422 SPECIAL HISTOLOGY. 



thctic going to the peripheral distribution of the spinal nerves, from 

 which again twigs are given off to nerves of the vertebrae ; with respect 

 to which conditions the more detailed observations given in my " Mikr. 

 Anat," II. p. 525, and particularly those of Luschka (" Nerven des 

 Wirbelcanals," p. 10 et seq.) may be consulted. With regard to the 

 question, whence the fibres are derived which join the main trunk of 

 the sympathetic from the spinal nerves, it is certain that that portion of 

 the rami communicantes, which arises from the motor root, and which, 

 according to Luschka, is always a white filament, takes its origin from 

 the cord (or brain) itself, but as regards the other, proceeding from the 

 sensitive root, it may be formed, in part or wholly, from fibres origi- 

 nating in the ganglion. The latter, however, appears to be improbable, 

 for two reasons : 1, because in that case, the existence of conscious 

 sensations from parts supplied by the sympathetic would scarcely be 

 conceivable ; and 2, because the fibres originating in the spinal ganglia 

 are of medium size, whilst, in the rami communicantes, upon the whole, 

 only a few of that kind occur, and these, moreover, must be referred to 

 the motor root. 



We may here offer a few remarks upon the fine fibres of the gan- 

 glionic nerves. It has been long known, that the sympathetic contains 

 a larger proportion of finer nerve-fibres than the cerebro-spinal nerves, 

 but it was not till 1842 that Bidder and Yolkmann labored to show, 

 that these fibres are not only smaller, but also, in other respects, ana- 

 tomically different ; on which account in contradistinction to the thick 

 fibres of the cerebro-spinal nerves, they termed them sympathetic nerve- 

 fibres. In opposition to this, Valentin (" Rep.," 1843, p. 103) and I 

 (" Sympath.," p. 10 et seq.) have endeavored to prove, that the fine 

 fibres in the sympathetic do not constitute a special class, and in this I 

 think we were tolerably successful. The principal reasons are as fol- 

 lows : 1. Fine and thick nerve-fibres do not differ intrinsically in any 

 essential respect except in size, and present the most numerous interme- 

 diate dimensions. 2. Fine nerve-fibres having exactly the same charac- 

 ters as those of the so-termed sympathetic exist in many other situations, 

 as for instance, in Man and the Mammalia, in the posterior roots of 

 the spinal nerves and of the sensitive cerebral nerves, in which situations, 

 as I have already shown, there can be no question whatever as to a 

 derivation of the fibres from the sympathetic, and where we have pre- 

 sented to us, nothing but fine cerebro-spinal fibres ; similar fibres are 

 contained by thousands in the spinal cord and brain, as well as in the 

 two higher nerves of sense. 3. All thick nerve-fibres decrease in size 

 in their ultimate ramifications, owing to divisions, or direct diminution, 

 so that ultimately they acquire the diameter and nature of the fine, 

 and finest kinds of fibres. 4. All thick nerve-fibres in the course of 

 their development are, at one time, exactly in the condition of the so- 



