162 STRUCTURE OF THE NERVOUS SYSTEM, BY MAX SCHULTZE. 



1. DIVISION OF THE NERVE FIBRES. 



A peculiar feature presented by the nerve fibres in their 

 course is their division. This frequently occurs near their 

 peripheric extremity, but is also to be observed in the nerve 

 centres, and occasionally in the nerve trunks. It may take 

 place in all kinds of nerve fibres, with the exception of the 

 primitive fibrils. Branched and ramified fasciculi of primitive 

 fibrils are composed of the processes of many multipolar gan- 

 glion cells. In the olfactory nerve may be seen the repeated 

 subdivisions, quickly following each other, of non-medullated 

 fibres provided with a sheath of Schwann, with the sheath 

 prolonged upon the branches.* The mode of division, how- 

 ever, that has been most frequently described is that of 

 the medullated fibres, such as is seen, for example, in the 

 nerves distributed to muscle. ( This mode of division 

 is usually dichotomous, and affects all the constituents of 

 the nerve fibre. The division of the fibrillar axis cylinder 

 probably consists only in a gradual process of isolation of the 

 associated primitive fibrils. The medullary sheath is con- 

 tinued at the point of division over the branches, and is finally 

 lost at their extremities. It is very remarkable that at the 

 point of division, in consequence of a sudden diminution in 

 the quantity of the nerve medulla, an attenuation of the nerve 

 fibre occurs, whilst beyond this point, when the division is 

 completed, the medulla is again found in its ordinary propor- 

 tion. The sheath of Schwann divides in precisely the same 

 manner. As the branches after division are much thicker when 

 taken collectively than the trunk from which they proceed, 



* This may be particularly well observed in the thin plates of the nasal 

 fossae of rays and of sharks. Max Schultze, Bau der Nasenschleinhaut, 

 Taf. 4, fig. 8, v. 9. 



t See in particular Reichert and Miiller's Archiv, 1851, p. 29. E. Briicke 

 and Joh. Miiller were the first who observed the divisions of medullated 

 nerve fibres in muscle. See the last mentioned author's Handbuch der 

 Physiologic, fourth edition, Band i., p. 524. Paul Savi was the first who 

 saw the primary divisions of medullated nerve fibres in the electric organs 

 of the Torpedo, in 1844. 



