THE NERVOUS SYSTEM. 153 



no certainty that in structure the branches of cerebral or spinal nerves 

 differ always from those of the sympathetic system, it is impossible in 

 the present state of our knowledge to be sure of" the source of fibres 

 which from their structure might lead the observer to believe that they 

 arose from the brain or spinal cord on the one hand, or from the sym- 

 pathetic ganglia on the other. In other words, although the large white 

 medullated fibres are especially characteristic of cerebro-spinal nerves, and 

 the pale or non-medullated fibres of a sympathetic nerve, in which they 

 largely preponderate, there is no certainty to be obtained in a doubtful 

 case, of whether the nerve-fibre is derived from one or the other, from 

 mere examination of its structure. It may be derived from either source. 



Functions. It may be stated generally that the sympathetic nerve- 

 fibres are simple conductors of impressions,, as are those of the Cerebro- 

 spinal system; and that the ganglionic centres have (each in its appropri- 

 ate sphere) the like powers both of conducting, transferring, reflecting, 

 and possibly of augmenting or of inhibiting impressions made on them. 



The power possessed by the sympathetic ganglia of conducting impres- 

 sions is sufficiently proved in disease, as when any of the viscera, usually 

 unfelt, give rise to sensations of pain, or when a part not commonly sub- 

 ject to mental influence is excited or retarded in its actions by the vari- 

 ous conditions of the mind; for in all these cases impressions must be 

 conducted to and fro through the whole distance between the part and 

 the spinal cord and brain. So, also, in experiments, now more than 



FIG. 348. Diagrammatic view of the Sympathetic cord of the right side, showing its connections 

 with the principal cerebro-spinal nerves and the main prseaortic plexuses. 1-4. (From Quain's 

 Anatomy.) 



Cerebro-spinal nerves. VI, a portion of the sixth cranial as it passes through the cavernous 

 sinus, receiving two twigs from the carotid plexus of the sympathetic nerve; O, ophthalmic ganglion 

 connected by a twig with the carotid plexus; M, connection of the spheric-palatine ganglion by the 

 Vidian nerve with the carotid plexus; C, cervical 



j cervical plexus ; Br, brachial plexus ; D 6, sixth intercostal 



nerve; D 12, twelfth; L 3, third lumbar nerve; S 1, first sacral nerve; S 3, third; S 5, fifth; Cr, an- 

 terior crural nerve; Cr', great sciatic; pn, pneumogastric nerve in the lower part of the neck; r, re- 

 current nerve winding round the subclavian artery. 



Sympathetic Cord.c, superior cervical ganglion; c', second or middle; c", inferior: from each of 

 these ganglia cardiac nerves (all deep on this side) are seen descending to the cardiac plexus; d 1, 



E laced immediately below the first dorsal sympathetic ganglion; d 6, is opposite the sixth; 1 1, first 

 imbar ganglion; c g, the terminal or coccygeal ganglion. 



P>-ceaortic and Visceral Plexuses. p p, pharyngeal, and, lower down, laryngeal plexus; pi, pos- 

 terior pulmonary plexus spreading from the vagus on the back of the right bronchus; o a, on the 

 aorta, the cardiac plexus, toward which, in addition to the cardiac nerves from the three cervical 



ninth dorsal ganglia; +, small splanchnic from the ninth and tenth; + +, smallest or third splanch- 

 nic from the eleventh: the first and second of these are shown joining the solar plexus, s o; the third 

 descending to the renal plexus, r e; connecting branches between the solar plexus and the vagi are 

 also represented; pri, above the place where the right vagus passes to the lower or posterior surf ace 

 of the stomach; pn", the left distributed on the anterior or upper surface of the cardiac portion of 

 the organ: from the solar plexus large branches are seen surrounding the arteries of the cceliac axis. 

 and descending to m s, the superior mesenteric plexus; opposite to this is an indication of the supra- 

 renal plexus; below r e (the renal plexus), the spermatic plexus is also indicated; a o, on the 

 front of the aorta, marks the aortic plexus, formed by nerves descending from the solar and supe- 

 rior mesenteric ' 

 rounding the cor 



connected above with the aortic plexus, receiving nen 

 below into the right and left pelvic or inferior hypogastric plexuses; pi, the right pelvic plexus: 

 from this the nerves descending are joined by those from the plexus on the superior hemorrhoidal 

 vessels, mi', by sympathetic nerves from the sacral ganglia, and by numerous visceral nerves from 

 the third and fourth sacral spinal nerves, and there are thus formed the rectal, vesical, and other 

 plexuses, which ramify upon the viscera from behind forward and from below upward, as toward 

 ir, and v, the rectum and bladder. 



