632 MR. youatt’s veterinary lectures. 
nearly its former bulk. These, from their kind and place of 
origin, we should suspect to be nerves of sensation. Then, and 
still within the dura mater, or at the moment of escaping from it, 
the two chords unite, and form a perfect but compound nerve ; 
of which I shall say no more at present, than that it is what we 
suspected it to be—that it combines the properties it derived 
from these central columns on the inferior and superior surfaces 
of the spinal chord, and is a nerve of sensation and voluntary 
motion. It is distributed to the neighbouring parts, and it anas¬ 
tomoses with those above and below, for important purposes, 
which will be the subject of future consideration. At each ar¬ 
ticulation of the cervical, dorsal, and lumbar bones, as we pro¬ 
ceed along the spine, we find one of these compound nerves. 
Towards the lower part of the neck, we observe filaments from 
the fourth, fifth, and sixth cervical nerves, uniting to form a 
singular nerve, which takes its course down the neck, without 
anastomosis, and traverses the chest, and ramifies upon the 
diaphragm. This phrenic nerve is the motor nerve of the dia¬ 
phragm, the grand agent in respiration, and, therefore, we have 
no difficulty in denominating it an organic motor nerve, I shall 
have to shew, that it is not improbable, that although the fila¬ 
ments which compose it are derived from the cervical nerves, yet 
they may actually have their origin from that portion of the 
spinal chord which seems to be devoted to the purposes of organic 
life. 
The dorsal, lumbar, and sacral nerves, have the same struc¬ 
ture, and discharge the same function. They are all nerves of 
sensation and voluntary motion; and those of the extremities, 
derived from plexuses of the cervical and the dorsal, and the 
lumbar, and the sacral, possess fhe same character. 
The Ganglial Nerve. —There is one nerve wanting to com¬ 
plete our list: it belongs neither to the cerebral nor the spinal 
system, and seems in its function to be independent of both. At 
the base of the cranium, and in front of the atlas, I find a pyri¬ 
form reddish body, which gradually contracts, and terminates 
in a nerve. I inquire not now into the origin of this ganglion, 
but a superficial glance at the nerve tells me that it is performing 
some important office. It is connecting itself with the cerebro¬ 
spinal, and with every cervical nerve ; but more particularly it is 
forming complicated plexuses on every neighbouring bloodves¬ 
sel. I trace it particularly on both the external and the internal 
carotid, and I follow it in the subdivisions of these vessels, until, 
from the minuteness of the vessel and the pulpiness of the nerve, 
it eludes my sight. Hereafter I shall have to trace the course 
of the nerve in the thorax, forming, with the cerebro-visceral, a 
