THE NERVOUS SYSTEM. 



453 



large fibres, as they approach both their central and their peripheral 

 <end, lose their medullary sheath, and assume many of the other char- 

 acters of the fine fibres of the sympathetic system, it is not necessary to 

 suppose that there is any material difference in the two kinds of fibres. 



FIG. 312. Gray, pale, or gelatinous nerve-fibres. A. From a branch of the olfactory nerve of 

 the sheep: a, a, two dark-bordered or white fibres from the fifth pair, associated with the pale 

 olfactory fibres. B. From the sympathetic nerve. X 450. (Max Schultze.) 



It is worthy of note, that in the foetus, at an early period of develop- 

 ment, all nerve-fibres are non-medullated. 



Nerve-trunks. Each nerve- trunk is composed of a variable number 

 of different-sized bundles (funiculi) of nerve-fibres which have a special 



FIG. 313. Transverse section of the sciatic nerve of a cat about x 1(R It consists of bundles 

 (Funiculi) 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; AT. 

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



sheath (perineurium or neurilemma). The funiculi are inclosed in a 

 firm fibrous sheath (epineurium)] this sheath also sends in processes of 



