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 withm. More 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 separate 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- 
nla and point at the highest point of the withers, 
leaving one to suppose that this is the original 
