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, right ventricle;
  O, right auricle;
  P, trunk of pulmonary artery;
  R, aorta; S, cardiac nerves;
  T, recurrent laryngeal nerve;
  U, superior laryngeal nerve;
  V, submaxillary ganglion;
  W, lingual branch of the 5th nerve;
  X, ophthalmic ganglion;
  Y, motor oculi externus.
]

Hence, all these actions of the internal organs just mentioned that are necessary to the maintenance of the animal life, and of the harmony which must exist between them, are controlled by the sympathetic system.  But for this control, the heart would stop beating during sleep, digestion would cease, and breathing would be suspended.  Gentle irritation of these nerves, induced by contact of food in the stomach, causes that organ to begin the churning motion needed for digestion.  Various mental emotions also have a reflex action upon the sympathetic system.  Thus, terror dilates the pupils, fear acts upon the nerves of the small blood-vessels of the face to produce pallor, and the sight of an accident, or even the emotions produced by hearing of one, may excite nausea and vomiting.