38 THE HUMAN BODY. 



would not be sufficient to supply space for them ; this direct 

 attachment to large surfaces is confined to a few only, the 

 others being attached by their aponeuroses or tendons to 

 limited spaces. 



The muscles are at the same time contractile and exten- 

 sible. The muscle shortens by contraction and increases 

 in thickness at the same time that its' length diminishes; in 

 .repose it is soft and yielding to touch, in contracting it 

 becomes hard and resistant. These successive changes are 

 easily demonstrated by applying the hand to the course, of 

 a superficial muscle, on the front of the arm for example, on 

 the biceps. When the fore-arm is extended it projects but 

 slightly and yields to pressure; it swells, on the contrary, 

 becomes resistant, and forms a marked protuberance, when 

 contracting in order to flex the fore-arm. 



The contraction of a muscle may also take place without 

 its being shortened. When, for example, the fore-arm is 

 extended upon the arm, if the extensors oppose the flexion 

 by contracting, the biceps and anterior brachial, both flexor- 

 muscles, may contract without their ends approaching each 

 other. 



Glisson, Borelli, and other anatomists have supposed that 

 the muscle increases in volume during contraction; but further 

 experiment, confirmed also by those of Provost and Dumas, 

 has demonstrated that it gains in thickness only what it loses 

 in length, and that there is no change in the absolute volume. 



In contracting, the muscular fibres become tortuous and 

 wavy, wrinkles are formed on the surface, a sort of trembling 

 pervades the whole mass, and its temperature is raised. 

 Becquerel and Breschet have observed this increase to reach 

 half a degree centigrade. 



To the contraction of certain muscles must correspond 

 the inertia or even lengthening of the antagonistic muscles, 

 as for instance when the fore-arm is flexed upon the arm or 

 the leg upon the thigh, the extensors of the fore-arm and of 

 the leg take part in the movement and lengthen by means 

 of their extensibility. In like manner the muscular texture 

 which forms the walls of certain organs, as of the stomach and 

 intestines, is expanded by the fluids and the aliments, or by 



