GENERAL HISTOLOGY OF THE NERVOUS SYSTEM. 117 



connective- tissue corpuscle. Each of these bodies, which he 

 calls an interannular segment, begins and ends at the constric- 

 tion. It contains a single ovoid flattened nucleus, which fills 

 a niche in the myeline, and is surrounded by a broad, thin ex- 

 pansion of protoplasm (the body of the corpuscle). The axis- 

 cylinder has nothing to do with this body that we have de- 

 scribed, except that it pierces it. Instead of stopping short at 

 each constriction, it goes on indefinitely. As we have already 

 seen, the annular constriction and the biconical disk are not 

 always at the same point, which argues strongly for Ranvier's 

 views. The myelinic sheath probably protects the delicate 

 fibre from external injury, but whether it also insulates it, is 

 problematical. In the foetus all nerves are devoid of myeline. 



Fibres of Remak. These are called by some the amyelinic 

 or non-medullated fibres, by others the pale, gray, or gelati- 

 nous fibres. The term Remak' s fibres has come into use re- 

 cently as the distinctive name for certain nerve-fibres abound- 

 ing in the sympathetic, as distinguished from others which 

 also contain no myeline, and are found in the cranial portions 

 of the optic, auditory, and olfactory nerves. Each fibre is 

 marked with oval nuclei at pretty short intervals, and has an 

 indistinct longitudinal striation, probably the evidence of fibrils 

 such as are believed to exist in the axis-cylinder. The nuclei 

 are imbedded in a homogeneous sheath. There being no breaks 

 in the continuity of the fibre, there can be no sheath of Schwann 

 in the sense that has been described. In diameter each fibre va- 

 ries between -fa and T i 7 millimetre. In 1838 Remak first called 

 attention to them, but his views were received with disfavor. 

 More recently, Max Schultze, Frey, Leydig, and Henle have 

 joined in representing them as long, cylindrical, continuous, 

 slightly striated, and dotted with nuclei. 



The fibres of Remak are found in great abundance in all 

 the nerves of the organic system, but they also exist in all the 

 mixed nerves, varying with the kind of nerve and the animal. 

 They are not found in special nerves. The pneumogastric of the 

 cat is well adapted for the study of them, as the myelinic fibres 

 are present in considerable quantity, and make the mechanical 

 separation of the bundle easy. Associated with them, fibres are 

 often seen, that are shown in Fig. 48, c. They are delicate, 

 run a wavy course, and sometimes exhibit curious varicosities 

 (a), (necklace appearance). The nuclei are placed at about the 



