SUMMARY. INVOLUNTARY MOVEMENTS. 301 



tion, appears to have, for its seats or centres, the olfactory lobes and 

 some of the gray masses at the base of the brain, at all events, the 

 optic thalami, and corpora quadrigemina, and also some of the gray 

 matter in the cerebral peduncles, the pons, arid the back part of the 

 medulla oblongata. The olfactory lobes appear to be the centres of 

 the vspecial sense of smell. The visual sense has apparently for its 

 centres, the corpora quadrigemina with the back part of the optic 

 thalami ; the office of the corpora geniculata, in regard to vision, is 

 unknown. The sense of taste resides in the gray matter of the upper 

 part of the back of the medulla oblongata, and the sense of hearing, 

 still lower down, in the same part of the great nervous axis. General 

 or common sensibility is probably diffused through all the gray matter 

 from the base of the cerebrum downwards, at least to the lower part 

 of the medulla oblongata. Whether it should be regarded as extend- 

 ing also down the spinal cord, whilst this remains in connection with 

 the encephalon (an opinion entertained, amongst others by Pfliiger) 

 may well be doubted, if not denied ; for, owing to the condition of 

 things, it cannot be proved, and the retention of excito-motor power, 

 with the cessation of sensibility, which necessarily follow the severance 

 of the cord, are quite explicable on the hypothesis that it is merely a 

 conductor of sensory impressions upwards to the encephalon. As to 

 the special seats or centres of the tactile sense, of the sense of temper- 

 ature, of the common sensibility to pain, and of the muscular sense, 

 the latter of which, however, is supposed by some, to be seated in the 

 cerebellum, and as to the seats of those other and more vague sensa- 

 tions belonging to the vegetative or nutritive system, such as hunger, 

 thirst, nausea, want of breath, &c., we are quite ignorant of their 

 exact locality, although there may be special centres devoted to each 

 or to some of them. 



Voluntary motion. The seats or centres, in which the volitional 

 motorial stimulus originates, are certainly the cerebral hemispheres ; 

 for the will is completely annihilated, when these are removed, or 

 when their integrity, or power of action, is otherwise interfered with. 

 Whilst, however, the will to act arises in the cerebrum, the co-ordina- 

 tion of the various movements of the body, seems to require for its 

 accomplishment, the direct or indirect co-operation of the cerebellum. 



Involuntary motion. Involuntary motion includes movements sug- 

 gested by ideas, idea-motor (Carpenter), emotional movements, instinc- 

 tive, or sensori-motor movements, which are reflex movements of a more 

 general and more highly co-ordinate character, and are accompanied 

 by sensation ; and lastly, the more simple reflex or excito-motor move- 

 ments, which are not necessarily accompanied by sensation ; and which 

 include some governed by the spinal cord, and others regulated, as we 

 have hereafter to describe, by the action of the sympathetic system. 



The ideo-motor, or ideational movements, such as those of laughter, 

 or sadness, produced by ideas passing through the mind, must have 

 their organic centres in the cerebral hemispheres ; so, too, the co- 

 ordinated movements are performed under the influence of ideas arising 

 in the mind, during reverie, dreaming, and somnambulism, when con- 

 sciousness is absent. 



