PATHOGENESIS 45 



jacent structures, coming to the surface very 

 slowly. It is, in fact, a cold abscess. Some 

 months may elapse after infection has occurred 

 before the abscess points at the surface, but all 

 of the while ^pathological changes are taking 

 place within. JMore connective tissue is formed 

 and the necrosis of the ligament is extending 

 forward and backward from the seat of the 

 abscess which was originally the cyst. Soaked 

 in this infected environment the dorsal spines 

 become involved and sej^arate from the soft 

 structures attached to them, sometimes stand- 

 ing out stump-like into the cavity until seques- 

 tration occurs. Slowly the pus finds an exit 

 at the surface of the body after burrowing here 

 and there in different directions. The exit 

 aperture is not uniformly located. It may 

 sometimes appear at the summit of the enlarge- 

 ment, but more often it is more remote, the pus 

 having traveled between the different layers of 

 fascia and muscular tissue of this complex- 

 region to places far removed from the initial 

 hot-bed. We once traced a fistulous tract from 

 the lumbar region forward along the longissi- 

 mus dorsi, under the scapula to the level of the 

 second dorsal vertebra. Other cases burrow 

 backward under the cervical angle of the scap- 

 [da and point at tlie highest point of the withers, 

 leaving one to suppose that this is the original 



