406 
MR. YOUATT’s VETERINARY LECTURES. 
and then ramifies on the rhornboideus brevis, and vanishes in the 
substance of that muscle. 
An organic Motor Nerve .—The minute fibriculi from which it 
rises would create a suspicion that it is a motor nerve: the 
muscles on which it expends itself prove that it is so; and the 
lateral column whence it springs would indicate that it is em¬ 
ployed in the performance of some organic function. The muscles 
to which it is directed are voluntary muscles ; they are concerned 
in the motions of the head, the neck, and the fore extremities; 
they are supplied with nerves from the spinal chord, and which 
excite them to sufficiently powerful action for the purposes 
which they are to accomplish. They are voluntary muscles ; but 
they are also concerned, some of them at all times, and that in¬ 
voluntarily and unconsciously, in assisting in the function of 
respiration, and, when the breathing is hurried, they are all 
called into action consciously, yet, in a great measure, involun¬ 
tarily. This is plainly a respiratory nerve: it is concerned with 
the function of respiration alone, but respiration is one of the 
organic functions. I class it with the others as an organic motor 
nerve . 
The Twelfth or Phrenic Nerve .—We now leave the cranium 
and the spinal chord, and, observing the numerous ramifications 
and anastomoses of the cervical nerves, we find a very small one 
from the fifth (fourth) which takes its course down the neck, 
seemingly unconnected with any other nerve: we follow it, and 
it is joined by a branch from the sixth (fifth) cervical, and these, 
united, pursue the course which the first little filament had 
taken; and, by-and-by, these are associated with a branch from 
the seventh (according to the common nomenclature, the sixth) 
cervical nerve; and I have met with a filament from the lowest 
cervical nerve. The nerve thus formed, pursues its singular and 
solitary course down the remainder of the neck, and penetrates 
into the thorax, above the root of the axillary artery ; it enters 
the mediastinum, and proceeds on, attached to the outer side of 
the pericardium, a beautiful object to the young anatomist and 
even the experienced one; and it continues its lonely path until it 
reaches the diaphragm, which is its ultimate destination. It 
penetrates the pleura—its branches beautifully radiate for some 
distance over the diaphragm, and are then lost in the substance 
of that muscle. One branch, however, goes on from the right 
nerve,—the ramus anastomoticus—and contributes to form the 
semilunar ganglion. 
An organic Motor Nerve. —This is evidently an organic nerve, 
for it supplies the muscle mainly concerned in respiration. In 
its natural or relaxed state, the diaphragm bellies into the thorax. 
