158 STRUCTURE OF THE NERVOUS SYSTEM, BY MAX SCHULTZE. 



where they are invested by a sheath, as simply axis cylinders. 

 It remains undecided whether nerve fibres exist, possessing a 

 medullary sheath and the sheath of Schwann, the axis cylinder 

 of which is formed by a single primitive nerve fibril. 



If the nerve fibres be divided into two groups, according to 

 the presence or absence of the medullary sheath, they may be 

 further subdivided into 



I. Non-medullated fibres. 



1. Primitive fibrils. 



2. Fasciculi of primitive fibrils. 



3. These last, with a sheath of Schwann. 



II. Medullated fibres. 



1. Primitive fibrils with medullary sheath. 



2. Fasciculi of primitive fibrils with medullary sheath. 



3. These last with a sheath of Schwann. 



We see then that the primitive fibril forms the elementary 

 constituent of all nerve fibres. The variations that are ob- 

 served are dependent on the number of the fibrils united 

 together to form one cord, and upon the absence or presence 

 of the medullary sheath and the sheath of Schwann. It is at 

 once obvious how complicated a structure one of the so-called 

 medullated primitive nerve fibres is when it is found to be 

 composed of a bundle of primitive fibrils united by inter- 

 fibrillar material constituting the axis cylinder, and of two 

 investing sheaths. 



The foregoing description differs from that generally received in 

 the acceptance of the primitive fibrils, as the ultimate structural 

 elements of the nerve fibres. I have already elsewhere* shown the 

 probability of the existence of a fibrillar structure in the non-medul- 

 lated fibres of the olfactory and sympathetic nerves, which the greater 

 number of observers have regarded as purely granular rather than 

 fibrous ; and my views have been supported by later observers, as 

 Waldeyer,! Pfliiger,| and others. We must here also take into con- 

 sideration the similarity of the nerve fibres of the greater number of 



* Untersuchungen uber den Bau der Nasenschleimhaut, p. 63. 

 t Zeitschriftftir rationelle Medicin, Band xx., 1863, p. 202. 

 J Die Endigungen der Absonderungsnerven in die Speicheldriisen, 1866, 

 p. 31. 



