598 



NERVOUS SYSTEM. (NERVE.) 



and therefore have been classed among the 

 nervi untiles, by anatomists. In its peripheral 

 distribution this nerve is prone to attach itself 

 to the coats of bloodvessels, so much so, in 

 fact, as to give it the character of an arterial 

 or venous nerve; for, with a very few exceptions, 

 it is always conveyed to organs along the 

 bloodvessels which are distributed to them. 

 In its distribution it is entirely or almost con- 

 fined to the trunk, and probably has no con- 

 nexion with the extremities; or, if it have, that 

 connexion must be by very few fibres, and 

 those attached exclusively to the larger trunks 

 of bloodvessels. The peripheral ramifications 

 of this nerve are always plexiform, and being 

 distributed on some non-symmetrical parts, 

 the plexuses which are derived from opposite 

 sides of the body meet and anastomose along 

 the mesial plane. The solar plexus, for example, 

 derives filaments from the right and left trunks 

 of the sympathetic, and the plexuses which 

 accompany the superior and inferior mesenteric 

 arteries, are also supplied from each side. Of 

 the precise nature of these plexuses nothing is 

 known: it is obvious, however, that their me- 

 dian anastomoses constitute a very peculiar 

 feature, which strikingly distinguishes the sym- 

 pathetic from the cerebro-spinal nerves, which 

 do not anastomose along the mesial line. If in 

 these anastomoses the looped arrangement exist, 

 it might be conjectured to form a commissural 

 connection between opposite and symmetrical 

 portions of the sympathetic or of the brain or 

 spinal cord. 



To determine the independence of this por- 

 tion of the nervous system on the brain and 

 spinal cord, it would be necessary to shew 

 either that it possessed peculiar fibres distinct in 

 characters from the cerebro-spinal fibres, which 

 originated in the ganglia, and were occasion- 

 ally bound up with cerebro-spinal nerves, or 

 that fibres belonging to the ganglionic nerves, 

 although exhibiting no essential difference from 

 the cerebro-spinal, had their origin from the gan- 

 glia and not from the brain or spinal cord. The 

 present state of the investigations into this sub- 

 ject does not enable us to determine these 

 points; but there can be no doubt that at least 

 a large proportion of the fibres which compose 

 the sympathetic exhibit no essential difference 

 from those of the cerebro-spinal nerves. 



When a portion of a sympathetic nerve is 

 examined under the microscope, it is found to 

 contain an unusually large quantity of white 

 fibrous tissue, the fibres of which are arranged 

 longitudinally. Crossing these are some fine 

 circular fibres (of yellow elastic tissue) which 

 are placed at some distance apart from each 

 other. When the nerve is torn up by needles, 

 numerous small oval cells may be seen among 

 the fibres, their long axes being parallel to the 

 fibres; these cells become much more visible 

 when the fibrous tissue has been acted upon by 

 acetic acid. They are scattered among the other 

 elements of the nerve, and are probably persis- 

 tent nuclei of the same kind as those which 

 exist in muscle and other tissues. Numerous 

 nerve-tubes are also seen entering into the for- 

 mation of these nerves. These tubes appear 

 to correspond in structure exactly with those 



of the cerebro-spinal system; they present the 

 same clear outline, and contain a semifluid 

 pulpy matter, which is acted upon in a similar 

 way by reagents as that in the nerve-tubes of 

 the cerebro*spinal system. They resemble, 

 however, the nerve-tubes of the brain or spinal 

 cord more than those of nerves, for they are 

 much smaller and more delicate than the latter, 

 and more prone to form varicosities. They lie 

 side by side of each other as in other nerves, 

 and do not inosculate. The number of these 

 nerve-tubes seems to vary in different parts of 

 the sympathetic, apparently without regard to 

 the size of the nerve, so that a small nerve may 

 contain several nerve-tubes, while a large one 

 contains but a few. In the abdominal ramifi- 

 cations the nerve-tubes are very numerous, and 

 also in the cardiac nerves, while the sympa- 

 thetic trunk in the neck contains but a few, which 

 are situated quite in the centre of the nerve. 



So far all observers appear to agree in their 

 statements respecting the elementary composi- 

 tion of this nerve, and so far its intimate 

 structure justifies the opinion that in its func- 

 tions it must be intimately connected with the 

 cerebro-spinal nerves. A coarser anatomy had 

 already taught us that this nerve has extensive 

 communications with the cerebro-spinal system, 

 with all the encephalic nerves, excepting those 

 of pure sense, and with all the spinal nerves 

 by their anterior and posterior roots. It is 

 now evident from microscopic observation that 

 the object of these communications must be to 

 enable cerebro-spinal nerve-tubes to pass into 

 the sympathetic system ; and, in short, that 

 these communications may be regarded as so 

 many origins of the sympathetic from the brain 

 and spinal cord. 



It remains to inquire whether there is any 

 good foundation for the doctrine that the sym- 

 pathetic nerve contains distinct and peculiar 

 fibres, (grey fibres of some authors,) which are 

 independent of the brain and spinal cord, and 

 which by anastomosing with cerebral or spinal 

 nerves may confer upon them, to a certain extent, 

 the peculiar endowment which is supposed to 

 characterise the nerves of the former kind. 



Retzius and Muller appear to have been the 

 first to put forward distinctly the opinion that 

 certain cerebro-spinal nerves received parti- 

 cular fibres from the sympathetic, as the latter 

 received filaments from the former. And 

 Miiller* suggested that both the ganglionic and 

 the cerebro-spinal nerves should be looked 

 upon as compound in structure ; " that the 

 ganglionic nerves contain motor, sensitive, and 

 organic fibres, of which the latter kind alone 

 have the power of regulating the vegetative 

 processes, and have a special relation to the 

 ganglia; that the cerebro-spinal nerves are 

 likewise composed of motor, sensitive, and 

 organic fibres, of which those of each kind 

 have their specific destination, and run their 

 course together without uniting with the others; 

 that the ganglionic nerve consequently differs 

 only in having numerous ganglia, and in con- 

 taining a large number of grey fibres, which 

 give it a proportionally greyer colour; while, 



* Muller's Physiology, by Baly, p. 710, 2d edit. 



