36 



THE MUSCLES 



are being used, as at the bend of the elbow or knee. The 

 largest tendon of the body is that which is inserted into 

 the heel, called the tendon of Achilles, after the hero of the 

 Grecian poet, the fable relating that it was at this point that 

 he received his death-wound, no other part of his body being 

 vulnerable. (Fig. 15.) The muscles in 

 the front part of the thigh unite to form. 

 a single and very powerful tendon, and 

 enclose a small bone called the knee-pan, 

 which, acting like a pulley, greatly in- 

 creases their power, and at the same 

 time protects the front of the knee-joint 

 (Fig. 16). 



6. Muscular Contraction. The muscles, 

 when acted upon by the appropriate stim- 

 ulus, contract, or so change their shape,, 

 that their extremities are brought nearer 

 together. The bending of the arm, or of 

 a finger, is effected in this manner, by the 

 will ; but the will is not the only means 

 of producing this effect. Electricity, a 

 sharp blow over a muscle, and other stim- 

 u ^> a ^ so cause it. Contraction does not 

 always cease with life. In man, after 

 death from cholera, automatic movements of hands and feet 

 have been observed, lasting not less than an hour. In certain 



over the instrument incessantly changes its position. Sometimes a single 

 finger produces an isolated note ; sometimes two or three act simultane- 

 ously to produce a concord ; while a fourth, striking a string with increas- 

 ing rapidity, produces a trill which rivals the nightingale. Add to all 

 these the modifications necessary to swell the sound or let it die away 

 all, in a word, that constitutes musical expression, and it will be admitted 

 that this mechanism is allied to the wonderful, and that it surpasses the 

 most perfect productions of human art." A further idea of the rapidity 

 of the hand's movements is given in the playing of a skilful pianist, whose 

 hands, oftenest occupied together, produce on an average six to eight 

 notes at a time, or about 640 notes in a minute in medium time, and 960 

 notes in extremely quick time. The Wonders of the Human Body. 



FIG. 15 

 LOWER PORTION OF THE LEG 



6. Contraction of the muscles ? Bending of the arm or finger ? Other agencies ? Auto- 

 matic movements ? In cold-blooded animals ? 



