GENERAL ANATOMY OF TTiE NERVOUS SYSTEM. 3 1 5 



medullary matter is always so arranged that it is never inter- 

 rupted, but forms a continuous whole; while the cineritious is in 

 detached masses, and is found wherever the central extremities 

 of the nerves are implanted, or where there is an increase of 

 medullary fibres. Some anatomists have even supposed that it 

 existed at the peripheral extremities of the nerves, and particu- 

 larly in the rete mucosum of the skin. 



The fibrillae of the medullary tissue are united by a very fine 

 and thin cellular substance, which may be seen by tearing them 

 apart. This cellular substance is more -condensed near the 

 surface of the brain, where it is formed into a highly vascular 

 membrane, the pia mater, and is continued along the nerves as 

 a neurileme, or covering to them. 



The central nervous system is abundantly supplied with 

 blood vessels, but lymphatic trunks have not yet been injected 

 in it. 



The Peripheral Portion of the Nervous System or the Nerves, 

 are formed by parallel anastomosing fasciculi of fibres, percep- 

 tible to simple inspection, which may be reduced into fibrillae, 

 and then again into ^laments as s?nall as the thread of a silk 

 worm. The finest filament is enclosed in its appropriate sheath, 

 so that the latter is a tube filled with nervous matter. The ner- 

 vous matter is soluble in an alkali, and in that way may be re- 

 moved; the canals may then be filled with quicksilver or air, 

 and their existence demonstrated. On the other hand, nitric 

 or muriatic acid dissolves the sheath, but hardens the nervous 

 matter, and renders it more distinct, so that the finest filaments 

 are made obvious.* In either case it is evident that the shape 

 of the nerve is preserved. These filaments are supposed to be 

 precisely the same with the fibres of the brain, excepting that 

 their sheaths keep them more distinct from one another. 



The Sheath of the nerves, or the Neurileme (Neurilemma) 

 forms a general envelope to the nervous fasciculi, as well as a 

 particular one to each fibre, and is continuous, at its central 

 extremity, with the pia mater. Its canals branch off and unite 

 again at intervals, forming a species of reciprocal anastomosis, 



* Reil, de Struct, Nerv. 



