342 



HITCHCOCK'S ANATOMY 



609. To secure Precision in all Voluntary Actions. 



— In Draper's Physiology is found another hypothesis for the 

 division of the brain into two parts : this is to secure precision 

 in the efforts of the intellect and will. u For there is no 

 doubt, 77 he says, u that the hemispheres have not only the 

 power of acting separately, but also conjointly ; thus there is 

 no student but must have observed, when busily engaged in 

 reading, that his mind will wander off to other things, though 

 he may mechanically cast his eye over page after page ; and 

 the same may occur in listening to a lecture or sermon. But 

 though the insane man may indulge in two synchronous trains 

 of thought, he never indulges in three, for the simple reason 

 that he has not three hemispheres to do it with, the same re- 

 mark applying to the sane man in the accidental wandering 

 of his thoughts. 77 



010. Thought, Memory, and the Reasoning Powers 

 require a Sound Brain. — As already mentioned, the brain 

 is not the seat of motive power : this does not originate here, 

 although voluntary movements are controlled by it. But 

 automatic or reflex movements, such as the twitching of the 

 muscles of the leg and foot, when the sole of the foot is 

 tickled with some slightly irritating substance, are entirely 

 beyond the control of the cerebrum or will, since they take 

 place nearly as well in a person who is asleep or stunned by 

 a blow, or even when the nerves of sensation and motion are 

 paralyzed. Thought, memory, reasoning, and all the intel- 

 lectual states demand a healthy and a sound brain for their 

 perfect action, w T hile the ordinary muscular movements and 

 the functions of respiration, circulation, and digestion, are 

 dependent upon the Spinal Cord, Sympathetic Nerve, and 

 Cerebellum. 



611. Definition of Sleep.— Need of Sleep. — Sleep, 

 " tired nature 7 s sweet restorer, 77 is a state of the body, in 



609. How can two hemispheres secure a precision in voluntary actions ? 610. Are 

 reflex movements under the control of the brain? What powers of mind are dependent 

 on the cerebrum ? 



