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HANDBOOK OF PHYSIOLOGY. 



olfactory nerve, and are mingled in various proportions in the cerebro- 

 spinal nerves. They differ from the preceding chiefly in their fineness, 

 being only about i to ^ as large in their course within the trunks and 



Fig. 100. Transverse section of the sciatic nerve of a cat about X 100. It consists of bundles 

 CFunzcu/O of nerve-fibres ensheathed in a fibrous supporting capsule, epineurium, A; each bundle 

 has a special sheath ( not sufficiently marked out from the epineurium in the figure) or perineurium 

 B; the nerve-fibres N / are separated from one another by endoneurium ; L, lymph spaces; Ar, 

 artery; V, vein; F, fat. Somewhat diagrammatic. (V. D. Harris.) 



branches of the nerves; in the absence of the double contour; in their 

 contents being apparently uniform ; and in their having, when in bun- 

 dles, a yellowish-gray hue instead of the whiteness of the cerebro-spinal 



Fig. 101. Several fibres of a bundle of medullated nerve-fibres acted upon by silver nitrate to 

 show peculiar behavior of nodes of Ranvier. N, toward this reagent. The silver has penetrated at 

 the nodes, and has stained the axis cylinder, M, for a short distance. S, the white substance. 

 (Klein and Noble Smith.) 



nerves. These peculiarities depend on their not possessing the outer 

 layer of medullary substance; their contents being composed exclusively 

 of the axis-cylinder. Yet, since many nerve-fibres may be found which 

 appear intermediate in character between these two kinds, and since the 



