474 THE NERVOUS SYSTEM. 



ment : the nucleus, which is vesicular, contains a nucleolus 

 (fig. 138). Besides varying much in shape, partly in 

 consequence of mutual pressure, they present such other 

 varieties as make it probable either that there are two 

 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. 138). These simple nerve-cor- 

 puscles are most numerous in the sympathetic ganglia. 

 Others, which are called caudate or stellate nerve-corpvscles 

 (fig. 139), are larger, and have one, two, or more long 

 processes issuing from them, the cells being called respec- 

 tively unipolar, bipolar, or midtipolar ; which processes often 

 divide and subdivide, and appear tubular, and filled witli 

 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. Secondly, they serve to transmit 

 impressions from the brain and other nervous centres to 

 the parts to which the nerves are distributed. 



For this two-fold office of the nerves, two distinct sets of 

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

 sympathetic systems. Those which convey impressions 



