476 THE NERVOUS SYSTEM. 



different kinds, or that, in the stages of their development, 

 they pass through very different forms. Some of them are 

 small, generally spherical or ovoid, and have a regular 

 uninterrupted outline (fig. 131). These simple nerve-cor- 

 puscles are most numerous in the sympathetic ganglia. 

 Others, which are called caudate or stellate nerve-corpuscles 

 (fig. 132), are larger, and have one, two, or more long 

 processes issuing from them, the cells being called respec- 

 tively unipolar*, bipolar, or multipolar ; which processes often 

 divide and subdivide, and appear tubular, and filled with 

 the same kind of .granular material that is contained within 

 the corpuscle. Of these processes some appear to taper to 

 a point and terminate at a greater or less distance from 

 the corpuscle; some appear to anastomose with similar 

 offsets from other corpuscles ; while others are believed to 

 become continuous with nerve-fibres, the prolongation from 

 the cell by degrees assuming the characters of the nerve- 

 fibre with which it is continuous. 



Functions of Nerve-Fibres. 



The office of the nerves as simple conveyors or con- 

 ductors of nervous impressions is of a two-fold kind. 

 First, they serve to convey to the nervous centres the 

 impressions made upon their peripheral extremities, or 

 parts of their course ; and in this way the mind, through 

 the medium of the brain, may become conscious of external 

 objects. Secondly, they serve to transmit impressions from 

 the brain and other nervous centres to the parts to which 

 the nerves are distributed ; and these impressions seem to 

 be of at least two kinds, those, namely, which excite mus- 

 cular contractions, and those which influence the secretion, 

 nutrition, and other organic functions of a part. 



For this twofold office of the nerves, two distinct sets of 

 nerve-fibres are provided, in both the cerebro-spinal and 

 sympathetic, systems. Those which convey impressions 



