THE NERVOUS SYSTEM. 



407 



These nerve-cells 



Fig. 155. 



0-004-0-008, the nucleoli 0-0008-0-002 of a line, 

 are situated, in the first place, in larger 

 numbers on the surface of the ganglion, be- 

 tween the neurilemma and the perforating 

 radical fibres ; and secondly, at all events in 

 Man, in the interior, where they occupy the 

 interstices of the plexus formed by the nerve- 

 fibres. The individual cells are retained in 

 their situations by a special tissue, which 

 also separates them from the contiguous cells 

 and from the nerve-fibres. This tissue ap- 

 pears on isolated cells, as if it formed a spe- 

 cial coat to them, and is consequently termed 

 their external sheath, but in fact it repre- 

 sents a system of small septa, connected in a 

 complex manner, and pervading the entire 

 ganglion, receiving the separate cells in its meshes, and only more rarely 

 appearing as a definitely bounded coat on individual cells. This 

 structure is evidently to be referred to connective tissue ; it presents, 

 however, several forms, which have been, in part, already, properly dis- 

 tinguished by Valentin (Mull. "Arch." 1839, p. 143), viz. 1, in the form 

 of a sometimes homogeneous, sometimes more fibrous substance, with 

 scattered, flattened, roundish nuclei of 0-002-0-003 of a 

 line ; and, 2, in that of isolated elongated, triangular or 

 fusiform cells, measuring 0-003-0-005 of a line, with 

 nuclei as above, and which sometimes may be supposed 

 to resemble epithelial cells, although, as is evident from 

 a comparison of their different forms, they rather cor- 

 respond with the developmental cells of connective, or of 

 elastic tissue (Fig. 156). Besides these two forms, the 

 former of which occurs everywhere, and the latter principally in the 

 larger ganglia, certain intermediate types are met with in Man, which 

 consist, as it were, of nucleated "fibres of Remak," as they are termed 

 (vid. infra), or, at all events, in the preparation, break up into such. 



From by far the greatest number of the nerve-cells, in Man and the 

 Mammalia, are given off pale processes, 0-0015-0-0025 of a line, in all 

 respects corresponding to those of the central cells, but furnished with a 

 special sheath, and which, as I discovered in the year 1844 (" Selbst. u. 



FIG. 155. Ganglion-globules (nerve-cells) from the Gasserian ganglion of the Cat, mag- 

 nified 350 diam.: 1, cell with a short, pale process, showing the origin of a fibre, a; 

 sheath of the cell and nerve-tube, containing nuclei; 6, cell-membrane of the nerve-cell; 



2, cell with the origin of a fibre, without sheath ; 6, cell-membrane of the nerve-cell ; 



3, nerve-cell, deprived, in the preparation of it, of its membrane and external sheath. 

 FIQ. 156. Cells from the sheath of the nerve-cells of the spinal ganglia in Man, mag- 

 nified 350 diameters. 



Fig. 156. 



