558 LIVERPOOL VETERINARY MEDICAL ASSOCIATION. 
occasional muscular twitcbings, exhibited when the animal is backed, 
to impotence to perform retrograde movement. 
Shivering may be defined as irregular contraction or twitching 
of a certain set of voluntary muscles manifested during retrograde 
motion, but, like chorea in man, it does not appear that the affected 
muscles are wholly withdrawn from the government of the will; 
there is no loss of consciousness and no defect of volition. Dr. 
Elliotson considers that chorea is due to morbid excitability of the 
medullm oblongata and spinalis, and is essentially a want of har¬ 
mony between the cerebral and spinal acts—volition and sensation 
being perfect, voluntary motion abnormal. Chorea has some other 
points of similarity to shivering—it is hereditary. When local, it 
remains throughout life; the spasm is usually only induced during 
attempt at movement or during excitement. Unlike shivering, 
however, general chorea attacks the young, and recovery, though 
slow, frequently takes place ; in other cases it degenerates into 
hemiplegia. As far as my experience goes, sliivering always in¬ 
creases with age and work, and in some few cases of long standing 
the subjects appeared to be almost paralysed in all movements of 
their hind extremities. The seat of the remote cause of shivering 
is by many supposed to be in that portion of the cerebrum which 
is considered to govern muscular movement; indeed, the only 
authentic mention I can find relating to this disease is a statement 
made by the celebrated physiologist Magendie, who avers that he 
has opened the heads of horses incapable of backing, and has 
always found in the lateral ventricles of their brains collections of 
serous fluid, which must have compressed and even disorganized 
the corpora striata. I may here remark, en passant, that 
Magendie states, if the white matter of the corpora striata be cut 
or otherwise irritated the animal darts forward, or if prevented 
from so doing by the interposition of an obstacle a progressive 
attitude is maintained. This assertion mav assist us in diagnosis of 
the situation of tumours on the brain. 
It is believed that the lobes of the cerebrum have no direct in¬ 
fluence upon the performance of muscular movements, but near 
the base ot the brain on either side there are two large tracts of matter 
which together perform in a modified degree the true funetions of 
the spinal cord. The former of these, the thalami optici, are 
terminations of the superior (sentient) columns of the cord; the 
latter, corpora striata, hold on the one hand a similar relation to the 
superior columns, and on the other are assumed to receive the more 
direct impulses derived from the special functions of the cerebral 
lobes, and transmit the impressions along the cord to the special 
group of ganglionic cells, whose action calls into play the set of 
muscles which are to determine the desired movement. But in 
addition to this special function the thalami are the supposed seats 
of common sensation, and hold the same relation to all the sentient 
nerves of the body as the centres of any other special sense do to 
the nerves of specific function which terminate in them, with this 
dillerence that instead of each sentient filament from the whole 
