132 



NERVOUS TISSUE. 



aside their medullary sheath and dark borders, and are prolonged into 

 pale fibres, often minutely dividing, which seem to represent the axis- 

 cylinder deprived of surrounding white substance, and either naked or 

 covered with a prolongation of the primitive sheath. But, apart from 

 these pale continuations of white fibres, there are nerve-fibres Avhich 

 exhibit the non-medullated character throughout their whole length. 

 These are the pale grey fibres first pointed out by Remak, and commonly 

 designated by his name, which are found, with or without associated 

 white fibres, chiefly in the sympathetic but also in other nerves. The 

 branches of the olfactory nerve of man and mammalia consist wholly of 

 these pale fibres. They measure from g oW^h to ^ oW^h of an inch in 

 diameter, appear flattened, translucent, homogeneous, or very faintly 

 granular, and sometimes finely striated longitudinally. At short 

 distances they bear oblong nuclei, which belong to a sheath. In 

 structure these fibres are essentially similar to the axis-cylinder of the 

 medullated fibre, being composed of a bundle of exquisitely fine fibrils 

 with a certain amount of intervening substance. The nucleated sheath 

 corresponds to the primitive sheath of the medullated fibre. 



Pale fibres are also met with (in the sympathetic nerve especially) 

 which appear as fine threads with fusiform enlargements. These enlarge- 

 ments are granular in substance, and possibly of the nature of nuclei, 

 but placed in the continuity of the fibre, and not merely attached to a 

 sheath. 



Nerve-cells. — These, as already mentioned, constitute \he second 

 kind of structural elements proper to the nervous system. They are 

 found in the grey matter of the cerebro-spinal centre and ganglions, 

 constituting a principal part of the last-mentioned bodies, and thence 

 often named (/anglionic corpuscles or ganglion-cells ; they exist also in 

 some of the nerves of special sense at their peripheral expansions, and, 

 here and there, in the course of certain other nerves. The nerve-cells 



Fig. 86. 



Fig. 87. 



Fig. 86.— (jANaLioNio Nerve-Cells, magnified (from Valentin). The cell-processes are 



broken off. 

 n. nucleus. 



Fig. 87. — Nerve-Cells from the Cortical Grey Matter op the Cerebellttii. 

 Magnified 260 diameters (Kolliker). 



may have a spheroidal, oval, or pyriform shape (fig. 86) ; and such for 

 the most part is their form in the ganglia ; but many, and especially 



