Encyclopaedia Britannica > Volume 3, Anatomy-Astronomy

ANATOMY.
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and fin¬
gers.
Special These actions are further facilitated and modified by
Anatomy, another class of muscles. The lumbricales, which, situate in
the palm, are attached above to the tendons of the flexor
Minute ■profundus, and inserted sometimes into the extensor ten-
exteivion^ ^ons’ sometimes into the lateral regions of the phalanges,
cx ension. ejther concur with the profundus in bending the first
phalanges, or they may adduct or abduct the fingers, ac¬
cording to the separate or conjunct motion ; and hence are
of the utmost importance in all nice and minute motions of
the fingers. Without the lumbricales, which are peculiar
to man, it would be impossible for the human fingers to
execute those minute and rapid movements which are
necessary in performing on musical instruments; and the
great advantage which one individual possesses over an¬
other in what is denominated execution, consists chiefly in
the perfect use of these little muscles. In playing on the
piano-forte especially, the lumbricales are of the most es¬
sential service; and though the superficial flexor enables
a lady to strike the keys, the former must be employed
in the more minute and delicate motions requisite in the
transition through numerous chords.
In this action the internodii at the same time appear to
be auxiliary; and their connections are calculated to mo¬
dify the action of the flexors.
Opposition Another peculiarity in the human hand consists in the
of thumb four muscles with which the thumb is provided, and the
two connected with the little finger. By means of its
short abductor, short flexor, and adductor, the thumb may
be separated, inflected, and approximated to the hand
quite independently of the fingers, and with the utmost
precision. But from the opponens it derives the remark¬
able property of being accurately and precisely applied to
the tip of any one of the fingers, and thus made to grasp
minute objects, which could not Avithout this be effected.
From this muscle, in short, the human hand derives its
power of appliance to all the arts requiring nice manual
operation. Without the opponens there is no penmanship,
no painting, no drawing, no tracing, no needlework, no
engraving ; in short, none of those operations requiring the
obedience of the hand to the conceptions of the mind and
the guidance of the eye.
The movements of the lower extremities are less dis¬
tinguished for precision and delicacy than those of the
. superior; and though the foot has both lumbricales and inter-
extremi-C osse^ ^le brevity of the phalanges compared with the length
of the metatarsal bones, and the close connection of the
toes, form insurmountable impediments to the rapidity and
nicety of motion which is observed in the inflections of the
fingers. The circumstance, however, which places the foot
at an immeasurable distance behind the hand as an organ
of prehension, is the Avant of the opponens. Void of this,
the human foot is little more than the foot of the quad¬
ruped, constituting chiefly a base of support, and suscep¬
tible of such motions only as are requisite to progression.
It is expedient, therefore, to consider shortly the agents
by which these functions are performed.
Station, or that attitude in which man supports himself
both legs, in the erect position on a horizontal plane, is effected by
the foot being planted firmly on the ground by means of
the gemellus, solceus, tibialis anticus, peronceus longus et
brevis, flexor longus communis digitorum pedis, flexor
hallucis proprius, flexor hallucis brevis, flexor brevis digiti
minimi et digiti medii, the lumbricales, and interossei. At
the same time the leg is fixed to the ground by numerous
muscles,—before by the extensors of the great toe and
toes generally, by the peronceus tertius, partly by the
tibialis anticus ; externally by the peroncei longus et brevis ;
Avithin by the tibialis anticus and posticus; and behind
by the gemellus, solceus, semitendinosus, and long flexors of
VOL. in.
General
move¬
ments of
extremi
ties.
Station on
the toes. The knee is at the same time stretched by the Special
four extensors, aided by the tensor vagince femoris. Anatomy.
The equilibrium of the trunk and pelvis on the heads
of the thigh-bones is maintained by several powerful mus-^11'!10'^*
cles, connecting the former to the latter. Before, for in¬
stance, this action is performed by the sartorius, rectus, the
two psoce, and the iliacus internus ; behind by the biceps,
semitendinosus, and semimembranosus ; without by the glu-
tceus and tensor vagince femoris; and within by the pec-
tinceus, the adductors, and the gracilis. By these muscles
the pelvis is impelled on the axis of the two femora only,
and is prevented from inclining in any other direction. To
maintain the trunk above the pelvis in the same steady
position, numerous other muscles concur. Behind are
the various extensors of the vertebral column and trunk ;
the longissimus dorsi and sacro-lumbalis on each side, the
cervicis descendens, splenius and biventer cervicis ; the trans-
versi cervicis, and spinalis cervicis et dorsi ; the semispinalis,
multifidus, and interspinales on each side. Before are the
sterno-mastoid, the great and small anterior recti, the
longi colli, and anterior scaleni; and on each side are the
trachelo-mastoid, the lateral scaleni, the intertransversi,
and the lateral recti. In this enumeration it is manifest
that the muscles of the posterior surface of the trunk and
spine are at once more numerous and more powerful than
those on the anterior,—an arrangement which is rendered
necessary to counteract the effect of the weight of the
thoracic and abdominal viscera on the anterior side of
the vertebral column, which is thus rendered liable to
anterior incurvation, and which becomes so in old age,
notwithstanding the agents now mentioned.
This circumstance is further illustrated in the number
and size of the muscles by which the head is retained in
the erect position, and prevented from inclining forwards.
These are the cucullares, the splenii capitis, biventres cer¬
vicis, and posterior recti on each side—all powerful, and
several of them large.
Station on both pelvic extremities, therefore, requires
the co-operation of a very considerable number of power¬
ful muscles ; and it is a mistake to imagine, as some authors
appear to do, that a small degree of muscular energy is
requisite for this purpose, and that the skeleton is the
chief means of maintaining the erect position. Without
the skeleton, as points of support, the muscles cannot
act; but without the muscles the bones are passive brute
matter.
In station on one extremity only, a different and cer-Station on
tainly a less degree of muscular action is requisite. Allone lefer-
the external muscles of the fixed member are at first
strongly contracted, to prevent it from gliding inwards, in
which direction the trunk, not supported by the opposite
limb, tends to impel it. Proceeding from below upwards,
we find the lateral peroncei, the vastus externus, and even
the rectus, draw the limb outwards ; Avhile the tensor vagince
femoris, the glutceus medius and minor, carry the pelvis,
and with it the trunk, in the same lateral direction. In
this case the weight of the person is employed in an¬
tagonizing the muscles of the side throAvn into action;
and the person is balanced between these two forces.
Elevation on the tip of the foot is effected chiefly by
the action of the muscles, which extend the phalanges on
the metatarsal bones, viz. the tibialis anticus, extensor hal¬
lucis, extensor longus digitorum, and even the extensor
brevis ; all of which must fix the leg before, and the tarsal
and metatarsal part of the foot on its phalangeal region,
before the latter can be employed to elevate the person.
These extensors, therefore, perform in the tip-toe atti¬
tude the duty which the gastrocnemius and solceus exe¬
cute behind in ordinary station; and the smaller power
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