146 
SPONTANEOUS LUXATION OF THE PATELLA. 
an extension, still this state can be, and is, occasioned by an ex- 
treme action in muscles whose antagonizing power is, pro temp., 
destroyed. The flexion of the fetlock is, in all the cases that I have 
seen, to be accomplished to a greater degree by manipulation than 
it is, in this state, by the action of the muscles; for although it is 
flexed, I have never found it to that extreme degree described by 
Mr. Percivall; and, with regard to the increased sensibility of the 
skin, might not this appear in the limb generally ] I have ob- 
served not only this tenderness, but apparent fear when the limb 
is interfered with. It may appear strange, if the case described 
by M. Conte were luxation, that it should be reduced without as- 
sistance. I have seen the patella slip off and on twenty times in 
a day. In such cases, Mr. C. Percivall, the only authority who 
has given us any enlightenment upon this subject, does not appear 
to think that they occur from any natural predisposing causes in 
the animal, or are produced by muscular relaxation as the imme- 
diate cause ; but he has, undoubtedly, seen many cases, the cause 
of which (from his own relation of them) he appears to hold in 
doubt. Still, attributing them to some injury from external causes, 
he states, “ having seen these cases chiefly in India, I believe it of 
more frequent occurrence there than in this country, probably aris- 
ing from the peculiar manner in which the horses are tied up, their 
heads being confined by side-ropes to pegs driven into the ground, 
while the hind legs are encircled in leathern straps and confined by 
ropes in a similar manner to two other pegs at about five or six 
yards distance from the feet. The dislocation seems to happen either 
in lying down or from some violent effort made in rising; and on 
other occasions it happens out of the stable, either in consequence 
of some external injury, or from some sudden or lateral movement 
for which the muscles at that time were unprepared*.” Now this 
authority, to which I pay great deference, does not state whether he 
has ever been positively aware of its having occurred in the act of 
rising, that is to say, has it been noticed by any one immediately 
after a horse raising himself from the ground, or has he ever had 
a case where the animal was lying down. If he has not, I think it 
very improbable to have occurred during these movements; for if the 
limb is flexed, which is generally the case when the animal is in 
these positions, it is then most favourably situated to retain this 
bone in its articulation. 
1 have had three of these cases within the last twelvemonths, 
all of which were in four-year-olds; two of them after an- attack of 
influenza, and the other when the mare had been turned out, after 
being my patient some time with a punctured foot. In neither of 
From Mr. Percivall’s “ Ilippopathologv,” vol. i, p. 278 . — Ed. 
