526 STRUCTURE OF XERVE-FIBRES. 



optic and auditory nerves. These medullatcd nerve-fibres, without any neurilemma, often show 

 after death, varicose swellings in their course [due to the accumulation of fluid between the 

 medulla of myelin and the axis-cylinder]. Hence they are called varicose fibres. [The varicose 

 appearance is easilv produced by squeezing a small piece of the white matter of the spinal cord 

 between a slide and a cover-glass. Nitrate of silver does not reveal any crosses, and there are 

 no nodes of Rauvier. When acted upon by coagulating reagents, e.g., chromic acid, the 



Fig. 368. 

 1 , Primitive fibrillar ; 2, axis-cylinder ; 3, Remak's fibres ; 4, medullated varicose fibre ; 5, 6, 

 medullated fibre, with Schwann's sheath; c, neurilemma ; t, t, Ranvier's nodes ; b, whito 

 substance of Schwann ; d, cells of the endoneurium ; a, axis-cylinder ; x,' myelin drops ; 

 7, transverse section of nerve-fibres ; 8, nerve-fibre acted on with silver nitrate and show- 

 ing Fromann's lines. I, multipolar nerve-cell from the spinal cord ; z, axial cylinder 

 process; y, protoplasmic processes to the right of it a bipolar cell. II, peripheral 

 ganglionic cell, with a connective-tissue capsule. Ill, ganglionic cell, with o, a spiral, 

 and ?i, straight process ; m, sheath. 



medullary sheath appears laminated, so that on transverse section, when the axis-cylinder is 

 stained, it is surrounded by concentric circles (fig. 869). 



5. Medullated Nerve-Fibres with Schwann's Sheath (fig. 368, 5, 6). These are the most 

 complex nerve-fibres, and are 10 to 22*6 /* \xv\tss to ^nr in ch] broad. They are most 

 numerous in, and in fact they make up the great mass of, the cerebro-spinal nerves, although 

 they are also present in the sympathetic nerves. [When examined in the fresh and living con- 

 dition in situ, they appear refractive and homogeneous (Ranvier, Stirling); but if acted upon 



