4-94- VOLUNTARY MOTION. 



to the body; or, if one foot only, that foot only is drawn up. 1 

 He also found that, if the muscles of the leg of a decapitated frog 

 are irritated, almost all the muscles of the lower extremities move, 

 provided the spinal chord is entire; but, if the chord is de- 

 stroyed, the neighbouring muscles remain still, and the irritated 

 muscle itself is only excited to a tremulous motion. k He also 

 noticed that, though the muscles of the thighs were contracted 

 when pricked or cut, neither they nor the neighbouring muscles 

 were nearly so strongly convulsed as when the toes were wounded, 

 the toes having a much more acute sensibility. 



Others have since variously illustrated these facts. Dr. Ma- 

 gendie mentions that, when the posterior roots of the inner 

 side of the spinal nerves are irritated, the signs of extreme 

 pain are accompanied by convulsions of the muscle of that 

 same side only : Mr. Mayo, that, if the head of a pigeon is 

 cut off and all the brain removed except the little to whish 

 the common motor nerve of the eye is attached, and the 

 optic nerve divided and its truncated extremity connected with 

 the brain pinched, the iris instantly contracts : Dr. Macartney, 

 that, if the head of a pigeon is cut off, nay, if even the eye is 

 taken out, light suddenly admitted to the retina produces con- 

 traction of the iris. 



These facts have lately given rise to a speculation that a por- 

 tion of the nervous system exists independent of will, and solely 

 for involuntary actions of what are usually considered volun- 

 tary muscles, by means of impressions, not felt, on nerves usually 

 considered nerves of sensation. A portion of the chorda ob- 

 longata and of the chorda spinalis is fancied to be separate and 

 independent of the rest, and this imaginary part is called by its in- 

 ventor, Dr. Marshal Hall 1 , excito-motory. This physician has 

 made experiments fundamentally the same as those of Sir Gil- 

 bert Blane and his successors. Instead of separating a portion 

 of the body with its corresponding portion of encephalo-spinal 

 substance in which the nerves of sensation and motion meet, 

 he only stupefied an animal. He struck a horse with a pole- 

 axe over the anterior lobes of the brain. It fell as if thunder- 

 struck ; was convulsed, and then motionless. But it soon 

 began to breathe, and continued to breathe freely. When 



1 Observations on Irritability, sect iv. p. 4. k Ibid. 



Phil. Trans. 1833. P. ii. ; and Lectures on the Nervous System. 1836. 



