covering the 
superior concha of the nose. 
The Optic, or Second Pair of Nerves.— On the crura cerebri, 
when they first appear at the base of the brain, there are seen two 
prominent medullary chords winding their way over the crura 
in a direction inwardly and anteriorly. They first emerge from 
under the hemispheres, opposite to the corpus albicans, and they 
meet each other immediately anterior to the infundibulum and 
the pituitary gland. 
Their Character as Nerves of a peculiar Sensation. —The 
medullary chords of which I have just spoken—the tractus 
optici —can be traced to the thalami nervorum opticorum in the 
centre of the brain; they are, in fact, a continuation of the 
thalami ; or the thalami contract, and are prolonged into these 
medullary chords. I have also said that they are connected by 
medullary striae with the corpora quadrigemina, and particularly 
with the nates. Now the thalami and the nates evidently 
occupy that port ion of the base of the brain which would cone- 
