Part 214

The =visceral branches= comprise aortic, cardiac, pulmonary, and œsophageal branches, and the splanchnic nerves. The =aortic branches= ramify on the thoracic artery, forming around that vessel the =thoracic aortic plexus= (P. aorticus thoracalis). The =cardiac branches= concur with those of the vagus in forming the =cardiac plexus= (P. cardiacus). From this branches go to form the =coronary plexuses= (P. coronarii) along the course of the vessels of like name. The =pulmonary branches= join with corresponding branches of the vagus and filaments from the cardiac plexus in forming the =pulmonary plexus= (P. pulmonalis) at the root of the lung. Branches of the plexus, on which are minute ganglia, ramify with the bronchi in the substance of the lung. The =œsophageal branches= join with those of the vagus in the formation of the =œsophageal plexus= (P. œsophageus).

The =great splanchnic nerve= (N. splanchnicus major) arises by a series of roots derived from the sixth or seventh to the fifteenth or sixteenth thoracic ganglia inclusive. It extends at first along the inner side of the thoracic trunk, then crosses the latter ventrally, passes back between the crus of the diaphragm and the outer border of the psoas minor, and joins the cœliac ganglion. It is small at its origin, but becomes considerably larger than the sympathetic trunk. Near its termination it bears the small =splanchnic ganglion=, from which and from the nerve, filaments go to the aorta, the œsophagus, and the vertebræ.

The =small splanchnic nerve= (N. splanchnicus minor) is formed by roots derived from the last two or three thoracic ganglia. It runs back with the great splanchnic nerve, but ends in the cœliac or in the renal and adrenal plexuses.

This nerve is not always present and is variable in arrangement. The roots communicate by filaments with the great splanchnic.

4. The =abdominal part= of the sympathetic trunk (Pars abdominalis systematis sympathici) lies along the inner border of the psoas minor, above the aorta on the left side and the posterior vena cava on the right (Fig. 524). The trunk is smaller than the thoracic part, and presents usually six small fusiform =lumbar ganglia= (G. lumbalia), which are connected by rami communicantes with the ventral divisions of the lumbar nerves. Visceral branches go to the aortic and hypogastric plexuses, and to the cœliac and mesenteric ganglia.

5. The =pelvic part= of the sympathetic trunk (Pars pelvina systematis sympathici) begins at the last lumbar ganglion and extends along the pelvic surface of the sacrum internal to the emergence of the ventral branches of the sacral nerves (Fig. 451). At the third segment of the sacrum the trunk divides into internal and external branches. The internal branch inclines to the median plane and unites with the opposite branch. At the junction there is often found the small =coccygeal ganglion= (G. impar), which lies on the coccygeal artery at the joint between the first and second coccygeal vertebræ. A filament from the ganglion accompanies the artery. The external branch communicates with the last two sacral nerves and joins the ventral coccygeal nerves. Ganglia occur near each of the first three sacral foramina, and are connected by gray rami communicantes with the adjacent spinal nerves. The visceral branches are distributed through the hypogastric plexus. They supply motor fibers to the longitudinal and inhibitory fibers to the circular muscular coat of the rectum, motor fibers to the bladder and uterus, and the vasodilator fibers (Nn. erigentes) to the penis.

THE ABDOMINAL AND PELVIC PLEXUSES

The chief plexuses which distribute nerves to the viscera and vessels of the abdominal and pelvic cavities are two in number, the solar and the pelvic. From them fibers proceed to form numerous subsidiary plexuses which are named according to the organs which they supply or the vessels which they enlace.

THE SOLAR PLEXUS

The =solar plexus= (Fig. 450) is situated on the dorsal wall of the abdominal cavity in relation to the aorta and the origin of its chief visceral branches. It comprises the cœliaco-mesenteric ganglia and the cœliac and anterior mesenteric plexuses.

The =cœliaco-mesenteric ganglia= are two in number, right and left. They are situated on each side of the aorta, in relation to the origin of the cœliac and anterior mesenteric arteries. The right ganglion is concealed by the posterior vena cava; it is irregularly quadrilateral and is about two inches (4 to 6 cm.) in length. The left ganglion is largely covered by the left adrenal; it is narrower than the right one and is three or four inches (ca. 8 to 10 cm.) long. The two ganglia are united by irregular connecting branches in front of and behind the anterior mesenteric artery. Each receives the splanchnic nerve of its own side and branches from the dorsal œsophageal continuation of the vagus nerves. Branches from the ganglia and the cords which connect them pass back to the small stellate =posterior mesenteric ganglia=, which are situated at the origin of the posterior mesenteric artery.

The =cœliac plexus= (P. cœliacus) consists of a feltwork of nerve-fibers in which are small ganglia. It surrounds the cœliac artery and from it proceed the following unpaired secondary plexuses which accompany the arterial branches:

1. The =gastric plexus= (P. gastricus) enlaces the gastric artery and divides like the artery into two parts, forming the anterior and posterior gastric plexuses. These receive branches of the vagus nerves.

2. The =hepatic plexus= (P. hepaticus) is formed by several nerves of considerable size which accompany the hepatic artery and the portal vein. It receives fibers from the left vagus, ramifies in the liver, and gives off branches which accompany the collateral branches of the hepatic artery and supply the areas in which these vessels are distributed.

3. The =splenic plexus= (P. lienalis) resembles the preceding in its arrangement. In addition to its terminal branches to the spleen, it gives collateral twigs to the pancreas and the left part of the greater curvature of the stomach.

The =anterior mesenteric plexus= (P. mesentericus cranialis) is formed mainly by branches from the posterior part of the cœliaco-mesenteric ganglia; it is continuous with the cœliac plexus in front and the posterior mesenteric behind. It surrounds the anterior mesenteric trunk and its branches, and supplies the viscera to which these vessels are distributed.

The =posterior mesenteric plexus= (P. mesentericus caudalis) accompanies the artery of like name in its distribution.

The secondary plexuses which accompany the branches of the mesenteric arteries give off branches which form two fine peripheral plexuses in the wall of the intestine. One of these, the =myenteric plexus= (P. myentericus) or plexus of Auerbach, lies between the layers of the muscular coat, and is provided with microscopic ganglia. The other is in the submucous tissue, and is therefore termed the =submucous plexus= (P. submucosus) or plexus of Meissner.

The following paired plexuses are derived mainly from branches of the cœliac and aortic plexuses:

1. The =renal plexuses= (P. renales) proceed largely from the cœliaco-mesenteric ganglia, but receive fibers also from the small splanchnic nerves. They enlace the renal arteries and supply the kidneys. Minute renal ganglia occur on the course of the nerves along the renal vessels.

2. The =adrenal plexuses= (P. suprarenales) are formed by a relatively very large number of fine fibers derived in great part directly from the cœliaco-mesenteric ganglia. Numerous minute ganglia occur in their meshes.

3 a. The =spermatic plexuses= (P. spermatid) proceed largely from the aortic and renal plexuses. Each accompanies the corresponding (internal) spermatic artery to the testicle.

3 b. The =utero-ovarian plexuses= (P. ovarici) are the homologues in the female of the preceding. They accompany the utero-ovarian arteries to the ovary and the cornua of the uterus.

The =hypogastric= or =pelvic plexus= (P. hypogastricus) is the pelvic continuation of the aortic and posterior mesenteric plexuses. The chief nerves which form it enter the pelvic cavity ventral to the large vessels, anastomose with each other and with branches from the third and fourth sacral nerves, and ramify on the pelvic viscera. The peripheral plexuses derived therefrom are named according to the organs which they supply; the chief of these are the =hæmorrhoidal=, =vesical=, =uterovaginal=, =prostatic=, =cavernous= (of the penis or clitoris).

THE NERVOUS SYSTEM OF THE OX

The =spinal cord= resembles that of the horse in conformation and structure. In cattle of medium size its length is about 165 to 170 cm. (ca. 65 to 67 inches) and its weight about 240 to 250 grains (ca. 8 ounces).

In a cow 140 cm. in height Dexler found the weight of the cord (including the intradural nerve-roots) to be 260 g. and the length 162 cm. The lengths of the regions were: cervical 41 cm., thoracic 72 cm., lumbar 32 cm., sacral 7 cm.

The =brain= has an average weight of about 500 grams (ca. 16 to 17 ounces). Its differences in general form are correlated with those noted in the consideration of the cranial cavity.