CH. III.] THE NERVES OF MUSCLES. 89 



arrives, together with the nerve, and excites it to that action, of 

 which, in virtue of its structure, it is capable. 



ii. The same nerve, can at the same time in which it excites 

 the muscle into action, receive an external impression, and 

 transmit it to the brain, there to excite external sensations, 

 without the two impressions as they pass in opposite directions, 

 interrupting each other in their course (126). 



iii. When a nerve is compressed, or divided, in its course 

 between the brain and the muscle to which it is distributed, 

 the latter cannot be excited into action by cerebral impressions 

 until the compression is taken off (128. Haller's ' Physiology,^ 

 §§ 403, 367). 



iv. If the brain be compressed, all sentient actions in the 

 muscles cease, and all actions dependent on them (128). If 

 only a portion of the brain be compressed, then the actions 

 cease in those muscles which receive their nerves from the 

 compressed portion, inasmuch as they can no longer receive 

 conceptional impressions. 



V. A general irritation of the brain, or such an irritation 

 that the origin of all the motor nerves is implicated, must 

 excite disorder of the whole, or of the greater part of the 

 muscular system (128. Mailer's ' Physiology,' §§ 367-8, 568). 

 165, i. If a muscle be directly excited into action by external 

 sensations, the nerve which perceived the latter must move it 

 (129, 131), although the movement may take place through 

 other and far distant branches (127). This is the sympathy 

 of sentient actions in the muscles. Direct sentient actions of 

 this kind frequently take place, as for example, if by a powerful 

 injury the muscles are excited to spasmodic action, or cramps, 

 other sympathising muscles are frequently excited into similar 

 movements. 



ii. When the medulla of the brain is irritated, violent 



lovements may be excited in the muscles by the pain (132, 



Laller's ' Physiology,' § 308), which are sentient actions^ and 



•e produced in the same way as those resulting from external 



jnsations (132). 

 iii. When the mind, by means of spontaneous conceptions, 



lOves the muscles and other parts through them, the con- 

 jeptions must act on the cerebral origin of the nerves which 



jgulate the muscles (130). All kinds of imaginations and 



