Convulsive Movements of the Head.
Convulsive movements of the head as a whole constitute a frequent 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 indulge 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 strangulated hernia, intussusception, or twisting of the bowels. The habit once formed is not easily corrected, so that careful treatment 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 indication 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 skin or mucous membrane. In more than one instance in this college clinic the trouble was corrected by the section of both facial branches of the 5th cranial nerves as they emerged from the infra-orbital foramina.