772 
W. J. MARTIN. 
scription need be given here of the muscles, bones and liga¬ 
ments involved in this disease. 
Etiology .—The causes of fistula are often obscure. In many 
cases fracture, or bruise of the superior spinous process of the 
dorsal spines or necrosis of the tuberous ends of the same, al¬ 
most invariably gives rise to it. Injuries to the dorsal spines 
are generally caused by the animal rolling upon some hard sub¬ 
stance, such as a stone in the pasture or in getting cast in a nar¬ 
row stall. Running against low shed or barn doors, low hang¬ 
ing timber of trees in the pasture, are often prolific causes of 
this disease. It is often caused by the animal’s skin being in¬ 
fested by parasites, such as the sarcoptes equi , dermatodectes 
equi , and other itchy skin affections, which cause the animal to 
rub its neck and shoulders in a violent manner against fences 
or the corners of buildings. Horses at pasture, more especially 
young animals, are much given to the habit of playfully seiz- ' 
ing each other with their teeth over the withers ; thus produc¬ 
ing- an abscess and often a fistula. Anatomical confirmation of- 
o 
ten plays an important part in the cause of this disease. Horses 
whose dorsal spines are abnormally high and ragged, are much 
predisposed to this disease ; again, heavy draught animals, 
whose withers are low and broad, are likely to have the parts 
excoriated by the saddle-tree of the harness slipping forward 
while engaged in drawing heavy loads. In text-books on veter¬ 
inary medicine and surgery, the most common cause of fistula 
mentioned is that caused by an ill-fitting saddle. This, I have 
no doubt, is in the main correct, though in the section of coun¬ 
try in which I reside, horses are seldom used for saddle pur¬ 
poses ; still, fistula of the withers is quite common. 
Fistula may also make its appearance as a sequela to attacks 
of influenza, purpura hsemorrhagica or in general debility in 
which the animal’s blood is left in a vitiated condition. I can 
recall to mind one instance in practice, in which, during one 
week, there came under my care six cases of fistula, all of 
which had recovered but a short time previously from influenza. 
From this it would appear that the septicsemic product of a 
