MUSCULAR MOVEMENTS. 445 



is not affected by acetic acid or by boiling with caustic soda. 

 It is not softened by heat, by prolonged boiling in water, 

 but is slowly dissolved, without decomposition, by sulphuric, 

 nitric, and hydrochloric acid, the solution not being precipi- 

 table by potash. Its organic base is a nitrogenized sub- 

 stance called elasticine ; l containing carbon, hydrogen, oxy- 

 gen, and nitrogen, without sulphur. This is supposed to be 

 identical with the sarcolemma of the muscular tissue. 8 



The purely physical property of elasticity plays an im- 

 portant part in many of the animal functions. TVe have 

 already had an example of this in the action of the large 

 arteries in the circulation, and in the resiliency of the paren- 

 chyma of the lungs ; and we will have occasion, in treating 

 of the functions of other parts, to refer again to the uses of 

 elastic membranes and ligaments. The ligamenta subflava 

 and the ligamentum nuchse are important in aiding to main- 

 tain the erect position of the body and head, and to restore 

 this position when flexion has been produced by muscular 

 action. Still, the contraction of muscles is also necessary to 

 keep the body in the vertical position. 



Muscular Movements. 



Muscular movements are observed only in the higher 

 classes of animals. Low in the scale of animal life, we have 

 the contractions of amorphous substance and ciliary mo- 

 tion ; and in some vegetables, movements, even attended 

 with locomotion, have been observed. These facts make the 

 absolute distinction between the two kingdoms a question of 

 some difficulty ; but in animals only do we have separate 

 muscular systems. 



The muscular movements capable of being excited by 

 stimulus of various kinds are divided into voluntary and 

 involuntary ; and generally there is a corresponding divi- 



1 See vol. i., Introduction, p. 91 



9 ROBIN ET YERDEIL, Traite de chimie anatomique, Paris, 1853, tome iii., 

 p. 364. 



