ANATOMY. 
excites the aft of fucking; both of which actions are ab- 
folutely neceifary to the maintenance of life, and require 
the nice co-operation of a great number of mufdes prior 
to all experience. Aftions of this kind are called inJlinEl- 
ive ; but, though different from thole of voluntary mo¬ 
tion, they neverthelefs run into one another; lo that wh'at 
was at firft merely inftinftive may afterwards become a 
matter of deliberate choice. The fame mufdes are the. 
inftruments of both ; and they differ from the mufdes 
obeying the internal ftimuli, fuch as the heart, in being 
liable to fatigue, and thereby concurring with the exercile 
of lenfation and of thought, in rendering lleep neceifary. 
There are no nnilcles except thole of refpiration, of which 
the conftant adion is neceifary to life, and which are void 
of confcioufnels in their ordinary exercife, but which are 
yet in fome rneafure under the Controul of the will. The 
principal end anfwered by the power of the will over the 
mufdes of refpiration in man, is to form and regulate 
the voice. But, though inltindive motions are in fome 
cafes convertible into thole which are voluntary, they 
ought by ho means to be confounded together; for, even 
thofe animals which are deftitute of brain and nerves, are 
capable of addons evidently of the inltindive kind. A 
leech, for inllan.ee, being brought into contad with a liv¬ 
ing animal, is impelled by an inllind of its nature to fallen 
upon it, and fuck, its blood. There is fomething very fi- 
milar to this even in vegetables, as in the cafe of tendrils 
and creeping plants being ltimulated by the contact of o- 
tlier bodies to cling round them in a particular diredion. 
It has been demonftrated by Galileo, that in limilar un¬ 
equal bodies, of a cylindrical or prifmatic fliape, fuch as 
the limbs of animals nearly are, the ratio of their efforts 
to break by their own weight is in the quadruplicate ratio 
of their lengths ; but that the reliftance they make to 
the fame force is only the triplicate ratio of their lengths. 
It follows, from this, that, in order to endow the limbs 
of animals with the fame relative force, it is only ne- 
ceffary that the bones fhould poftefs an increafed pro¬ 
portion of thicknefs, in order to give an adequate increafe 
of what may be called the dead ftrength ; but a fimi- 
lar.increafe of living ftrength is neceifary, by a fuitable 
•addition of mufcular power, in order to keep pace with 
the increafed lize of the bones.. Now weoblerve, in fad, 
that in large-fized animals, fuch as the bull and the ele¬ 
phant, the thicknefs both of their bones and mufdes be¬ 
comes greater in proportion to the length of their limbs 
than in the fmaller animals, and they are therefore of a 
lefs elegant form. But nature has not carried this fo far 
as to compenfare for the difadvantage arifing from the in¬ 
creafe of lize ; for the greater animals have not the fame 
proportional ftrength, in relation to their bulk, that the 
fmaller animals have. It has been computed, that a flea 
can draw from l'eventy to eighty times its own weight, 
whereas a horfe cannot with eafe draw more than three 
times his own weight. This difproportion between lize 
and ftrength is very obfervable in different individuals of 
the human fpecies ; for tall men are not mufcular, even in 
the Ample proportion of their ftature.” 
OF THE PARTICULAR MUSCLES. 
Muscles of the Teguments of the Cranium. — The 
fkin that covers the cranium is moved by a Angle broad di- 
gaftric mufcle, and one fmall pair, viz. i. Occipito frontalis, 
arifes flefhy from the tranfverfe protuberant ridge near the 
middle of the os occipitalis laterally, where it joins w ith 
the temporal bone. It is inferted into the orbicularis pal¬ 
pebrarum of each (ide, and into the Ikin of the eye-brows, 
fending down a flefhy flip between them. It pulls the 
Ikin of the head backwards; raifes the eye-brows up¬ 
wards; and draws up the wrinkles of the Ikin of the fore¬ 
head. 2. Corrugator fupercilii, arifes flefhy from the in¬ 
ternal angular procefs of the os frontis, above the joining 
of the os nail, and from thence it runs outwards, and a 
little upwards. It is inferted into the inner and inferior 
flethy part of the occipito-frontalis mufcle, where it joins 
S 6 7 
with the orbicularis palpebrarum. It draws the eye-brow r 
of that fide towards the other, and makes it project over 
the inner canthus of the eye : when both ait, they pull 
down tlie (kin of the forehead, and make it wrinkle, par¬ 
ticularly between the eye-brows. 
Muscles of the Ear. —The mufcles of the ear may 
be divided into three clalfes, viz. the common, proper, 
and internal. The common move the whole ear; the pro¬ 
per only affect the particular parts to which they are con¬ 
nected; and the internal, the fmall bones within the tym¬ 
panum. The common nuifeles are, i. Attollens aurem, ari¬ 
fes thin, broad, and tendinous, from the tendon of the oc¬ 
cipito-frontalis, from which it is almoft infeparable, where 
it covers the aponeurofis of the temporal mulcle. It is in- 
inferted into the upper part of the ear, oppofite to the an¬ 
tihelix, and ferves to draw the ear upwards, and make the 
parts into which it is inferted tenfe. 2. Anterior auris, ari¬ 
fes thin and membranous near the pollerior part of the 
zygoma ; is inlerted into a fmall eminence on the back of 
the helix, oppofite to the concha; and is ufed to draw this 
eminence a little forwards and upwards. 3. Retra/ientes 
auris, arife fometimes by three, but always by two diftinil 
fmall mufcles, from the external and pofterior part of the 
root of the maftoid procefs, immediately above the infer- 
tion of the fterno-cleido-mufcle; are inferted into that 
part of the back of the ear which is oppofite to the fep- 
tum that divides the fcapha and concha; and ferve to 
draw the ear back, and ftretch tlae concha. 
Tlie proper mufcles are, 1. Llelicis major, arifes from the 
upper and acute part of the helix anteriorly; is inlerted 
into its cartilage a little above the tragus ; and ferves to 
deprefs that part, from which it arifes a little downwards 
and forwards. 2. Helicis minor, arifes from the inferior 
and anterior part of the helix ; is inferted into the crus of 
the helix, near the Affure in the cartilage oppofite to the 
concha; and is tiled to contraft the Affure. 3. Tragicus, 
arifes from the middle and outer part of the concha ; is 
inferted into the point of the tragus ; and pulls the point 
of the tragus a little forwards. 4. Antitragicus, arifes from 
the internal part of the cartilage that fupports the anti¬ 
tragus ; and, running upwards, is inferted into the tip of 
the antitragus, as far as the inferior part of the antihelix; 
it turns the tip of the antitragus a little outwards, and de- 
preftes the extremity of the antihelix towards it. 5. Tranf. 
verfus auris, arifes from the prominent part of the concha 
on the dorfum of the ear ; is inlerted oppclite to the outer 
lide of the antihelix ; and draws the parts to which it is con- 
neAled to each other, and llretches the fcapha and concha.. 
The mufcles of the internal ear are three, viz. 1. Lax- 
ator tympani, arifes from the extremity of the fpinous pro¬ 
cefs of the fphenoid bone; then runs backwards, along 
with the nerve called chorda tympani, in a Affure of the os 
temporis that lodges the condyle of the lower jaw. It is 
inferted into the long procefs of the malleus, within the 
tympanum, where it refts upon the edge of the Affure be¬ 
tween the pars fquamofa and petrofa ; and ferves to draw 
the malleus obliquely forwards towards its origin, and 
confequently the membrana tympani. 2. Tcnfor tympani, 
arifes from the cartilaginous extremity of the Euftachian 
tube, near the entry of the artery of the dura mater; from 
thence running backwards near the offeous part of the 
Euftachian tube, and fends off a llender tendon, which 
makes a turn into the tympanum along with the nerve 
called chorda tympani. It is inferted into the pollerior part 
of the handle of the malleus, a little lower than the root 
of its long, procefs; and ferves to pull the malleus and 
membrana tympani inwards towards the pars petrofa, by 
which the membrane is made more concave and tenfe. 
3. Stapedius, arifes from a little cavern in the pars petrofa, 
near the cells of the maftoid procefs; its tendon paffes thro J 
a ltnall hole in the fame cavern, enters the anterior part of 
the tympanum, and is inferted into the pofterior part of the 
head of the ftapes. Its ufe is to draw tire ftapes obliquely 
upwards towards the cavern, by which the pofterior part of 
its bale is moved inwards, and the anterior part outwards. 
