74 DISEASE IN WILD MAMMALS AND BIRDS 
the aortic valves and from which the main vessels spring, 
is practically always free of lesions which are on the other 
hand most marked in the thoracic and abdominal sections. 
One's attention is usually attracted to the aortic surface 
by its roughness although visibly there may be no plaques, 
but upon close inspection a mottled opacity may be 
detected. This all seems due in the few cases subjected to 
tissue section, to hyperplasia of endothelia, with or with- 
out fibre increase. The media may show muscular granu- 
larity or no change at all. At the stage when plaques are 
formed, fairly well outlined, firm but rather brittle, 
raised areas are detected, seated upon a distinctly opaque 
gray wall. The remainder of the vessel may be smooth 
and elastic but sometimes, in the Accipitres for instance, 
a general resistance to pressure and tension is found. 
Microscopically such a vessel will show a media the seat 
of ruptured muscle fibres, split-up or broken elastica and 
some debris, while the intima is covered with active and 
distinct fibrocellular exudate. 
I have for comparison divided the cases into those in 
which the superficial productive character was prominent 
and those seemingly entirely a degeneration of the media, 
that is vdth inactive intima. In mammals 77 per cent, of 
the cases were of the degenerative type while in birds 
50 per cent, were of this kind. The exact importance of 
this difference is not easy to evaluate, but with 
the facts that the bird has a greater elastic supply 
for its large vessels and a greater wall-to-caUbre ratio, 
it is interesting. The aorta alone was affected in half of 
the birds, the remainder showing lesions in the carotids 
and femorals. 
The tendency for the media to degenerate would lay 
the basis for concavities on the intimal surfaces after the 
type seen in Monckeberg's sclerosis. A number of cases 
of this variety have been encountered, but instead of 
being better developed in the vessels of extremities as in 
man they have presented more definite pictures in the 
