Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/941

Rh SYSTEM.] ANATOMY 883 DESCRIPTIVE ANATOMY OP THE SYMPATHETIC NERVOUS SYSTEM. npatho The Sympathetic Nervous System consists of a pair of nervous gangliated cords, situated one on each side of the spinal tern. column ; of three great gangliated prevertebral plexuses situated in the thoracic and abdominal cavities ; of nume rous smaller ganglia lying more especially in relation with the thoracic and abdominal viscera ; of multitudes of fine distributory nerves. igliated Each Gangliated Cord of the sympathetic extends along 1 and the side of the spine from the base of the skull to the nches. C0 ccyx. In the neck it lies in front of the transverse processes of the vertebras ; in the thorax, in front of the heads of the ribs ; in the abdomen, on the sides of the verte bral bodies; and as it descends in front of the sacrum it approaches its fellow, so that in front of the coccyx the two are united in a single ganglion, the ganglion impar (Fig. 66, c). Each cord consists of a number of ganglia united into a continuous cord by intermediate nerves. As a rule, the ganglia equal in number the vertebraa of the region. Thus, in the sacral region there are five ganglia, in the lumbar five, and in the thorax twelve ; but in the neck there are only three, named superior, middle, and inferior ; of these the superior is very large, and represents without doubt several smaller ganglia. From the superior cervical ganglion the cord is prolonged upwards by an ascending or cranial offshoot through the carotid canal into the cranial cavity, and forms a plexus around the internal carotid artery, both in the carotid canal, named the carotid plexus, and in the inner wall of the cavernous sinus, named the cavernous plexus. Through branches derived either directly or indirectly from these plexuses the sympathetic roots for the ciliary and spheno-palatine ganglia, described in connection with the fifth nerve, are derived. From the gangliated cord and its ascending or cranial prolongation a communicating and a distributory series of branches are derived. By the Communicating branches this portion of the sympathetic is connected with most of the cranial and with the anterior divisions of all the spinal nerves, so as to bring the cerebro-spinal and sympathetic systems into close anatomical and physiological relation with each other. It is important also to observe that each communicating branch contains not only non-medullated nerve fibres from the sympathetic system to the cerebro-spinal nerves, but medullated fibres from the cerebro-spinal to the sympa thetic, so that a double interchange takes place between the two systems. The cranial prolongation of the sympa thetic and the superior cervical ganglion communicate with the 3d and 4th nerves, the Gasserian ganglion of the 5th, the 6th, the portio dura of the 7th, the glosso-pharyngeal and pneumogastric of the 8th, and the 9th_cranial nerves, and with the anterior divisions of the four upper cervical spinal nerves. The middle cervical ganglion communicates with the 5th and 6th cervical nerves, the inferior cervical gan glion with the 7th and 8th cervical nerves, the twelve thoracic ganglia with the series of intercostal nerves, the five lumbar ganglia with the series of lumbar spinal nerves, the sacral and coccygeal ganglia with the sacral nerves and the coccygeal nerve. The Distributory branches of the gangliated cord are as follows : a, Pharyngeal branches from the superior cervical ganglion, which join the pharyngeal branches of the glosso- pharyngeal and pneumogastric nerves, to form the pharyn geal plexus, which supplies the muscles and mucous membrane of the pharynx, b, Articular branches from the upper thoracic and the lumbar ganglia to the articulations between the adjacent vertebrae, c, Pulmonary branches from the 3d or 4th thoracic ganglia, which join the posterior pulmonary plexus, d, Vaso-motor branches or nervi mollcs, which supply the muscular coat of the arteries : those which arise from the cranial prolongation of the superior cervical ganglion supply the internal carotid artery and its branches to the brain and eyeball : those which arise from the superior cervical ganglia itself supply the external carotid artery and its branches; from the branch accompanying the facial artery the submaxilliary ganglion derives its sympathetic root ; from that accompanying the middle meningeal artery the otic ganglion derives its sympathetic root : the vaso-motor nerves which arise from the middle cervical ganglion supply the inferior thyroid artery, and pass to the thyroid gland: the vaso-motor branches of the inferior cervical ganglion supply the vertebral and basilar arteries and their several branches, which pass to the spinal cord and the hinder part? of the encephalon. Vaso-motor nerves also arise from the thoracic ganglia, which pass to the thoracic aorta, from the lumbar ganglia to the abdominal aorta, and from the sacral ganglia to the middle sacral artery; the ganglion impar gives branches to a peculiar vascular struc ture, named the coccygeal body, developed in connection with the end of the middle sacral artery ; a body of similar structure, called intercarotic body, situated in the angle of bifurcation of the common carotid artery, receives branches from the superior cervical ganglion, e, Cardiac branches from the superior, middle, and inferior cervical and the 1st thoracic ganglia, which pass into the thorax to join the pre vertebral cardiac plexus. /, Splanchnic branches as follows : great splanchnic nerve, by the union of branches from the thoracic ganglia, the 3d to the 10th inclusive ; it pierces the eras of the diaphragm, and passes to the prevertebral solar plexus ; small splanchnic nerve, also to the solar plexus from the 10th or llth thoracic ganglia ; smallest splanchnic nerve, from the 12th thoracic ganglion to the renal plexus. g, Hypogastric branches, from the lumbar and sacral ganglia to the prevertebral hypogastric plexus. The Prevertebral Cardiac plexus (PI. XVII. c) is situated Ganglia at the base of the heart, and is divided into a superficial prever- part, which lies in the concavity of the arch of the aorta, and a deep part between the aorta and trachea. It_receives the cardiac branches of the pneumogastric and the cervical ganglia of the sympathetic. It contains collections of nerve cells and a dense plexiform arrangement of nervo fibres. It gives off branches to the heart, which wind around the surface of that organ and penetrate its muscular substance : on these branches minute ganglia are found which regulate its rhythmical movements. Through these branches and the cardiac plexus the heart is brought into connection with both the cerebro-spinal and sympathetic systems of nerves. The sympathetic apparently regulates its contraction, for when this nerve is stimulated the action of the heart is accelerated. The pneumogastric again exer cises an inhibitory or restraining influence on the contrac tions of the organ, for when this nerve is irritated the activity of contraction is diminished, but when divided it is greatly increased. The cardiac plexus also sends offsets to the anterior and posterior pulmonary plexuses for the supply of nerves to the lungs. The Prevertebral Solar or Epigastric plexus is situated at the pit of the stomach around the coeliac axis, a branch of the abdominal aorta. It receives the great and small splanchnic nerves from the thoracic ganglia of the sympa thetic, and some of the terminal branches of the pneumo gastric nerve. It contains large collections of nerve cells, which form the two semilunar ganglia, and a dense plexi form arrangement of nerve fibres. It gives origin, either directly or indirectly, to numerous plexiform branches, which accompany, and are named after, the abdominal aorta and its various branches given off to the walls and viscera of the abdomen proper. In this manner, not only