POST-GANGLIONIC MEDULLATED FIBRES. 651 



The observations of Waller l on the superior cervical ganglion of 

 mammals showed that this ganglion also gives off medullated nerve fibres. 

 He did not himself make this deduction, presumably because he, like 

 many others at the time, considered the question to have been settled 

 by Bidder and Volkmann. He found that section of the cervical 

 sympathetic caused degeneration of the fibres up to the superior cervical 

 ganglion, but not beyond it, and that section of the internal carotid 

 branches of the ganglion caused degeneration in the peripheral 

 branches ; degenerated fibres were followed as far as the ophthalmic 

 nerve. 



These experiments I have repeated, 2 without at the time knowing of 

 Waller's experiments on the internal carotid strands, and with the same 

 results, except that after section of the internal carotid branches a few sound 

 fibres were found in the peripheral end, and a few degenerated fibres in the 

 end attached to the ganglion. 



Kolliker in 1844, in teasing out the fourth thoracic sympathetic ganglion 

 of the cat, found in some cases that one of the processes of the cell could be 

 traced into a medullated fibre. Numerous other similar instances have been 

 recorded in various vertebrates, and in some of the recent observations on 

 sympathetic ganglia by the Golgi and the methylene-blue method, the axons 

 of the cells have been found to become medullated. 



By the degeneration method it can also be shown 3 that the great 

 majority of the small medullated fibres of the grey rami arise from the 

 nerve cells of the corresponding sympathetic ganglion. 



A few of the medullated fibres arise occasionally from an adjoining 

 ganglion, and a few are pre-ganglionic fibres, which are on their way to the 

 aberrant nerve cells of the grey rami. The inferior mesenteric ganglion, and 

 the ganglia of the pelvic plexus, send off very few, and possibly at times no 

 non-medullated fibres. 4 The same appears to be the case with the ganglia on 

 the cranial nerves, 5 with the exception of the ciliary ganglion, but the observa- 

 tions are not very complete. 



So far as investigation has gone, the efferent medullated fibres which 

 arise from nerve cells are all small. 6 



Summing up, then, we find that medullated post-ganglionic fibres 

 are present in mammals, in amphibia, and probably in all vertebrates. 

 They are relatively very much more numerous in amphibia than in 

 mammals; in amphibia, indeed, non-medullated fibres are fewer than 

 medullated, and they vary in number in different mammals. Thus, few 

 medullated fibres are given off by the sympathetic ganglia in the rabbit, 

 but a considerable number in the cat. 



We should naturally expect to find some difference in function 

 between the medullated and the non-medullated post-ganglionic fibres, 

 but there is not at present any evidence of such difference. 



1 " Nouvelle me'thode anatomique, etc.," Bonn, 1852. 



2 Langley, Journ. Physiol., Cambridge and London, 1896, vol. xx. p. 70. 



3 Langley, op. cit. 



4 Langley and Anderson, Journ. Physiol., Cambridge and London, 1894, vol. xvii. 

 p. 177. 



5 On the spheno-palatine ganglion in the dog, cf. Prevost, Arch, de physiol. norm, et 

 path., Paris, 1867, p. 207. 



6 In some cases apparently they are as much as 4 p. in diameter, that is, in the border 

 line between small and medium. 



