410 SPECIAL HISTOLOGY. 



The nerve-tubes or ganglion-fibres thus originating, which frequently 

 arch round or embrace the cells with several circular turns, are at first 

 fine, measuring 0-0015-0*0025 of a line, but (not continuing so as I 

 formerly supposed, when I was acquainted only with their origin), they 

 all very soon increase in size, as may be very readily observed in many 

 fibres, whilst still within the ganglion, up to 0-003 and 0*004, many even 

 to as much as 0-005 and 0-006 of a line; becoming, consequently, medium- 

 sized, and tliick nerve-fihres. The processes of the cells and the nerve-fibres 

 springing from them are also furnished with nucleated sheaths like 

 the cells themselves, the vaginal processes, as they are termed, which 

 they lose, however, at the point where they join the emergent trunk, 

 obtaining instead of it, as a coat, the common neurilemma of the 

 nerves. 



The description I have above given of the conditions observable in 

 the spinal-ganglia in Man and the Mammalia, differs very considerably 

 from what was found by Bidder, Reichert, R. Wagner, and Robin, to be 

 the case in Fishes. The chief difference consists in this, that whilst in 

 the Mammalia, from all we know, the roots of the nerves have no direct 

 connection with the nerve-cells, and merely pass through the ganglion, 

 in Fishes, all the radical fibres are connected with the cells, so that each 

 fibre is interrupted by a bipolar cell, and independent ganglion-fibres are 

 wholly wanting. R. Wagner has thought, that what obtains in the Fish 

 might be applied, unconditionally, to all the Vertebrata, and asserts, that 

 the occurrence of bipolar cells in the course of the posterior radical 

 fibres is in accordance with Bell's doctrine, and a necessary contingent 

 in the mechanism of the sensitive fibres ; and moreover, that in this case 

 the highly important and long-sought distinction between sensitive and 

 motor primitive fibres, has been discovered. In opposition to this I have 

 expressed the opinion, that it is not a necessary postulate, that what is 

 found in the Fish should be applied to Man, and that the interruption of 

 a sensitive fibre by a nerve-cell does not distinguish it from a motor 

 fibre. Although Wagner has very recently characterized this opinion 

 of mine as unphysiological, he will not, at the same time, convince any 

 one that the spinal ganglia of the Mammalia are constructed as he thinks, 

 and I shall therefore wait to see whether further observations will con- 

 firm my observations or not. In order to complete them, I will more- 

 over mention, that direct measurement of the sensitive roots above and 

 below the ganglia, shows a not inconsiderable difference in favor of the 

 latter situation {yid. " Mikroskop. Anat.," II. p. 509), which as diffe- 

 rences in the thickness of the entering and emergent nerve-fibres, and 

 divisions of them within the ganglion do not exist, can only be referred 

 to the fibres which originate in the ganglion and proceed towards the 

 periphery, a view which is also confirmed by direct observation (Fig. 



