OTHER INVOLUNTARY MOTIONS. 7
gature made on the aorta, immediately above its divifion into the
iliacs, the hinder limbs of a dog gradually loft their motion, and
became quite paralytic after two minutes *: from which it may
be thought, that, in the experiments of Langrifti and Schwencke,
the motion of the mufcles continued longer, becaufe they had ftill
fome blood tranfmitted to them by lateral communicating branches,
from arteries which were not tied. But, on the other hand, it
feems more probable, that a ligature on the aorta renders the
mufcles of the legs paralytic, by depriving the inferior part of
the fpinal marrow, and the nerves proceeding from it, of that blond
which contributes to nourifti and keep them in a found ftate [1.].
From what has been faid, we may fairly conclude, that the ar¬
terial blood fent to the mufcles is only neceffary to their motion,,
in fo far as it fupplies the veffels and fibres of the mufcles with
fluids proper for their nourifhment, gives them a fuitable degree
of warmth, and thus preferves them in flieh a ftate as may render
them rnoft fit to be aCted upon by the nervous power. While
therefore the nourifhment and growth of the mufcles are owing to
the motion of the arterial blood through their veffels, their powers
of motion and fenfation proceed from the nerves alone,.
3. The mufcles of living animals are conftantly endeavouring ta
fhorten or contract themfelves. Hence fuch as have antagonifts
are always in a ftate of tenfion ; and the folitary mufcles, fuch as
the fphinCters, and thofe whofe antagonifts are weakened or de-
ftroyed, are always contracted, except when this natural contrao i
tion is overcome by fome fuperior power,.
4. The natural contraction of the mufcles [3.] is owing partly
to all their veffels being diftended with fluids, which feparate and
ftretch their fmalleft fibres.
As a proof of this, the mufcles of animals that are in full health,
and abound with proper fluids, contract themfelves more remark¬
ably towards each extremity when cut acrofs, than the mufcles of
fuch
# Kaau Itapet, facien's, No.. 291.