NEURILEMA OF THE WHITE FIBRES. 



547 



completely from one another as the Fig. 216.* 



windings of a silk thread, insulate the 

 coils of wires, which serve as the con- 

 ductors of a galvanic battery. When 

 the bundles of white fibres constituting 

 two or more nerves come together, and 

 appear to anastomose directly or form a plexus, there is there- 

 fore only a separation of the primitive filaments and a recombi- 

 nation of them in a different order as they leave the plexus, so 

 as to render more intimate the connexion existing between differ- 

 ent organs of the body. In this manner the nervous substance 

 of each fibril, is maintained separate in its course, so as to have 

 no functional communication, Fig. 217.f 



except with the part from which 

 it arises, and that to which it is 

 distributed ; and however flexu- 

 ous or involved its direction may 

 be, or with whatever different 

 orders of nerves it may be inci- 

 dentally bound up, its functions 

 are, nevertheless, as directly and 

 singly exercised, as though there 

 existed but one order of fibres 

 in the body. The extremities 

 of the nervous fibres, are not 

 abrupt like the cut ends of a 

 cord. They appear to have their origin in the gray matter in 

 the form of a loop, and to terminate at their distant extremities 

 in loops, which is highly convoluted in the cutaneous papilli 

 and other sensitive parts, as shown in fig. 215. The neurile- 

 matic covering investing the primitive fibres, is very delicate, 

 almost gelatinous or structureless in the brain, so as to render 



* Fig. 216, is a microscopical view, after Raspail, of a transverse sectiou of 

 a branch of a ganglionic nerve, which appears as a single cord. The cut ends 

 of the numerous filaments are here seen, included in the general sheath or 

 neuriiema of the cord. 



■)■ Fig. 217, a similar transverse section of a median nerve, which exhibits 

 several cords, ever}' cord or fasciculus having its own membrane, and all in- 

 cluded in an envelop or neuriiema common to the whole. The cut ends of the 

 fibrils forming each fasciculus are seen. The single dark spot represents a 

 blood-vessel. 



