courtship, expand their throat pouches or frills, and erect their
dorsal crests.[416] But Dr. Gunther does not believe that they can
erect their separate spines or scales.
We thus see how generally throughout the two higher vertebrate classes,
and with some reptiles, the dermal appendages are erected under the
influence of anger and fear. The movement is effected, as we know from
Kolliker s interesting discovery, by the contraction of minute,
unstriped, involuntary muscles,[417] often called _arrectores pili_,
which are attached to the capsules of the separate hairs, feathers, &c.
By the contraction of these muscles the hairs can be instantly erected,
as we see in a dog, being at the same time drawn a little out of their
sockets; they are afterwards quickly depressed. The vast number of
these minute muscles over the whole body of a hairy quadruped is
astonishing. The erection of the hair is, however, aided in some cases,
as with that on the head of a man, by the striped and voluntary muscles
of the underlying _panniculus carnosus_. It is by the action of these
latter muscles, that the hedgehog erects its spines. It appears, also,
from the researches of Leydig[418] and others, that striped fibres
extend from the panniculus to some of the larger hairs, such as the
vibrissae of certain quadrupeds. The _arrectores pili_ contract not
only under the above emotions, but from the application of cold to the
surface. I remember that my mules and dogs, brought from a lower and
warmer country, after spending a night on the bleak Cordillera, had the
hair all over their bodies as erect as under the greatest terror. We
see the same action in our own _goose-skin_ during the chill before a
fever-fit. Mr. Lister has also found,[419] that tickling a neighbouring
part of the skin causes the erection and protrusion of the hairs.
From these facts it is manifest that the erection of the dermal
appendages is a reflex action, independent of the will; and this action
must be looked at, when, occurring under the influence of anger or
fear, not as a power acquired for the sake of some advantage, but as an
incidental result, at least to a large extent, of the sensorium being
affected. The result, in as far as it is incidental, may be compared
with the profuse sweating from an agony of pain or terror.
Nevertheless, it is remarkable how slight an excitement often suffices
to cause the hair to become erect; as when two dogs pretend to fight
together in play. We have, also, seen in a large number of animals,
belonging to widely distinct classes, that the erection of the hair or
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