144 
SPONTANEOUS LUXATION OF THE PATELLA. 
self, by examination of the bones of different horses; and in one 
case that had been the subject of this affliction, there was not the 
slightest projection at that part of the articulating surface of the 
external condyle which opposed itself to the patella when the foot 
was on the ground, and the condyles remarkably small throughout. 
I have bones now in my possession equally wanting this pro- 
trusion at that point ; but 1 have found horses with short quarters 
and straight hindlegs — that is to say, in which the angle formed by 
the femur and tibia was very obtuse — to be generally my patients 
in these cases; and in these shaped animals the patella lies more 
upon this less projecting part of the condyles when not in action, 
and the ligaments of this bone are in a less favourable position to 
retain it in its place. If a relaxed state does occur in the muscular 
system, I am of opinion that no one acquainted with the anatomy 
of these parts will doubt; but that this undue performance of the 
functions of the muscles inserted into this bone would more easily 
admit of its displacement, if the natural predisposing cause, the 
want of a sufficient degree of convexity of the condyles, should at 
the same time exist. I believe it to be generally admitted, that 
when nervous energy is diminished by disease, or any other cause, 
a want of tone in the muscular system is the effect. I am, more- 
over, of opinion, that it usually takes place when the muscles are 
in a passive state, or when the vis insita is in the least degree 
exerted, as I have noticed from the information that I have re- 
ceived, when called in to attend such cases, that the animal was 
invariably found standing in this state, and the dislocation only 
discovered to have taken place when an attempt was made to move 
them (except the leg was projecting backwards, from having tried 
to move himself forward after it had occurred), and never to have 
been observed to take place when the animal was in motion, or in 
the act of getting up or lying down, unless soon after the reduc- 
tion of a previous dislocation of it, when the most probable means 
of again displacing it is by turning the animal towards the side 
affected. It must, however, be considered that the causes which 
originally favoured the luxation still existed. 
These remarks are made from strict observation of the indivi- 
dual circumstances connected with all cases of this description that 
have come under my notice, and not from any visionary or specu- 
lative opinion. I do not conclude that the case (that of M. Conte) 
which stimulated me to enter on this subject was one of luxation 
of this bone, spontaneous or accidental, in either case the symp- 
toms being alike, except when it takes place inwardly *, which I 
have never seen; nor do I believe it could be, except from me- 
* Mr. Cherry relates a case in “ The Ilippiatrist,” in which the displace- 
ment took place inwards. — Ed. 
