176 PALE NEKVE-FIBRES OF THE SYMPATHETIC SYSTEM. 



234. Of the pale nerve-filjrcs of tlie sympatlietic 

 system. — In cases in whicli tlie distance between the 

 nerve centre and the peripheral distribution of the 

 nerves is not very great, the compound fibres are not 

 insulated by a " medullary sheath." In many of the 

 nerve fibres belonging to the so-called sympathetic 

 system there is no " medullaiy sheath," or " white 

 substance of Schw^aun." Where, however, the 

 ganglia or peripheral organs are connected with 

 nerve centres at- a considerable distance off, a number 

 of fibres having this investment are found ; so that 

 amongst the sympathetic nerve fibres, we find dark- 

 bordered nerve-fibres just as commonly as pale fibres 

 occur in the trunks of spinal dark- bordered nerve- 

 fibres (§ 235). In the bladder of the fi-og I have ob- 

 served that where the distance between the ganglion 

 and the peripheral distribution of the nerve fibres is 

 considerable, the fibres have the dark-bordered cha- 

 racter while, on the other hand, if the peiipheral dis- 

 tribution is near the ganglion, the ultimate nerve-fibres 

 are connected with the latter by pale fibres only. 



235. Of fine fibres running with the dark-horderert 

 nerve-fibres. — I have described and figured very fine 

 nerve-fibres running close to the dark-bordered 

 nerve-fibre in the same sheath with it, when there 

 exists a sheath, and in the bundles of dark-bordered 

 nerve-fibres near their distribution, several such fine 

 fibres may be discerned. These fine fibres themselves 

 result from the division of dark-bordered nerve-fibres. 

 Sometimes, a dark-bordered nerve-fibi^e divides into 

 one dark- bordered, and one fine fibre. The fine fibres are 

 in fact the continuation of the dark -bordered fibres, and 

 are very near the point of ultimate distribution. These 

 fi.ne fibres accomjjanying dark-bordered nei've fibres, 

 have not been described or figured by other ob- 

 servers, and are quite undemonstratable in specimens 

 prepared according to the methods usually followed, 

 though they are very distinct indeed in specimens, 



