THE NERVOUS SYSTEM. 



463 



**£ 





yellow colour. The nuclei measure 001 — - 008'", the nucleoli 

 00008 — 0-002'". These nerve-cells are situated, in the first 

 place, in larger numbers on the sur- 

 face of the ganglion, between 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 appears on iso- 

 lated cells, as if it formed a special coat 

 to them, and is consequently termed 

 their external sheath, but in fact it re- 

 presents a system of small septa, connected in a complex man- 

 ner, 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 distinguished 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 0002 — 

 0*003'"; and, 2. in that of isolated elongated, 

 triangular or fusiform cells, measuring 0*003 

 — 005"', with nuclei as above, and which 

 sometimes may be supposed to resemble epi- 

 thelial cells, although, as is evident from a 

 comparison of their different forms, they rather 

 correspond with the developmental cells of connective, or of 

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



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

 x 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; b, cell-membrane of the nerve- 

 cell : 2, cell with the origin of a fibre, without sheath ; b, cell-membrane of the 

 nerve-cell; 3, nerve-cell, deprived, in the preparation of it, of its membrane and ex- 

 ternal sheath. 



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

 x 350 diam. 



Fig. 156. 



