STRUCTURE OF NERVES. 483 



distributed to any organ. Thus, the smaller nerves of the 

 arm, that are distributed to the different parts, are not to be 

 regarded simply as branches of any one of the five nerves which 

 are appropriated to the upper extremity, but as composed of 

 fibres which are derived from each of them. 



Many of the nerves are enlarged in particular places, so as to 

 form small circumscribed tumors, which are denominated 

 Ganglions. 



These Ganglions are generally of a reddish color. By 

 very dexterous management, they can be shown to consist of 

 a texture of fibres. The larger cords which compose the 

 nerve, seem suddenly to be resolved into the small fibres, of 

 which they consist. These small fibres, after proceeding sepa- 

 rately a greater or lesser distance, according to the size of the 

 ganglion, and changing their relative situation, are again com- 

 bined in cords, which recompose the nerve. 



These fibres appear to be surrounded by a fine cellular 

 substance, which is vascular, moist, and soft. It is asserted 

 that, in fat subjects, an oily substance, resembling fat ; and in 

 hydropic subjects, a serous fluid has been found in this texture. 



Ganglions are often connected with but one nerve, which 

 seems to enter at one extremity and go out at the other. But 

 they frequently receive additional branches from other nerves, 

 and send off additional branches to parts different from those to 

 which their principal nerves are directed. When connected with 

 but one nerve, they have been called simple ganglions : when 

 they receive and give off additional branches, they are denomi- 

 nated compound ganglions. It does not appear that there is any 

 important difference in their structure, in these cases. 



The simple ganglions occur in the nerves of the spinal mar- 

 row — the posterior fasciculus of the nerves having always 

 formed a ganglion before it is joined to the anterior fasciculus. 

 The sympathetic nerve, throughout its whole extent, forms com- 

 pound ganglions. 



The use of this particular structure does not appear to be 

 perfectly known. It seems, however, certain, that the different 

 fibres — (of which the nerves forming ganglions are composed) 

 — are blended together and arranged in a manner different 



