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nerve.

THE GREAT SYMPATHETIC.

The phrenic cluded in the group now under consideration, yet, considering its important connection with the motions of respiration, it is proper to describe and illustrate it here.

It arises from the third and fourth cervical nerves, aided by a branch from the fifth, or from the brachial plexus, and from the sympathetic. In its descent it communicates with the lower cervical ganglion, enters the thorax between the subclavian vein and artery, and, passing along the side of the pericardium, descends to the diaphragm, the right phrenic being perpendicular, and the left running obliquely round the apex of the heart. It is distributed, for the most part, to both faces of the diaphragm, superior and inferior. It is the motor nerve of the diaphragm.

ILLUSTRATION OF THE PHRENIC NERVE.

Fig. 174: 1, 1, root of the phrenic nerve, furnished by the fourth cervical; 2, 2, roots from the brachial plexus; anastomosis of this nerve with branch of the subclavian; 4, anastomosis with the inferior cervical ganglion; 5, 5, curve of the hypoglossal, cut, sending a twig to the phrenic nerve; 6, 6, pericardiac branches of the phrenic nerve; 7, 7, branches to the superior face of the diaphragm; 8, 8, branches to the inferior face of the diaphragm; 9, anastomoses of these branches with, 10, the solar plexus; 11, transverse communication of the phrenic nerves.

Position and

OF THE GREAT SYMPATHETIC NERVE.

Under the designations of sympathetic, visceral, trisplanchnic, ganglionic, intercostal, or nerve of organic life, passes a series of structure of the reddish or gray ganglia, interconnected by nervous strands, sympathetic. extending along each side of the vertebral column, from the head to the coccyx, communicating with all other nerves of the body, and distributing branches to the internal viscera, or organs of involuntary function. These ganglia are less numerous than the vertebræ; the chain on each side communicates with its colleague through plexuses, and the ganglion impar is the common uniting point on the coccyx below. By some it is supposed that the ganglion of Ribes, and by others that the pituitary body has the same function in the cranium above.

CONNECTION OF SYMPATHETIC AND SPINAL.

345

What are here spoken of as nervous strands are perhaps more correctly prolongations of the ganglia themselves.

The origin of the sympathetic has been long a subject of dispute, some supposing that it is a special system, of which the ganglia are Origin of the so many independent centres, establishing incidental commu- sympathetic. nications with the cerebro-spinal; others, that its origin is in the internal viscera, and its termination in the cerebro-spinal system, this opinion being supported by the alleged facts that the sympathetic, in its development, appears before the other parts of the nervous system, and simultaneously with the splanchnic organs, and that it has been found in monsters without a brain or spinal cord; others, again, suppose that it originates from the roots of the cerebro-spinal system, and terminates in the interior organs. Regarding it in this light, some have imputed its origin to all the spinal, and fifth and sixth cranial conjointly; others have limited it to the two latter.

tric and sym

The pneumogastric nerve aids it in forming three of its plexuses, the pharyngeal, cardiac, and solar. In certain respects the pneu- Relations of mogastric and sympathetic seem to exhibit a reciprocal de- pneumogasvelopment, in some of the lower animals the former pre- pathetic. dominating over, and supplying the place of the latter; and this replacement, it is said, goes on in the descending series until, in the cephalopodous mollusks, the sympathetic has disappeared, and the pneumogastric takes its place.

Fig. 175.

Fig. 175 illustrates the relation of the sympathetic and spinal nerves: c, c, anterior fissure of the spinal cord; a, anterior root of a dorsal spinal nerve; p, posterior root, with its ganglion; a', anterior branch; p', posterior branch; 8, sympathetic; e, its double junction with the anterior branch of the spinal nerve by a white and a gray filament.

The sympathetic chain therefore establishes connections Connection of with the cerebro-spinal and spinal syssympathetic system. Each spinal tem. nerve is brought into relation with it through two strands, a tubular or white, and a gelatinous or gray. The tubular or white strand may be regarded as actually arising from the spinal cord, and consisting of motor and sensory filaments. It makes its

346

THE GREAT SYMPATHETIC.

way to the ganglion of the sympathetic, passes over and through it, its fibres conjoining themselves with gray ones, which they have gathered in the ganglion. The gray or gelatinous root is to be viewed as having its 'origin in the ganglion of the sympathetic, and sending its fibres chiefly to the ganglion on the posterior root of the spinal nerve, but few of them doubtfully communicating with the anterior root. The fibres which seem to enter the cord are probably for the supply of blood-vessels. Each of these sympathetic ganglia is, therefore, a nervous centre, sending forth strands in three directions: 1st. To join the spinal fibres in their distribution; 2d. To the spinal cord itself, or chiefly to the ganglia on the posterior roots of its nerves; 3d. To the next sympathetic ganglion above. Sympathetic In the various plexuses of the sympathetic, vesicles are found, plexuses. from which gray fibres seem to originate. The branches which supply the viscera constantly form plexuses; the arteries are surrounded with such a net-work. The splanchnic ganglia, with their interconnecting strands, and supplies from the cerebro-spinal, give rise to four great plexuses: the pharyngeal, the cardiac, the solar, and the hypogastric. The first and last of these are in symmetrical pairs; the other two are single, and placed on the median line.

From its construction the sympathetic can not be regarded as an isolated or self-acting system, since all its branches contain Physical effects of sympathetic fibres derived from the cerebro-spinal. In function it must ganglia. therefore be adjuvant to that system, and it must be admitted that the motor and sensory qualities of the included spinal fibres, according as they have been derived from the anterior or posterior columns of the cord, are continued in their association with the sympathetic. Hence, in so far as being a compound nerve, it possesses both those functions, and this conclusion is corroborated by such facts as those of the distribution of the sympathetic both to muscular portions, as to the heart, and also to sensitive ones; by the circumstance that the intestinal canal from the stomach to the end of the colon receives its nervous supply from this source alone. Experiments on the sympathetic ganglia establish a similar conclusion, irritation of the coeliac ganglion, for instance, giving rise to increased peristaltic motions, and pathological observations furnishing like evidence as regards the sensory function. Compared with other nerve trunks, the sympathetic is much less active in these respects, a high irritation of the parts supplied by it often being required to cause pain, and, in like manner, its motor fibres are little under the influence of the will.

The sympathetic transmits sensations so tardily that it has been sup posed that one office of its ganglia is for the purpose of cutting off such impressions; and, in like manner, when motor fibres of the cerebro-spinal system pass through its ganglia, their conducting power appears to

THE GREAT SYMPATHETIC.

347

be impaired. There does not seem to be any decisive proof that any of the fibres of the sympathetic, properly speaking, are motor or sensory, or that its ganglia produce reflex action, the agency which it exerts in these respects on the muscular structure of the heart, blood-vessels, digestive or urinary organs, being due to the associated cerebro-spinal fibres.

In this manner, by its distribution to the arteries, the sympathetic, as a compound nerve, exerts a power over the passage of the blood through them by influencing their contractility, and thereby their diameter. In virtue of this, it therefore affects the rapidity of secretion, and also regulates the rate of nutrition. The entire digestive tract, with its dependencies are thus brought under its influence, the salivary glands, pharynx, œsophagus, stomach, intestine, nasal, bronchial, and pulmonary surfaces, etc.

force.

The view of the function of ganglia presented on preceding pages is strongly supported by the mechanism and phenomena of the Its ganglia are sympathetic nerve. Its ganglia permit the influence passing reservoirs of along the nervous cords to escape therefrom into new channels, and also retain and store up nervous power. They become, therefore, magazines of force, and are hence capable of sustaining rhythmic movements. Even after organs have been exsected, they will still exhibit, under the influence of these ganglia, their accustomed motion, as is the case with the heart, which, in some of the cold-blooded animals, will continue its contractions for many hours after it has been cut out of the body. I therefore regard the sympathetic system as having for one of its main functions the equalization or balancing of the nervous Conclusion force, storing up all transient excesses of it, and furnishing respecting the all transient deficiencies. As in a mechanical contrivance, sympathetic. in which the prime mover works in an irregular way, the fly-wheel harmonizes all such variations, storing up or supplying power as the circumstances may require, so does this complicated apparatus act in the mechanism of innervation. And it is worthy of remark, that some such arrangement would seem to be necessary, since the organs of digestion, to which the sympathetic is so largely directed, are periodically in activity and periodically quiescent.

functions of the

It is to be greatly regretted that the term sympathetic has been applied to this important nerve, since that term, as defining function, has led to the promulgation of theoretical views which have exerted an influence to the disadvantage of the progress of physiology-views which will not bear the test of anatomical criticism, and which are therefore incorrect. It is always much better to give designations in allusion to structure or position than to function, especially where the function is doubtful. For this reason, the title of intercostal is much preferable to that of nerve of organic life, and trisplanchnic better than sympathetic-an

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THE GREAT SYMPATHETIC.

imposing but mysterious epithet, which has been a source of injury to the science, and which it would be well even now to replace by such a term as vincular or moniliform nerve, or some title of equivalent import.

ILLUSTRATION OF THE GREAT SYMPATHETIC.

Fig. 176.

The great sympathetic nerve.

Fig. 176: 1, globe of the eye, dissected so as to show the ciliary nerves; 2, branch of the inferior oblique and the motor root of the ophthalmic ganglion; 3, 3, 3, the three branches of the trifacial, in connection with most of the cranial ganglia, that is, with, 4, ophthalmic ganglion, 5, spheno-palatine, 6, otic, 7, submaxillary, and, 8, sublingual; 9, external motor oculi; 10, facial and its anastomoses with the spheno-palatine and otic ganglia; 11, glosso-pharyngeal; 12, 12, right pneumogastric; 13, left pneumogastric; 14, spinal; 15, hypoglossal; 16, 16, cervical plexus; 17, brachial plexus; 18, 18, intercostal nerves; 19, 19, lumbar plexus ; 20, sacral plexus; 21, superior cervical ganglion, furnishing two carotid branches, forming the carotid plexus around the artery of that name, and from which arise the anastomoses with, 22, nerve of Jacobson, 23, carotid branch of vidian nerve, 24, external motor oculi, 25, ophthalmic ganglion; 26, twig for the pituitary gland; 27, anastomosis of superior cervical ganglion with the first cervical pairs; 28, carotid and pharyngeal branches; 29, pharyngeal and intercarotid plexus; 30, laryngeal

branch, anastomosed with the external laryngeal of the pneumogastric; 31, superior cardiac nerve; 32, strands of junction of the superior cervical ganglion with, 33, middle cervical ganglion: among the internal branches of the latter are, 34, the anastomotic with, 35, the recurrent