Nature of phenomenon, arhythmic, hyperexcitability of nerve centres or
skin. Nerve section. Head jerking: =horse=, hard bit, severe check,
internal pain, exertion, hypersensitiveness. Treatment: nerve section.
Tongue lolling, etc. Flapping of lower lip. Nasal rhythmic movements.
Weaving, from impatience, rhythmic. Rocking on hind limbs. Resting
foot on coronet. Pawing. Treatment: eliminate irritation, nerve
tonics, sedatives, hygienic measures.
This has been observed especially in the dog and may be easily
confounded with chorea. The muscles on one side of the face, are
twitched at more or less regular intervals, or in other cases there are
sudden opening and closing of the lower jaw. 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
hyperexcitability 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 excited 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 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 5^{th} cranial nerves as they emerged from the
infra-orbital foramina.
Abnormal Movements of the Tongue.
Some horses double the tongue downward, others upward of the bit; others
protrude the tongue and give it a sinuous, serpentine motion which
causes alternate protrusion and retraction.
Flapping of the Lower Lip.
This habit of rapid opening and closing of the lower lip so as to
produce a disagreeable flapping noise by striking it against the upper,
is seen in many horses and proves a most objectionable trait in harness
or saddle animals.
Rhythmical Movements of the Nose.
Certain horses apply the protractile end of the nose against the lower
lip and spend hours in succession in moving it rhythmically forward and
backward, or from side to side.
Weaving. Movement like a Bear in a Cage.
This consists in a lateral rocking of the head and neck, and sometimes
of the chest as well with alternate stepping on the right and left fore
feet. It has been supposed to represent the movement of the weaver in
working a hand loom, or still better the movement of a caged wild beast
in constant turning toward the right and left of the front of his cage.
The motions are as regular as a pendulum, and involve the contraction of
corresponding groups of muscles on the two sides of the body.
They seem, in some cases, to begin in impatience in waiting for the
feed, while other horses in the same row are being attended to first,
but when the habit has been formed it may be continued most of the time
in the intervals between feeds as well. Nervous horses and those that
are hearty feeders are the most subject to this infirmity.
Disorderly Movements of the Limbs.
Some horses have a habit of continuously raising one hind limb, others
raise the right and left alternately, rocking the hind quarters from
side to side, others stand with the heel of one hind foot resting on the
front of the coronet of the other, while still others paw continuously
with the fore feet while standing in the stall.
_Treatment._ These various conditions even when begun as an expression
of impatience, soon become fixed habits, that prove in the end virtually
uncontrollable by an animal, which has no strong will and no
consciousness of anything to be gained by resisting the impulse. They
become virtual psychoses. In cases in which the habit can be traced to a
peripheral irritation, the cutting off of this by complete section of
the afferent nerves leading to the irritable nerve centre will sometimes
succeed in effecting a cure. In other cases in which the source of the
disorder is probably largely central in the cerebral ganglia, nerve
tonics, and sedatives, and generally corroborative treatment are the
most obvious means of palliation. Such measures are, however, rarely
successful. Nourishing food and invigorating outdoor exercise are useful
auxiliaries.