EELATIOX OF SYMrATIIETIC TO CEKEBEO-SPINAL XEEVES. 137 



in the first instance to other ganglia of greater or less size (sometimes 

 named praj-vertebial) situated in the thorax, abdomen, and pelvis, and 

 usually collected into groups or coalescing into larger ganglionic masses 

 near the roots of the great arteries of the viscera. 4. Numerous plex- 

 uses of nerves, sent off from these visceral or prre- vertebral ganglia to 

 the viscera, usually creeping along the branches of arteries, and con- 

 taining in various parts little ganglia disseminated among them. Some 

 of these plexuses also receive contributions from spinal or cerebral 

 nerves, by means of branches which immediately proceed to them without 

 previously joining the main series of ganglia. 



Structure of the sympathetic nerve-trunks. — The nervous 

 cords of the sympathetic consist of white fibres, and of pale or grey 

 fibres, mixed with a greater or less amount of filamentous connective 

 tissue, and inclosed in a common external fibro-areolar sheath. The 

 white fibres differ greatly from each other in thickness. A few are of 

 large size, ranging from ttoVo ^^ Woo ^f ^^ ^^^^^ • ^^'^^ most of them 

 are much smaller, measuring from about -^-^^q to -yjo q- of an inch in 

 diameter, and, though having a well-defined sharp outline, for the 

 most part fail to present the distinct double contour seen in the larger 

 and more typical examples of the medullated fibre. The pale, non- 

 medullated fibres, have the characters of Eemak's grey fibres, already 

 described, and often look as if made up of exquisitely fine fibrils ; 

 there are also pale fibres of much less thickness, Avhich, at short dis- 

 tances, are interrupted by, or might be said to swell out into,, fusi- 

 form nuclei. The fibres are in the large trunks collected into bundles or 

 funiculi, the proper sheath of which, or 7ienrilem7na, agrees in structure 

 with that met with in the cerebro-spinal nerves {vide antea, p. 140). 



The more grey-looking branches or bundles of the sympathetic 

 consist of a large number of the pale fibres mixed with a few of the 

 medullated kind ; the whiter cords, on the other hand, contain a pro- 

 portionally large amount of medullated fibres, and fewer of the grey ; 

 and in some parts of the nerve grey fasciculi and white fasciculi, re- 

 spectively constituted as above described, run alongside of each other in 

 the same cords for a considerable space without mixing. This arrange- 

 ment may be seen in some of the branches of communication with the 

 spinal nerves, in the trunk or cord which connects together the principal 

 chain of ganglia, and in the primary branches proceeding from thence 

 to the viscera. In the last-mentioned case the different fasciculi get 

 more mixed as they advance, but generally it is only after the Avhite 

 fasciculi have passed through one or more ganglia that they become 

 thoroughly blended with the grey ; and then, too, the nervous cords 

 receive a large accession of grey fibres (apparently derived from the 

 ganglia), which are mixed up with the rest, and take ofit" more and more 

 from their whiteness. 



Relation of the sympath.etic to tlie cerebro-spinal nerves. — On this impor- 

 tant question two veiy different opinions liave long existed, in one modification or 

 another, amongst anatoinists. 1. According to one, wliich is of old date, but 

 which has been revived and ably advocated by Valentin, the sympathetic set of 

 nerves is a mere dependency, offset, or embranchment of the cerebro-spinal system 

 of nerves, containing no fibres but such as centre in the brain and cord, although 

 it is held that these fibres are modified in then* motor and sensory properties in 

 passing through the ganglia in their way to and from the viscera and involun- 

 tary organs. 2. According to the other view, the sympathetic ner\'e (commonly 



