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PROTOPLASMIC, AMCEBIC, AND OTHER MOVEMENTS 321<br />
antagonists in any way. On the contrary, they form muscular cycles which invest bones with joints—one side or half of the cycle<br />
always contracting or shortening by a centripetal movement, when the other side or half relaxes or elongates by a centrifugal<br />
movement. The muscular cycle formed by the biceps and triceps muscles of the human arm is seen at Fig. 4 ; the arrows (m)<br />
indicating the contracted or shortened sarcous elements of the biceps, and the arrows (re) the relaxed or elongated sarcous<br />
elements of the triceps, as witnessed in flexion of the fore-arm. In extension of the fore-arm, the long axes of the sarcous<br />
elements reverse and change places m becoming n.<br />
The consentaneous centripetal and centrifugal action of the sarcous elements, while well delineated at Fig. 4, is seen to<br />
perfection in the combined movements of the longitudinal and circular muscular fibres of the iris, intestine, ana small arteries<br />
the hollow viscera with sphincters ; and the co-ordinated independent movements of the auricles and ventricles of the mammalian<br />
heart during diastole and systole.<br />
The movements in question are all typified at E and F of Fig. 1 ; E<br />
movement, and F the centripetal, shortening, olosing-up movement (the Author, 1872).<br />
representing the centrifugal, elongating, opening-up<br />
FiG. 2.—A. Fragments of striped elementary fibres, showing transverse cleavage (k, a') of the sarcous<br />
longitudinal cleavage is seen at b. The appearances presented by the separated single tibrillse are shown at<br />
elements. The<br />
c. The sarcous<br />
elements of the fibrillse are, in one case, slightly beaded ; in the other they are perfectly rectangular (after Bowman).<br />
B. Muscular fibres of the pig, magnified 720 diameters. /, Single fibrils showing quadrangular outlines of the component<br />
sarcous elements—their dark central part and bright margin and their lines of junction crossing the light intervals ; d, e, longitudinal<br />
segment of fibres consisting of a number of fibrils still connected together ; /, other smaller collections of fibrils. (From<br />
a preparation by Mr. Leatham, after Dr. Sharpey.)<br />
C and D. Show an elementary muscular fibre of the skate in the uncontracted and contracted states, y, Fibre in the condition<br />
of rest ; the longitudinal and transverse markings and cleavages being well marked. At h one side of the fibre is contracting or<br />
shortening by a wave movement. At i, both sides of the fibre are similarly engaged ; both sides of the fibre being thrown into<br />
wave-like swellings (k, I, in). The remarkable thing is that all the parts of the fibre are capable of producing the wave-like<br />
swellings; these successively taking each other's places. Thus the constrictions between k, I, and m of the letter i become the<br />
swellings n, o of the letter j (after Bowman). The power of the fibre to alternately swell out and expand and to retreat and<br />
draw in, at exactly the same spots, shows that the sarcous elements are endowed with centrifugal and centripetal movements.<br />
As these movements are independent of each other, muscles can alternately shorten and elongate ; the rule being, that when the<br />
one shortens the other elongates, and vice versa. This is the case in voluntary muscles. It is also the case in involuntary muscles<br />
with or without sphincters. When no sphincters are present, the involuntary muscles exert their centripetal power in closing or<br />
partly closing their cavities. When the cavities are to be opened up and expanded they exert their centrifugal power. The<br />
centripetal and centrifugal movements of the voluntary and involuntary muscles are spontaneous and independent, and do not<br />
produce each other (the Author, 1872).<br />
Fig. .3.—Shows the structure of voluntary or striped muscular fibres, and the shapes of the sarcous elements in the relaxed<br />
or elongated, and in the contracted or shortened conditions.<br />
A. Fibrils of extensor muscle of crab's leg in the extended or elongated state.<br />
B. The same separated ; the sarcous elements elongated vertically.<br />
C. Bundles of semi-contracted fibrils from crab's leg—the sarcous elements arranging themselves transversely or horizontally.<br />
D. A further stage of contraction of muscle of crab's leg.<br />
E. Fully contracted or shortened muscle of crab's leg, showing the complete reversal of the long axes of the sarcous elements.<br />
(Compare the sarcous elements of this figure with those of Fig. B.)<br />
P, G. Fasciculi of contracted fibrillse.<br />
In all these figures the longitudinal and transverse cleavages which separate the substance of muscle into sarcous elements<br />
are well marked. (Prom a paper by Rutherford, and as explained by the Author in 1872.);<br />
Flo. 4.—Shows the muscular cycle formed by the biceps or flexor muscle (a) and the triceps or extensor muscle (6) of the<br />
human arm, as seen in the flexion of the fore-arm and hand on the arm (the Author, 1872). At m {vide arrows) the centripetal or<br />
shortening action of the sarcous elements of the biceps in flexion is given, and at n (vide arrows) the centrifugal or elongating<br />
action of the sarcous elements of the triceps in flexion is indicated. The long axes of the sarcous elements, m and n, are at right<br />
angles to each other. In the act of extension of the tore-arm and hand the long axes of the two sets of sarcous elements reverse<br />
the sarcous elements (m) of the biceps have their long axes arranged vertically, and those (n) of the<br />
and change places ; thus<br />
triceps transversely or horizontally. The sarcous elements of the flexor and extensor muscles, as already indicated, always arrange<br />
themselves at right angles—those of the flexors contracting or shortening when those of the extensors relax or elongate, and<br />
vice versa. The flexors do not forcibly drag out the extensors in flexion ; neither do the extensors forcibly drag out the flexors<br />
in extension. This would be a mere waste of power. The flexors and extensors work consentaneously and harmoniously to<br />
produce the acts of flexion and extension respectively. Both are vital acts. There is no jerkiness in either movement, and<br />
elasticity plays quite a subordinate part in muscular action. The present figure illustrates how the bones of the extremities<br />
form levers, and how they are set in motion by muscular action ; the muscles acting in cycles, and, for the most part, spirally,<br />
c, Short and long heads of the biceps or flexor muscle of the arm arising from the coracoid process (i) and upper edge of the glenoid<br />
cavity (and ligament) of the scapula ; d, the insertion of the biceps into the posterior margin of the tuberosity of the radius<br />
e, the three heads of the triceps or extensor muscle of the arm arising from the lower part of the glenoid cavity and inferior<br />
border of the scapula (/) middle or long head ; and from the posterior surface of the humerus—external and internal heads ;<br />
g, the insertion of the triceps into the posterior and upper part of the olecranon of the ulna ; /i, rounded head of the humerus<br />
or arm bone ; i, coracoid process of scapula ; j, j', ulna and radius ; k, elbow joint ; I, bones of hand (the Author, 1872)<br />
PLATE LXXXIV<br />
Plate Ixxxiv. illustrates the views of various authors as regards the shape of the sarcous elements of voluntary<br />
muscle in contraction and relaxation ; hovsr the striation is produced ; how there is a transverse and longitudinal<br />
cleavage of the sarcous elements—these elements being arranged at right angles to each other ; how the transverse<br />
and longitudinal arrangements of the sarcous elements reappear in the smaller blood-vessels, in the intestine, and<br />
in the iris of the eye ; how the transverse and longitudinal sarcous elements work simultaneously and harmoniously,<br />
the transverse sarcous elements shortening when the longitudinal sarcous elements elongate, and vice versd ; how the<br />
VOL. I.<br />
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