62 
ANIMAL PATHOLOGY. 
of the aorta, and the bifurcation of the trachea. It is the 
source whence the heart derives the nervous influence that is 
bestowed upon it — it is the little brain of the heart. It is com- 
posed of the superior cardiac nerves on either side, derived from 
the superior cervical ganglion, and united to the cardiac branches 
of the great spinal organic as soon as they are given off. It 
also communicates with the recurrent nerve. The middle cardiac 
nerve, and the inferior one likewise, unite in the formation of this 
plexus or ganglion. This ganglion is an interesting object to 
the young anatomist, from its evidently being the centre whence 
proceeds all nervous influence to the heart. The nerves are 
beautifully traced from above : they enter into this expanded 
and pearl-coloured ganglion ; the plexus which they form is at 
first easily traced ; it is then lost in the substance of the gan- 
glion. Once more they assume their distinct corded form ; they 
escape from the lower part of the ganglion, and pursue their 
appointed courses. Some take a retrograde path to the pulmo- 
nary plexus ; others spread themselves over the aorta, and pene- 
trate the coats of that vessel : but the greater portion taking the 
direction of the coronary arteries, expand over every part of the 
heart, and, entering deeply into its muscular structure, finally 
spread themselves over the lining membrane of its cavities. 
The Cause of the Heart's Action . — What is the influence which 
this ganglion, with its peculiarly complicated structure, has on 
the action of the heart ? It is of complicated structure, for it is 
made up of branches derived from the great organic nerve, the 
ganglionic nerve, and the cerebro-spinal nerves, through the 
medium principally of the cervical plexus. The experiments 
that have been made by Braschet and others are very interest- 
ing, and, to a certain extent, satisfactory. The great spinal or- 
ganic nerve was divided above the origin of the cardiac branches, 
proper precautions being taken to prevent suffocation. There 
was immediate and very considerable disturbance of the action 
of the heart ; but in the course of an hour the animal was per- 
fectly tranquil, and the heart beat regularly. The first disturb- 
ance was a sympathetic effect — it was the consequence of pain ; 
and the pain subsiding, the regularity of the circulation returned : 
a sufficient proof that the influence of this nerve was not ne- 
cessary to the pulsation of the heart. To advert for a moment 
to other supposed sources of nervous influence : — the brain was 
entirely removed, but the heart beat on : the head was severed 
from the body, and, until all the blood had escaped, the heart 
continued to pulsate : the whole of the spinal marrow was de- 
stroyed — children have been born without the spinal marrow — 
and the heart has discharged its duty. 
