FUNCTIONS OF THE CEREBRUM. 521 



strain ; as when we burst into laughter at some ludicrous image presented 

 to the mind, either by a present sensation or by an act of the Memory 

 or Imagination, notwithstanding the strongest inducements presented by 

 "time, place, and circumstance" to a preservation of our gravity. 

 The distinctness of the character of Emotional and Volitional move- 

 ments is further evident from this, that cases of paralysis not unfre- 

 quently occur (especially in the facial nerve, through which most of the 

 muscles of "expression" are excited to action), in which the muscles are 

 obedient to one class of impulses, while the other exerts no power over 

 them. Thus, in one instance, the muscles of one side of the face were 

 palsied in such a manner, that the patient could not voluntarily close 

 his eye, nor draw his mouth towards that side ; yet when any ludicrous 

 circumstance caused him to laugh, their usual play was manifested in 

 the expression of his countenance. And in another case, the muscles 

 were obedient to the will; but when the individual laughed or cried 

 under the influence of an emotion, it was only on one side of his face. 

 To these may be added another case, in which the right arm was com- 

 pletely palsied, so that the individual had not the least voluntary power 

 over it ; yet it was violently agitated, whenever he met a friend whom he 

 desired to greet. The influence of an undue tendency to Emotional 

 excitement, is remarkably seen in what are ordinarily termed Hysterical 

 states of the system ; in which violent convulsive paroxysms are fre- 

 quently brought on by the most trivial causes, if these should call the 

 passions or affections of the mind into undue activity. There can be no 

 doubt that many of the peculiar actions performed by the subject of 

 what is termed Mesmeric influence, are the result of a condition of this 

 nature. There appears to be, in such persons, a proneness to activity 

 of the consensual and emotional parts of the nervous centres, which 

 manifests itself most strongly when the control of the will is withdrawn ; 

 and thus very slight impressions produce very powerful involuntary 

 movements, especially when this response is favoured by the strong 

 desire, on the part of the patient, to exhibit any particular manifestation 

 that is known to be expected by the bystanders. 



918. It has been supposed by some, that the Emotional movements 

 of Man and the higher animals may be ranked in the same category 

 with the Instinctive actions of the lower ; and that the Desires of the 

 former are comparable to the instinctive Propensities of the latter. 

 But this comparison is erroneous ; for what we term propensities (among 

 the lower animals) are nothing else than tendencies to perform particular 

 movements in respondence to particular sensations, without any idea of 

 the purpose of the movement or of the object which has excited it ; whilst an 

 Emotion involves an idea of the object which has called it up, and a Desire 

 involves a conception of the object to be attained. The imitative actions 

 afford a good example of the difference between a propensity and a 

 desire. The former is manifested in such imitative movements as are 

 purely consensual ; the sensation, which is the mainspring of the action 

 in each case, exciting a respondent automatic movement, as when we 

 yawn involuntarily from seeing or hearing the action performed by 

 another, or as when children learn undesignedly to perform many of 

 the movements which they witness in adults. This propensity to in- 



