38 FISTULA AND POLL-EVIL 
usually due to harness bruises, reflects more 
upon that part of the region occupied by the 
supraspinous ligament. The disease pro- 
gresses in many cases from one to the other of 
these two structures by extension of the dis- 
ease process in one direction or the other 
according to the initial seat. That is to say, a 
fistula beginning in a cyst at the level of the 
second dorsal spine may attack the liga- 
mentum nuche above that level and then 
travel backward into the supraspinous liga- 
ment, while on the other hand a harness bruise 
may cause a disease of the supraspinous liga- 
ment at the level of the saddle seat that will 
travel forward into the ligamentum nuche. 
In fact, all old cases have this dual involvement 
and often the spines beneath are found necrotic. 
The Typical Form 
To make our study more comprehensive we 
shall divide the development of this form of 
fistula into three stages, namely: The saccu- 
lar stage, the phlegmonous stage and the 
fistulous stage. 
1. Saccular Stage. This is the initial one. It 
has its origin in the accumulation of serosity 
upon or adjacent to one of the dorsal spines, 
usually the second. Beginning with this col- 
lection of serum, which is sero-fibrinous in 
