498 VOLUNTARY MOTION- 



facts show that motion will occur when the brain is removed 

 and there can be no sensation. Yet when the brain exists and 

 in healthy force, that the will does co-operate with this local 

 excitement of nerves of voluntary motion by those of sensation, 

 when we might not be disposed to believe it, appears from the 

 curious facts mentioned at pages 486-491. showing that sens- 

 ations may occur, and the will may be exercised, almost uncon- 

 sciously. While the brain exists and the system is in health, 

 these motions do not occur without will, or without sensation 

 should the will be overpowered. 



Involuntary muscles have generally a faint red colour, 

 tolerable firmness, fibres small and rather interwoven together, 

 blood-vessels and nerves comparatively numerous and small, and 

 seldom a tendon: while voluntary muscles have generally a deep 

 colour, comparatively soft consistence, their apparent fibres large 

 and generally parallel, comparatively few and large blood-vessels 

 and nerves, and commonly a tendon. 11 



Involuntary muscles are said not to contract suddenly on 

 division, and to perform not one sudden but several contractions, 

 when stimulated ; whereas voluntary muscles, when divided or 

 stimulated, contract suddenly. 



Involuntary muscles are said to have more nerves propor- 

 tionately than the voluntary. 



Like all other parts, muscles require a supply of arterial blood ; 

 and this is proportionate not only to the bulk of a muscle, but to 

 the force and duration of its action. If venous blood is sent to 

 the brain, we have seen that death ensues, and the function of 

 any part is arrested by forcing venous blood into its arteries : 

 this not only not supplying the place of arterial blood, but acting 

 as a poison. Muscles, however, retain their excitability after 

 their supply of arterial blood is cut off, as when they are se- 

 parated from the body. " In the Stenomian P experiment, para- 

 lysis of the hind legs commonly follows the application of a 

 ligature upon the abdominal aorta." But this does not show 

 the excitability of the muscles to be impaired ; they would doubt- 

 Jess contract immediately after the experiment, upon the appli- 



n Dr. Fletcher, I.e. P. 1. p. 109. 

 Bichat, Recherches Physiologiques. 

 p " Steno. Elementar. Myologice Spec. Florent. 1667. 4to. p. 86." 



