290 PHENOMENA OF MUSCULAR MOTION. 



over the belly of a muscle during its contraction, or when the 

 end of the finger is introduced into the auditory meatus. During 

 the contraction of a muscle there is no change in its color, nor any 

 increase in the amount of blood thrown into it by the arteries as 

 was once supposed. 



Fig. 71.* With the aid of the microscope it is easy 

 to distinguish the manner in which the 

 contraction of a muscle is effected. Fig. 

 70, exhibits a magnified view of the mus- 

 cular fibres in a state of relaxation. When 

 they contract they form suddenly a num- 

 ber of zigzag flexions, or angular undula- 

 tions, opposite each other, as seen in fig. 

 ' c 72, page 291, according to the observation 

 of Edwards,! Prevost, and Dumas. By 

 repeated experiments, these gentlemen 

 have determined that the flexures of each 

 fibre take place at certain determined points, and nowhere else. 

 These points are precisely at the places where the nerve a, the 

 trunk of which runs parallel with the muscular fasciculi, sends 

 off its filaments to traverse the muscular fibres, at the spot where 

 the angles of the undulations are formed. These nervous fila- 

 ments after having continued their course for some time, are 

 reflected in the form of loops, and return towards the brain, so 

 as to constitute with that organ a continuous circle. 

 During the contraction of the muscle its extremities ap- 

 proach, for though the absolute length of the fibre remains the 

 same, the distance between its extremities is diminished by the 

 undulations. The will transmitted through the nerves is the 

 usual stimulus, which excites the voluntary muscles to con- 

 traction. Galvanic electricity, or disease of nervous centres 

 will produce the same result ; that of the involuntary muscles, 

 usually results from the impression made upon the organs, as 



* a, Nerve, b b, Fasciculi of muscular fibres which are straight and parallel. 

 e, Nervous filament which separates from the nerve a, and crosses at right 

 angles, and at regular distances, the muscular fasciculi. 



f Elements de Zoologie, etc., par M. H. Edwards. Paris, 1838. 



