n the striking of the tendon and the
jerk. The presence or absence of the knee-jerk may be a most significant
symptom to the physician.

282. The Sympathetic System. Running along each side of the spine,
from the base of the skull to the coccyx, is a chain of nerve knots, or
ganglia. These ganglia, twenty-four on each side, and their branches
form the sympathetic system, as distinguished from the cerebro-spinal
system consisting of the brain and spinal cord and the nerves springing
from them. The ganglia of the sympathetic system are connected with each
other and with the sensory roots of the spinal nerves by a network of gray
nerve fibers.

At the upper end the chain of each side passes up into the cranium and is
closely connected with the cranial nerves. In the neck, branches pass to
the lungs and the heart. From the ganglia in the chest three nerves form a
complicated network of fibers, from which branches pass to the stomach,
the liver, the intestines, the kidneys, and other abdominal organs. A
similar network of fibers is situated lower down in the pelvis, from which
branches are distributed to the pelvic organs. At the coccyx the two
chains unite into a single ganglion.

Thus, in general, the sympathetic system, while intimately connected with
the cerebro-spinal, forms a close network of nerves which specially
accompany the minute blood-vessels, and are distributed to the muscles of
the heart, the lungs, the stomach, the liver, the intestines, and the
kidneys--that is, the hollow organs of the body.

283. The Functions of the Sympathetic System. This system exercises a
superintending influence over the greater part of the internal organs of
the body, controlling to a certain extent the functions of digestion,
nutrition, circulation, and respiration. The influence thus
especially connected with the processes of organic life is generally
different from, or even opposed to, that conveyed to the same organs by
fibers running in the spinal or cranial nerves. These impulses are beyond
the control of the will.

[Illustration: Fig. 121.--The Cervical and Thoracic Portion of the
Sympathetic Nerve and its Main Branches.

A, right pneumogastric;
B, spinal accessory;
C, glosso-pharyngeal;
D, right bronchus;
E, right branch of pulmonary artery;
F, one of the intercostal nerves;
H, great splanchnic nerve;
K, solar plexus;
L, left pneumogastric;
M, stomach branches of right pneumogastric;
N