262 
ANIMAL PATHOLOGY. 
lie says that “ along the lateral aspect of the cord a slightly de- 
pressed line may be traced down as a continuation of that which 
separates the corpus restiforme from the olivare, gradually how- 
ever becoming more faint, and ceasing to be perceptible about 
the upper part of the dorsal region.” 
Whatever difficulty there may be in the anatomical proof of 
the existence of this track of organic nervous power, there are 
many physiological facts which can be explained solely on the 
supposition of its existence. The organic power of the respi- 
ratory portion of the seventh pair, and of the par vagum, have 
been sufficiently illustrated. We proceed a little way down the 
cord. 
The Spinal Accessory Nerves arise from several filaments 
springing plainly and evidently from the lateral portion of the 
spinal cord — the continuation of the line occupied by the organic 
nerves already considered. As soon as a few filaments have unit- 
ed to form a nerve, it ascends between the sensitive and motor 
portions of the superior cervical nerves, and enters the cranium, 
and comes in contact with the great spinal nerve, and issues from 
the same foramen with it, and, after numerous anastomoses with 
other nerves of common sensation and motion, it distributes it- 
self, and is lost on the mastoid and trapezius muscles. These 
muscles are principally voluntary ones — they are concerned with 
the motions of the head and neck and fore extremities, and they are 
supplied with nerves from other sources which endow them with 
this voluntary power. But they are wanted when the animal is 
unconscious of their action ; they are wanted still more in hurried 
breathing, and then they act involuntarily : they become devoted 
to the purposes of organic life, and they afford a striking illustration 
of the excito-motory system of Dr. Marshall Hall. Sir Charles 
Bell put the real function of these nerves fairly to the test. He 
divided the fibres from the lateral face of the spinal cord, 
and these were no more organic, but simple voluntary muscles. 
Excited respiration was produced in an ass, and these muscles 
were brought into powerful action in combination with the other 
muscles of respiration : while this was performing, the nerve was 
divided — the motion ceased, and the muscle remained relaxed, 
until the animal brought it into action as a voluntary muscle. 
Here, then, is evidently a source of organic power either superfi- 
cially or deeply seated. 
The Phrenic Nerve . — The upper fibres which go to form this 
nerve proceed from the same distance down the cord with the 
lower ones that went to form the spinal accessory, but from dif- 
ferent columns — no longer from the lateral surface, but from the 
columns of sensation and voluntary motion. As the nerve pro- 
