Page 254 - My FlipBook

264 ANATOMY.

(2) tliose conveying the impression received at the peripheral end-organs
to the nerve-centres, known as the sensory nerves and nerves of special
sense, or periphero-central or centripetal nerves ; (3) those which unite
one nerve-centre to another, as the wires passing from one cell to
another in the same battery ; these are known as intercentral nerves.
The Nerve-fibres are of two kinds, medullated and non-meduUated.
The medidlated or dark-border jihren are those which are found in the
cerebro-spinal nerves, with the exception of the olfactory. They vary
Fifi. 116.

Fig. 117.

Ganglion-cell of a Frog (highly
magnified): '/,«, straight fibre;
6, h, coiled fibre c, smaller one A Ganglion-cell within its sheath from the Human
;
joining it. Sympathethic (highly magnified).
fr<
in size troni ^A^tli to ^^^ inch, and are not always of equal size
^^ooO
in the same bundle. In fresh condition the fibre may be described as a
bright, glistening cylinder having a dark double contour, but after death
the outline of the fibre changes and is irregular, the result of decom-
position. The action of water, reagents, or mechanical disturbance pro-
duces the same ap])carance.
By viewing, with a moderate power, a cross-section of a nerve-fibre,
it is .seen to be made up of a varying number of l)undles or fasciculi
of fibres (nerve-fibres Fig. 119). The number of fibres in each fascic-
ulus, and of fasciculi in the nerve, increases or diminishes the size
of the trunk. These fibres and bundles u.sually run parallel to each
other in the .same nerve, except at points Avhere the nerve divides or
bifurcates. The whole is surrounded by connective tissue known as