PROTOPLASMIC, AMCEBIC, AND OTHER MOVEMENTS 321 



antagonists in any way. On the contrary, they form muscular cycles which invest bones with joints — one side or half of the cycle 

 always contracting or shortening by a centripetal movement, when the other side or half relaxes or elongates by a centrifugal 

 movement. The muscular cycle formed by the biceps and triceps muscles of the human arm is seen at Fig. 4 ; the arrows (m) 

 indicating the contracted or shortened sarcous elements of the biceps, and the arrows (re) the relaxed or elongated sarcous 

 elements of the triceps, as witnessed in flexion of the fore-arm. In extension of the fore-arm, the long axes of the sarcous 

 elements reverse and change places — m becoming n. 



The consentaneous centripetal and centrifugal action of the sarcous elements, while well delineated at Fig. 4, is seen to 

 perfection in the combined movements of the longitudinal and circular muscular fibres of the iris, intestine, ana small arteries ; 

 the hollow viscera with sphincters ; and the co-ordinated independent movements of the auricles and ventricles of the mammalian 

 heart during diastole and systole. 



The movements in question are all typified at E and F of Fig. 1 ; E representing the centrifugal, elongating, opening-up 

 movement, and F the centripetal, shortening, olosing-up movement (the Author, 1872). 



FiG. 2. — A. Fragments of striped elementary fibres, showing transverse cleavage (k, a') of the sarcous elements. The 

 longitudinal cleavage is seen at b. The appearances presented by the separated single tibrillse are shown at c. The sarcous 

 elements of the fibrillse are, in one case, slightly beaded ; in the other they are perfectly rectangular (after Bowman). 



B. Muscular fibres of the pig, magnified 720 diameters. /, Single fibrils showing quadrangular outlines of the component 

 sarcous elements — their dark central part and bright margin and their lines of junction crossing the light intervals ; d, e, longi- 

 tudinal segment of fibres consisting of a number of fibrils still connected together ; /, other smaller collections of fibrils. (From 

 a preparation by Mr. Leatham, after Dr. Sharpey.) 



C and D. Show an elementary muscular fibre of the skate in the uncontracted and contracted states, y, Fibre in the condition 

 of rest ; the longitudinal and transverse markings and cleavages being well marked. At h one side of the fibre is contracting or 

 shortening by a wave movement. At i, both sides of the fibre are similarly engaged ; both sides of the fibre being thrown into 

 wave-like swellings (k, I, in). The remarkable thing is that all the parts of the fibre are capable of producing the wave-like 

 swellings; these successively taking each other's places. Thus the constrictions between k, I, and m of the letter i become the 

 swellings n, o of the letter j (after Bowman). The power of the fibre to alternately swell out and expand and to retreat and 

 draw in, at exactly the same spots, shows that the sarcous elements are endowed with centrifugal and centripetal movements. 

 As these movements are independent of each other, muscles can alternately shorten and elongate ; the rule being, that when the 

 one shortens the other elongates, and vice versa. This is the case in voluntary muscles. It is also the case in involuntary muscles 

 with or without sphincters. When no sphincters are present, the involuntary muscles exert their centripetal power in closing or 

 partly closing their cavities. When the cavities are to be opened up and expanded they exert their centrifugal power. The 

 centripetal and centrifugal movements of the voluntary and involuntary muscles are spontaneous and independent, and do not 

 produce each other (the Author, 1872). 



Fig. .3. — Shows the structure of voluntary or striped muscular fibres, and the shapes of the sarcous elements in the relaxed 

 or elongated, and in the contracted or shortened conditions. 



A. Fibrils of extensor muscle of crab's leg in the extended or elongated state. 



B. The same separated ; the sarcous elements elongated vertically. 



C. Bundles of semi-contracted fibrils from crab's leg — the sarcous elements arranging themselves transversely or horizontally. 



D. A further stage of contraction of muscle of crab's leg. 



E. Fully contracted or shortened muscle of crab's leg, showing the complete reversal of the long axes of the sarcous elements. 

 (Compare the sarcous elements of this figure with those of Fig. B.) 



P, G. Fasciculi of contracted fibrillse. 



In all these figures the longitudinal and transverse cleavages which separate the substance of muscle into sarcous elements 

 are well marked. (Prom a paper by Rutherford, and as explained by the Author in 1872.); 



Flo. 4. — Shows the muscular cycle formed by the biceps or flexor muscle (a) and the triceps or extensor muscle (6) of the 

 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 

 shortening action of the sarcous elements of the biceps in flexion is given, and at n (vide arrows) the centrifugal or elongating 

 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 

 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 

 and change places ; thus the sarcous elements (m) of the biceps have their long axes arranged vertically, and those (n) of the 

 triceps transversely or horizontally. The sarcous elements of the flexor and extensor muscles, as already indicated, always arrange 

 themselves at right angles — those of the flexors contracting or shortening when those of the extensors relax or elongate, and 

 vice versa. The flexors do not forcibly drag out the extensors in flexion ; neither do the extensors forcibly drag out the flexors 

 in extension. This would be a mere waste of power. The flexors and extensors work consentaneously and harmoniously to 

 produce the acts of flexion and extension respectively. Both are vital acts. There is no jerkiness in either movement, and 

 elasticity plays quite a subordinate part in muscular action. The present figure illustrates how the bones of the extremities 

 form levers, and how they are set in motion by muscular action ; the muscles acting in cycles, and, for the most part, spirally, 

 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 

 cavity (and ligament) of the scapula ; d, the insertion of the biceps into the posterior margin of the tuberosity of the radius ; 

 e, the three heads of the triceps or extensor muscle of the arm arising from the lower part of the glenoid cavity and inferior 



border of the scapula (/) middle or long head ; and from the posterior surface of the humerus — external and internal heads ; 



g, the insertion of the triceps into the posterior and upper part of the olecranon of the ulna ; /i, rounded head of the humerus 

 or arm bone ; i, coracoid process of scapula ; j, j', ulna and radius ; k, elbow joint ; I, bones of hand (the Author, 1872) . 



PLATE LXXXIV 



Plate Ixxxiv. illustrates the views of various authors as regards the shape of the sarcous elements of voluntary 

 muscle in contraction and relaxation ; hovsr the striation is produced ; how there is a transverse and longitudinal 

 cleavage of the sarcous elements— these elements being arranged at right angles to each other ; how the transverse 

 and longitudinal arrangements of the sarcous elements reappear in the smaller blood-vessels, in the intestine, and 

 in the iris of the eye ; how the transverse and longitudinal sarcous elements work simultaneously and harmoniously, 

 the transverse sarcous elements shortening when the longitudinal sarcous elements elongate, and vice versd ; how the 

 VOL. I. 2 ^ 



