408 



SPECIAL HISTOLOGY. 



Fipr.157. 



Abh. des Symp. Nerv.," Zurich, 1844, p. 22), are each of them con- 

 tinued into a dark-bordered nerve tube (Figs. 155, 157). The cells 



observed by me had but one 

 process, the so-termed tmi- 

 polar-cells, and I at first 

 thought that such only ex- 

 isted in the spinal ganglia. 

 It now appears, however, 

 from more recent re- 

 searches, especially from 

 those of Stannius, that they 

 also contain cells with two 

 processes, one of which may again divide ; fresh and more extended in- 

 vestigations therefore are required to show how the matter really stands. 

 At present I think the following should be remarked : 1, in Man and 

 the Mammalia I have certainly established the fact of the existence of 

 unipolar-cells, and think it may also be asserted that they are very nu- 

 merous ; 2, quite lately I have myself, although rarely, noticed cells 

 with two, pale processes, and I am willing to admit the possibility that 

 such cells frequently occur, as it is certain that many processes must be 

 torn off in the comparatively rude methods necessarily employed to 

 isolate the cells ; 3, when Stannius very recently noticed in a human 

 foetus, and in a foetal Calf, together with unipolar and apolar cells, in 

 the latter numerous bipolar cells, it should be inquired whether the lat- 

 ter were not cells which afterwards divide ? — because divisions of the 

 nerve-cells undoubtedly take place (vid. infra), — and in this way become 

 unipolar ; 4, whether the cells give off one or two fibres, one of the 

 latter does not go towards the centre and the other towards the peri- 

 phery, but both proceed in the latter direction ; at all events, in the 

 examination of all small ganglia, only such ganglion-fibres are visible. 

 Stannius, in bipolar cells of this kind from the Calf, also found the two 

 processes closely approximated ; 5, it is difficult to determine whether 

 cells without processes also occur in the spinal ganglia, seeing that the 

 processes are very readily detached, and that cells thus truncated may 

 very easily be regarded as apolar cells. In small ganglia in the Mam- 

 malia a fibre may be traced to each cell, whilst in the smallest spinal 

 ganglia in Man, and in the inconstant ganglia of the posterior roots 

 (vid. seq.), cells are not unfrequently met with, to which no fibre is at- 

 tached, and, consequently, I would, at present, merely state that, in any 

 case, fibres arise from the majority of the cells. In order to examine 

 these conditions, either the larger ganglia in Man are selected, which 



Fig. 157. — Twigs of the coccygeal nerve within tlie dura mater, with an adherent, pedun- 

 culated nerve-cell in its nucleated sheath, from wliich the derivation of a fibre is very 

 distinctly seen ; magnified 350 diameters. From Man. 



