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330 DESIGN IN NATURE<br />
to move bones which form levers, as in the movements of the arms and legs in locomotion or otherwise ; to move<br />
all parts of the body in the practice of the arts ;<br />
oesophagus, stomach, bladder, rectum, and uterus.<br />
to transmit gases, semi-fluids, solid substances, &c., as in the heart,<br />
Muscles never neutrahse or work against each other. This would altogether defeat the object in view.<br />
All muscular movements are co-ordinated—that is, they are movements to a given end. If the closing or systole<br />
of the heart be sudden, and the opening or diastole slow, it is because the blood has to be hurried forward by a vis<br />
a tergo movement, and time allowed for it to re-enter the ventricles, which, when they open, exercise a vis a fronte<br />
action.<br />
The dehberate co-ordinated movements of the extremities and other parts of the body are inconsistent with<br />
the jerky movements which would be produced by a mechanical forcible dragging out of either the flexor or ex-<br />
tensor muscles during the movements of flexion and extension. It is not conceivable that the dehcate operations<br />
performed by the extremities, hands, feet, and other parts of the body could possibly be effected by muscles (flexors<br />
and extensors, pronators and supinators, abductors and adductors) all playing at cross purposes.<br />
The prevaiHng theory of muscular action fails because it assigns to muscle only one power, namely, the power<br />
of shortening or contracting. As a matter of fact, and as I have shown on several occasions in this work and else-<br />
where, muscle is possessed of a double power, namely, a power by which it elongates or dilates the one instant,<br />
and shortens or contracts the next. This double power admits of the most dehcate co-ordination ; the flexors,<br />
pronators, and abductors shortening or contracting when the extensors, supinators, and adductors elongate, and<br />
vice versd. In this way no power whatever is lost, and the muscles are under the most perfect restraint and control.<br />
There is no violent tugging of muscle against muscle, no muscular warfare ; all is harmony and the outcome of<br />
design. According to this view, there is also provision for perfect rest to the muscles. Muscles are either acting<br />
or at rest. When they act, they act together and at the same time. When they are not acting they are resting.<br />
There is no need for muscles being always on the stretch and in the so-called tonic condition.<br />
An appreciable interval of time (the so-called latent period) elapses between the discharge of motor impulses<br />
and the movements of muscles, but this interval is common to the flexors and extensors, the pronators and supinators,<br />
the abductors and adductors (they form, as explained, co-ordinated groups), so that, when motion occurs in the flexors,<br />
pronators, or abductors, it occurs simultaneously in the extensors, supinators, and adductors, and the converse. If<br />
muscles are suddenly brought into requisition by shpping, sudden loss of balance, &c., before a perfect co-ordina-<br />
tion occurs, the substance of the muscles is not unfrequently ruptured or torn. The several voluntary muscular<br />
movements are associated, co-ordinated movements, and these movements are acquired after much patient and<br />
laborious effort and education. The involuntary muscular movements also admit of being trained. They are at<br />
once fundamental and intuitive, and are stereotyped by unconscious repetition.<br />
The bones and joints, it may be remarked, are not necessary to locomotion. In the Protozoa or unicellular<br />
animals this is effected by an amorphous contractile mass. In the worm, leech, and caterpillar it is effected by<br />
imperfect muscular fibres continuous upon themselves, as in the hollow viscera of Vertebrates. The muscle<br />
becomes interrupted in the Crustaceans by the interposition of an external, and in the Vertebrata by the presence<br />
of an internal, skeleton. When, therefore, the external and internal skeletons make their appearance, it is to<br />
afford the muscular system additional surface and leverage, and to enable it to act with greater precision in<br />
a given direction. The skeleton, since it cannot move of itself, is consequently to be regarded as an adjunct or<br />
auxiliary of the muscular system. As the muscles are accurately moulded to the bones and to each other, either<br />
directly or indirectly (by tendons), and the bones, joints, and muscles move in perfect harmony (the bones being<br />
unyielding or rigid), it follows that the osseous system acts as an artificial break or boundary to the muscular<br />
one—hence the arbitrary division of muscles into extensors and flexors, pronators and supinators, abductors and<br />
adductors, &c. Instead, however, of dividing the muscles into two opposing, disjointed sets, it would be more in-<br />
telligible, and, I believe, more philosophical, to regard them as forming continuous muscular circles or cycles bisected<br />
by bones, the articular surfaces of which enable the cycles to move the bones with absolute precision in any<br />
direction desired. If this plan be adopted, the voluntary system of muscles is readily assimilated to the involuntary,<br />
and both are referred to their original, the continuous elementary fibre.<br />
This view is favoured by analogy, and by the<br />
fact that the muscular system in the higher Vertebrates is in a state of rest (the so-called tonicity of authors), that<br />
is, equally balanced or oscillating between two imaginary fixed points, and ready to act, through its extensors and<br />
flexors, abductors and adductors, pronators and supinators, with surprising rapidity ; the contraction of the ex-<br />
tensors on all occasions involving, but not causing, the relaxation of the flexors, and vice versd. The most highly<br />
organised animal may, in this sense, be regarded as a living mass whose parts (hard, soft, and otherwise) are<br />
accurately adapted to each other, every part reciprocating with scrupulous exactitude, and rendering it difficult<br />
to determine where motion begins and where it terminates,