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NERVOUS SYSTEM — NERVE FIBRILS. 
The Nerve Fibrils are the delicate whitish nerve threads, composed 
nearly exclusively of parallel longitudinal filaments arising directly 
from the ganglia or from the various nerve cords, and whose minute 
ramifications extend to every part of the body; they act as con- 
ductors or conveyors of nerve force or stimuli, to and from the 
various ganglia and the different organs without affecting the inter- 
vening tissues through which they necessarily pass ; they may be 
divided, according to their function, into Afferent or Sensoiy and 
Efferent or Motor nerves. 
The Afferent nerves terminate on the surface of the body or within 
the sensory organs, in the form of suitably modified neuro-epithelial 
cells, and convey tactile or more distinctly specialized acts of per- 
ception to the cerebral or other ganglia, and also connect together the 
Fig. 419. — Afferent nerve fibre, connecting the integumental neuro-epithelial cell with the sensory 
ganglion cell, within which is the nuclear network and the nucleolus, X 600 (after Hernard). 
sensory cells therein. At the surface of the body they form slender 
and fusiform, or externally expanded cells, sometimes bearing tufts of 
sensory hairs, but the ends may also become divided and di.stributed 
within the integument. 
The Efferent nerves unite together the motor cells of the ganglia, 
and convey neivous impulses or impressions from the ganglia to the 
various organs of the body. The efferent nerves may be of a Motor, 
Sympathetic or luhihitory character. The Motor nerves are those 
which terminate within and excite contractions of the muscles of the 
body, or if distributed amongst the glands, excite a more abundant 
aJ w 
Fig. 420. — Efferent nerve fibre, with the motor ganglion cell, from which it arises, and showing 
its connection to a muscle cell, X 6UU (modified after Boa.s). 
flow of their secretions ; the Sympathetic nerves regulate the involun- 
tary and more or less rhythmical motions of the internal organs, while 
the Inhibitory nerves, which chiefly or solely arise from the cerebral 
ganglia, affect the action of all other nerve centres, moderating or 
annulling their influence. The afferent and efferent nerves traverse 
the organs together, but are quite distinct and equally cease to act 
when their connection with the centre is interrupted or destroyed. 
