PHYSIOLOGY. 
arc followed by ttie muscles of respiration, 
and tiie other voluntary muscles close tlie 
enumeration. It is doubted whether the 
arteries or the large venous trunks be irri- 
table. 
The contraction of a muscle consists in a 
shortening of its fibres, which are marked 
by transverse rugas, and feel indurated. But 
although its length is thus diminished, its 
■circumference is proportionally enlarged. 
These circumstances produce an approxi- 
mation of the moveable points to which the 
muscle is attached, and in this way all the 
motions of the body are performed. 
.4n uninterrupted supply of blood, and 
connection with the brain by the nerves, is 
essential to the voluntary action of muscles ; 
ligature of the arteries or nerves destroys 
this power. But these organs still retain 
the faculty of contracting on the application 
of stimuli, even after t’le connection with 
the brain be' cut off, and the animal be in 
other respects dead : this power is the irri- 
tabilitas of Haller, the vis insita, or muscu- 
laris ; which, as that great physiologist and 
his follow'ers contend, is peculiar to the 
muscular fibres exclusively. That this pro- 
perty does not depend on the nerves, is 
clear from the fact of several parts supplied 
with nerves not possessing it; and from its 
remaining after the nerves of a part have 
been divided. 
The nerves may perhaps be regarded as 
the more remote or exciting causes of mus- 
cular motion, of which irritability is the 
proximate or efficient cause. The passions 
of the mind act on the sensorium, which re- 
acts on the nerves of the heart, and thus 
heightens the irritability of that organ, ex- 
citing palpitation and other irregular mo- 
tions. The operations of the will on our 
organs of motion may be explained in the 
Bame way. 
This distinction of the causes of muscular 
motion may be supported by the experi- 
ments in which tlie irritability of the muscles 
has remained after paralysing a part, by tying 
or cutting its nerves ; and by cases of para- 
lysis, in which sensation has remained in a 
limb after its power of motion had ceased, 
or vice versa. 
As it would be a fruitless labour to enu- 
merate and consider all the hypotheses that 
have been framed concerning muscular mo- 
tion, we. shall pass over that part of the 
subject, and refer the reader to the article 
Galvanism for an account of the effects of 
that principle on the muscles. 
The real powfer of muscles is immense. 
In the human body they are generally in. 
serted near the centre of motion, and con* 
sequently with a mechanical disadvantage ; 
so that much of their force is expended in 
overcoming this obstacle. Hence it has 
been calculated, that the deltoid exerts a 
force equal to 2368 pound.s, to surmount a 
resistance of 50 pounds. Tlie force with 
which a muscle contracts is in a direct ratio 
with the number of its fibres; but the degree 
of its contraction, and consequently the ex* 
tent of motions that it can effect on the limb, 
is relative to the length of the fibres. The 
precise limits of contraction in each fibre 
cannot be assigned ; for though the long 
muscles of the extremities are supposed to 
diminish only a third of their length in con- 
traction ; the circular fibres of the stomach, 
which, in the state of extreme dilatation of 
this organ, from circles of nearly a foot in 
diameter, can contract to a ring of one inch 
in circumference. 
Our body contains about four hundred 
and fifty muscles, which when we consider 
their w'onderful and artificial construction 
and collocation, and the united advantages 
of firmness and mobility in the instruments 
of motion to which they are fixed, bestow 
on us two endowments of the highest utility 
and consequence; the greatest agility of 
the whole body and of individual parts, 
combined with a wonderful strength and 
power of enduring continued exertions. 
Both these prerogatives arise partly from 
the perfection in the fabric of the muscle,? 
themselves; which, as well as the perfect 
state of the bones and joints, is most con- 
spicuous in the adult stage of life; and 
partly from exercise andliabit, the inliuence 
of which ill augmenting the extent and 
celerity of muscular motion is most con- 
spicuous in tlie feats of the opera and 
rope dancer, the runner, the boxer, the 
porter, &c. 
Voice and Speech. The voice is a sound 
resulting from the vibrations which the air 
suffers during its passage tlirough the glottis, 
when expelled from the lungs. Speech or 
articulated voice is produced by this sound 
modified by the motions of the tongue, lips, 
and other parts of the mouth. It is oIh 
vious, therefore, that no animals can have a 
voice, unless they possess lungs. 
The larynx is tlie instrument of the voice, 
of which the rima glottidis is the immediate 
organ. Hence, if the trachea be opened 
below, so as to prevent the air from pasting 
througlr, the voice is destroyed ; while, if 
the opening be made above, the speech 
only is destroyed. 
It is universally agreed among physj. 
