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lumbar spinal nerves, and it contains, as well, medullated fibres continued down from the lower part of the thoracic sympathetic trunk, and derived from the visceral branches (white rami communicantes) of the lower thoracic nerves.

This part of the trunk is characterised by great irregularity in the number of the ganglia. They are usually four in number, but there are frequently more (up to eight); and in extreme cases fusion may occur to such an extent that the separation of individual ganglia becomes impossible. 1. Central

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T.12

Gray rami communicantes pass from the gangliated trunk to the anterior rami of the lumbar nerves in an irregular manner. ramus may divide so as to supply branches to two adjacent spinal nerves; or one spinal nerve may be joined by several (two to five) gray rami from the sympathetic E.C. trunk.

FIG. 640.-THE LUMBAR PORTION OF THE SYMPATHETIC

GANGLIATED TRUNK AND LUMBAR PLEXUS. (From a dissection.)

Communicating Branches. White rami communicantes. Only the first two (or three) lumbar spinal nerves send visceral branches (white rami communicantes) to the upper lumbar ganglia or to the sympathetic trunk. These nerves form the lower limit of the thoraciclumbar visceral branches of the spinal nerves. They comprise vasomotor fibres (for the genital organs), and motor fibres for the bladder and uterus.

T.11, T.12, L.1, L.2, L.3, L.4, L.5, Anterior rami of spinal nerves, with white and gray rami communicantes. Sy, Sympathetic trunk; Va, Vagus nerve; G.S, Greater splanchnic nerve, joining coeliac ganglion; S.R.C, Suprarenal gland and plexus; R. Pl, Renal plexus; Ao.Pl, Aortic plexus; S. M, Superior mesenteric plexus; I.M, Inferior mesenteric plexus; Hy. Pl, Hypogastric plexus; Q, Nerves to quadratus lumborum; I.H, Ilio-hypogastric nerve; I.I, Ilio- inguinal nerve; G.C, Genito-femoral nerve; E.C, Lateral cutaneous nerve; A.C, Femoral nerve; Acc. Obt, Accessory obturator nerve; Obt, Obturator nerve; 4, 5, Lumbo-sacral trunk.

The rami course deep to the origin of the psoas major muscle and over the bodies of the vertebræ. Gray rami sometimes pierce the fibres of the psoas muscle.

2. Peripheral Branches of Distribution.-From the lumbar sympathetic trunk numbers of small branches arise irregularly, and supply the abdominal aorta, reinforcing the aortic plexus (derived from the coeliac plexus).

IV. PARS PELVINA SYS-
TEMATIS SYMPATHICI.

The pelvic part of the sympathetic trunk, like the cervical and lower abdominal portions of

The

this system, receives no white rami communicantes from the spinal nerves. visceral branches (pelvic splanchnic) of the third sacral nerve, and usually, also, the second or fourth sacral nerve, enter the plevic plexus without being directly connected with the sympathetic trunk. These nerves, however, are to be regarded as homologous with the white rami communicantes of the thoracico-lumbar nerves (abdominal splanchnic). They convey to the pelvic viscera (1) motor and inhibitory fibres for rectum, uterus, and bladder, (2) vaso-dilator fibres for the genital organs, and (3) secretory fibres for the prostate gland.

This portion of the sympathetic trunk is placed on the pelvic surface of the sacrum, medial to the anterior sacral foramina. It is connected above by a cord with the abdominal portion of the sympathetic, and below it ends in a plexiform union over the coccyx with the trunk of the other side, the two being frequently connected by the ganglion impar or coccygeal ganglion. The number of ganglia is variable; there are commonly four. They are of small size, gradually diminishing from above downwards.

Central communicating branches arise irregularly in the form of gray rami communicantes from the sacral ganglia, which join the anterior rami of the sacral and coccygeal nerves.

Peripheral Branches of Distribution. (1) Visceral branches of small size arise from the upper part of the pelvic sympathetic trunk, and join the pelvic plexus (see below).

(2) Parietal branches, also of small size, ramify over the front of the sacrum, and form, in relation to the middle sacral artery, a plexiform union with branches from the sympathetic trunk of the other side.

PLEXUS SYMPATHICI.

Sympathetic Plexuses. It has already been seen that the peripheral branches of the sympathetic trunk, throughout its length, are characterised by forming or joining plexuses in their neighbourhood.

The cervical sympathetic ganglia and nerves give rise to the carotid and cavernous plexuses; the external carotid, pharyngeal, thyreoid, vertebral, and subclavian plexuses; and they send important branches to the cardiac plexuses (described with the vagus nerve).

The thoracic ganglia send branches to join the pulmonary and œsophageal plexuses (described with the vagus nerve). They form plexuses on the thoracic aorta, and by means of the splanchnic nerves they form the chief source of the coeliac plexus.

THE CELIAC AND PELVIC PLEXUSES.

These great plexuses serve to distribute nerves to the viscera and vessels of the abdominal and pelvic cavities. Taken together they include three plexuses-the coeliac plexus, the hypogastric plexus, and the pelvic plexus. They are constituted by peripheral branches of the lower thoracic, abdominal, and upper pelvic parts of the sympathetic trunk; and they are related to the central nervous system by means of the visceral branches (white rami communicantes) of the lower thoracic and upper lumbar nerves on the one hand, and by the visceral branches of the second and third, or third and fourth sacral nerves, on the other hand. The thoracico-lumbar series join the sympathetic trunk, and reach the coeliac plexus mainly through the splanchnic nerves, and to a lesser extent through the abdominal part of the sympathetic trunk. The sacral series enter the pelvic plexus without connexion with the sympathetic trunk. The hypogastric plexus serves as a connecting link between the coeliac and pelvic plexuses.

PLEXUS CELIACUS.

The cœliac plexus lies on the posterior abdominal wall in relation to the abdominal aorta and behind the stomach. It is composed of three elements: the cœliac plexus surrounding the origin of the coeliac artery, between the crura of the diaphragm; and two coeliac ganglia, each lying on the corresponding crus of the diaphragm, and overlapped by the suprarenal gland, and on the right side by the inferior vena cava. The plexus is continuous with subordinate plexuses, diaphragmatic, suprarenal, renal, superior mesenteric and aortic; and by means of the hypogastric nerves the aortic plexus is continued into the hypogastric plexus, which again forms the chief origin of the pelvic plexuses.

The cœliac ganglia constitute the chief ganglionic centres in the coeliac plexus. They are irregular in form. They are often partially subdivided, and one

detached portion at the lower end is named the aortico-renal ganglion. Other small

scattered masses of cells are present in the coeliac plexus. coeliac ganglion receives the greater splanchnic nerve.

Abdominal sympathetic chain

At the upper end the The aortico-renal ganglion

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Branch from pelvic -sympathetic trunk to pelvic plexus

FIG. 641.-THE SYMPATHETIC IN THE ABDOMEN AND PELVIS.

Nerves to corpus
cavernosum penis

Vesical plexus
Cavernous plexus

Nerves to corpus cavernosum urethræ

at its lower end receives the lesser splanchnic nerve. Branches from the ganglion radiate in all directions-medially to join the coeliac plexus, upwards to form the diaphragmatic plexus, laterally to the suprarenal plexus, downward to the renal, superior mesenteric, and aortic plexuses.

The cœliac plexus forms a considerable plexiform mass surrounding the coeliac artery. It consists of a dense meshwork of fibres with ganglia intermingled, joined by numerous branches from the coeliac ganglion on each side, and by branches from the right vagus nerve. It is continuous below with the superior mesenteric and aortic plexuses. Investing the coeliac artery, it forms subsidiary plexuses which are distributed along the branches of the artery. The left gastric plexus supplies branches to the oesophagus and stomach; the hepatic plexus supplies branches to the liver and gall-bladder, stomach, duodenum, and pancreas; and the splenic plexus sends offsets to the spleen, pancreas, and stomach. Subordinate plexuses are formed on the aorta and its branches by nerves derived from the coeliac ganglia and coeliac plexus.

a. Plexus Phrenicus. The phrenic plexus consists of fibres arising from the coeliac ganglion, and it accompanies the inferior phrenic artery. Besides supplying the diaphragm, it gives branches to the suprarenal plexus, and-on the right side to the inferior vena cava-on the left side to the oesophagus. It communicates on each side with the phrenic nerve. At the junction of the plexus and the phrenic nerve of the right side a ganglion is formed (phrenic ganglion).

b. Plexus Suprarenalis.-The suprarenal plexus is of considerable size. It is mainly derived from branches of the coeliac ganglion, reinforced by nerves from the inferior part of the coeliac plexus which stream laterally on the suprarenal arteries. It is joined by branches from the phrenic plexus above and from the renal plexus below. The nerves enter the substance of the suprarenal gland.

c. Plexus Renalis.—The renal plexus is derived from (1) branches of the cœliac ganglion, and (2) fibres from the aortic plexus, extending laterally along the renal artery to the hilum of the kidney. It receives also the lowest splanchnic nerve, and is connected by numerous branches to the suprarenal plexus.

d. Plexus Mesentericus Superior. The superior mesenteric plexus is inseparable above from the coeliac plexus, and is joined on each side by fibres from the cœliac and aortico-renal ganglia. It is continuous below with the aortic plexus. A separate detached ganglionic mass (superior mesenteric ganglion) is present in the plexus. Accompanying the superior mesenteric artery it forms subordinate plexuses around the branches of the vessel. The plexuses at first surround the intestinal arteries, but near the intestine they form fine plexuses between the layers of the mesentery, from which branches pass to the wall of the gut. This plexus supplies the small intestine, cæcum, vermiform process, ascending and transverse portions of the colon.

e. Plexus Aorticus Abdominalis. The aortic plexus is the continuation downwards of the coeliac plexus around the abdominal aorta. It is continuous above with the coeliac and superior mesenteric plexuses; it is reinforced by the peripheral branches of the lumbar sympathetic trunk; and it is connected with the hypogastric plexus below by the hypogastric nerves. Besides investing and supplying the aorta, the plexus is connected with various subordinate plexuses on the branches of the artery. It contributes to the suprarenal and renal plexuses, and it gives rise to the spermatic or ovarian, and the inferior mesenteric plexuses.

Plexus Spermaticus.-The spermatic plexus invests and accompanies the spermatic artery. It is derived from the aortic plexus, and receives a contribution from the renal plexus. It supplies the spermatic cord and testis.

Plexus Arteriæ Ovarica. The plexus of the ovarian artery in the female arises like the spermatic plexus. It accompanies the ovarian artery to the pelvis, and supplies the ovary, broad ligament, and uterine tube. It forms communications in the broad ligament with the uterine plexus (from the pelvic plexus), and sends fibres to the uterus.

Plexus Mesentericus Inferior.-The inferior mesenteric plexus is a derivative from the aortic plexus, prolonged along the inferior mesenteric artery. It forms subordinate plexuses on the branches of the artery (colic, sigmoid, and superior hæmorrhoidal), and is distributed to the descending colon, iliac colon, pelvic colon, and upper part of the rectum.

PLEXUS PELVINI.

The hypogastric nerves form the continuation of the aortic plexus into the pelvic cavity. They consist of numerous plexiform bundles of nerve-fibres which descend along the front and back of the bifurcation of the aorta and the origin of the common iliac arteries, and over the sacral promontory, where, becoming inextricably mingled, they constitute the hypogastric plexus.

The hypogastric plexus is continued downwards in front of the sacrum on each side of the rectum, and ends in the pelvic plexuses.

The pelvic plexuses are formed by the separation of the hypogastric plexus into two halves at the sides of the rectum. Each is joined by fibres from the upper portion of the pelvic part of the sympathetic trunk, and by the visceral branches (white rami communicantes) from the second and third or third and fourth sacral nerves. Accompanying the hypogastric artery and its branches, each pelvic plexus gives off subordinate plexuses for the pelvic viscera.

a. Plexus Hæmorrhoidalis -The hæmorrhoidal plexus supplies the rectum, and joins the superior hæmorrhoidal plexus from the inferior mesenteric plexus.

b. Plexus Vesicalis.-The vesical plexus accompanies the vesical arteries to the bladder-wall. Besides supplying the muscular wall and mucous membrane of the bladder, it forms subordinate plexuses for the lower part of the ureter, the vesicula seminalis, and the ductus deferens.

c. Plexus Prostaticus.—The prostatic plexus is of considerable size. It is placed on both sides of the gland, and, in addition to supplying its substance and the prostatic urethra, it sends offsets to the neck of the bladder and the vesicula seminalis. It is continued forwards on each side to form the plexus cavernosus penis (cavernous plexus of the penis). Bundles of nerves pierce the layers of the fascia of the urogenital diaphragm, and, after supplying the membranous urethra, give off branches which enter and supply the corpus cavernosum penis. The cavernous nerves communicate with branches of the pudendal nerve and give offsets to the corpus cavernosum urethræ and the penile portion of the urethra.

d. Plexus Uterovaginalis. The uterine plexus passes upwards with the uterine

artery between the layers of the broad ligament, and is distributed to the surfaces and substance of the organ. It communicates between the layers of the broad ligament with the plexus of the ovarian artery.

a

The vaginal plexus is formed mainly by the visceral branches of the sacral nerves entering the pelvic plexus. It supplies the wall and mucous membrane of the vagina and urethra, and provides a cavernous plexus for the clitoris. The uterine and vaginal plexuses of the female correspond to the prostatic plexus of the male.

Spl.

Aa.

Sy.

FIG. 642.-SECTION THROUGH THE SYMPATHETIC TRUNK
OF AN EMBRYO.

Showing the connexion with the ganglion (Sy) of the white
ramus communicans (Spl); (a) a portion of the ramus joining
the ganglion; (3) fibres passing over the trunk, accompanied
by a stream of cells; (7) continuous with those of the gan-
glion; (Ao) Aorta.

THE MORPHOLOGY OF THE
SYMPATHETIC SYSTEM

From a consideration of its structure, functions, and development, there appear to be two separate structures represented in the sympathetic nervous system-the spinal and the sympathetic elements. The structure of the system presents a union of two "sympathetic" cells and fibres. While

distinct elements-fibres of cerebro-spinal origin and the function of the sympathetic trunk and its branches seems to be dependent upon the

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