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 nucha 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 nuchge. 

 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 



