330 DESIGN IN NATURE 



to move bones which form levers, as in the movements of the arms and legs in locomotion or otherwise ; to move 

 all parts of the body in the practice of the arts ; to transmit gases, semi-fluids, solid substances, &c., as in the heart, 

 oesophagus, stomach, bladder, rectum, and uterus. 



Muscles never neutrahse or work against each other. This would altogether defeat the object in view. 



All muscular movements are co-ordinated — that is, they are movements to a given end. If the closing or systole 

 of the heart be sudden, and the opening or diastole slow, it is because the blood has to be hurried forward by a vis 

 a tergo movement, and time allowed for it to re-enter the ventricles, which, when they open, exercise a vis a fronte 



action. 



The dehberate co-ordinated movements of the extremities and other parts of the body are inconsistent with 

 the jerky movements which would be produced by a mechanical forcible dragging out of either the flexor or ex- 

 tensor muscles during the movements of flexion and extension. It is not conceivable that the dehcate operations 

 performed by the extremities, hands, feet, and other parts of the body could possibly be effected by muscles (flexors 

 and extensors, pronators and supinators, abductors and adductors) all playing at cross purposes. 



The prevaiHng theory of muscular action fails because it assigns to muscle only one power, namely, the power 

 of shortening or contracting. As a matter of fact, and as I have shown on several occasions in this work and else- 

 where, muscle is possessed of a double power, namely, a power by which it elongates or dilates the one instant, 

 and shortens or contracts the next. This double power admits of the most dehcate co-ordination ; the flexors, 

 pronators, and abductors shortening or contracting when the extensors, supinators, and adductors elongate, and 

 vice versd. In this way no power whatever is lost, and the muscles are under the most perfect restraint and control. 

 There is no violent tugging of muscle against muscle, no muscular warfare ; all is harmony and the outcome of 

 design. According to this view, there is also provision for perfect rest to the muscles. Muscles are either acting 

 or at rest. When they act, they act together and at the same time. When they are not acting they are resting. 

 There is no need for muscles being always on the stretch and in the so-called tonic condition. 



An appreciable interval of time (the so-called latent period) elapses between the discharge of motor impulses 

 and the movements of muscles, but this interval is common to the flexors and extensors, the pronators and supinators, 

 the abductors and adductors (they form, as explained, co-ordinated groups), so that, when motion occurs in the flexors, 

 pronators, or abductors, it occurs simultaneously in the extensors, supinators, and adductors, and the converse. If 

 muscles are suddenly brought into requisition by shpping, sudden loss of balance, &c., before a perfect co-ordina- 

 tion occurs, the substance of the muscles is not unfrequently ruptured or torn. The several voluntary muscular 

 movements are associated, co-ordinated movements, and these movements are acquired after much patient and 

 laborious effort and education. The involuntary muscular movements also admit of being trained. They are at 

 once fundamental and intuitive, and are stereotyped by unconscious repetition. 



The bones and joints, it may be remarked, are not necessary to locomotion. In the Protozoa or unicellular 

 animals this is effected by an amorphous contractile mass. In the worm, leech, and caterpillar it is effected by 

 imperfect muscular fibres continuous upon themselves, as in the hollow viscera of Vertebrates. The muscle 

 becomes interrupted in the Crustaceans by the interposition of an external, and in the Vertebrata by the presence 

 of an internal, skeleton. When, therefore, the external and internal skeletons make their appearance, it is to 

 afford the muscular system additional surface and leverage, and to enable it to act with greater precision in 

 a given direction. The skeleton, since it cannot move of itself, is consequently to be regarded as an adjunct or 

 auxiliary of the muscular system. As the muscles are accurately moulded to the bones and to each other, either 

 directly or indirectly (by tendons), and the bones, joints, and muscles move in perfect harmony (the bones being 

 unyielding or rigid), it follows that the osseous system acts as an artificial break or boundary to the muscular 

 one — hence the arbitrary division of muscles into extensors and flexors, pronators and supinators, abductors and 

 adductors, &c. Instead, however, of dividing the muscles into two opposing, disjointed sets, it would be more in- 

 telligible, and, I believe, more philosophical, to regard them as forming continuous muscular circles or cycles bisected 

 by bones, the articular surfaces of which enable the cycles to move the bones with absolute precision in any 

 direction desired. If this plan be adopted, the voluntary system of muscles is readily assimilated to the involuntary, 

 and both are referred to their original, the continuous elementary fibre. This view is favoured by analogy, and by the 

 fact that the muscular system in the higher Vertebrates is in a state of rest (the so-called tonicity of authors), that 

 is, equally balanced or oscillating between two imaginary fixed points, and ready to act, through its extensors and 

 flexors, abductors and adductors, pronators and supinators, with surprising rapidity ; the contraction of the ex- 

 tensors on all occasions involving, but not causing, the relaxation of the flexors, and vice versd. The most highly 

 organised animal may, in this sense, be regarded as a living mass whose parts (hard, soft, and otherwise) are 

 accurately adapted to each other, every part reciprocating with scrupulous exactitude, and rendering it difficult 

 to determine where motion begins and where it terminates, 



