Convulsive Twitching of the Face. 67 



The affection has not been satisfactorily connected with any- 

 special brain lesion, though as in chorea proper and epilepsy, we 

 must invoke a special disorder or hyper-excitability of the nerve 

 centres presiding over the affected muscles. The clonic spasm 

 may in some cases be due only to a motor impulse from such ex- 

 cited nerve centre, while in others it may be traced backward 

 along the afferent nerves to an oversensitive part of the skin or 

 other organ. In these last purely reflex forms of the trouble it 

 may be possible to correct it by section of the sensory nerves 

 involved. 



Convulsive Movements of the Head. 



Convulsive movements of the head as a whole constitute a fre- 

 quent form of chorea in the dog. It is especially common in 

 horses and shows itself in different forms. A horse with a 

 tender mouth, or which has been used with a hard bit, or with a 

 heavy hand on the reins, or which has been driven with a check 

 rein so short as to be unsuited to its conformation, is liable to in- 

 dulge in annoying elevation and depression of the head when 

 under the saddle or in harness. The same phenomenon may be 

 shown in connection with violent internal pains, as in strangu- 

 lated hernia, intussception, or twisting of the bowels. The 

 habit once formed is not easily corrected, so that careful treat- 

 ment with the view of prevention is especially to be given. 



Another more objectionable, dangerous, and less voluntary 

 motion is the sudden jerking of the head upward, or to one side 

 when excited under the saddle or in harness. The disorderly 

 movements are not, as a rule, seen while the animal is at rest, 

 but seem to be produced under the stimulus of exertion. They 

 appear to be quite involuntary, and suggest the dread caused by 

 the settling or buzzing of an insect about the nose or ears, but 

 occur in the depth of winter in the absence of insect life, as well 

 as in midsummer. The suddenness and involuntary nature of 

 the movement is suggestive of epilepsy, but there is no indica- 

 tion of attendant unconsciousness. From choreic movements it 

 is apparently distinguished, by its presence only when ridden or 

 driven. It is unquestionably associated with hypersensitiveness 

 of the nerve centres, and yet in many cases it appears to be a 

 reflex originating in a specially tender or sensitive part of the 



