PATHOGENESIS 117 
to one homogenous mass. This mass is riddled 
with tracts and under the now unrecognizable 
ligamentum nuche is an abscess cavity almost 
closed by granulation tissue. The surface of 
the atlas is rough from destruction of its peri- 
osteum and it may be studded by numerous 
vegetations of bony growths. There is found 
sometimes a shredded condition of parts of the 
ligament, parts that have partly loosened from 
necrosis. In some cases, usually in aged horses, 
the ligament is permeated with calcareous de- 
posits, each of which is well incarcerated with 
connective tissue elements. 
Atypical Poll-Evil 
The atypical poll-evil begins with a halter 
abrasion of some kind of wound that 
gives admission to pyogenic microorganisms. 
It is at first a subcutaneous abscess, 
and if carbuncular in character may give 
rise to all of the symptoms of a_ typical 
poll-evil in the phlegmonous stage. This 
form will differ from the typical form in 
that cicatrization will follow evacuation of its 
pus and general slough. If deep and the 
slough should be attached to the ligamentum 
nuche a chronic poll-evil having all of the char- 
acteristics of the other, the typical kind, will 
supervene. In this case the ligament is at- 
