C. STOUT AND F, BOHORQUEZ 
845 
Figure 1. — (Z 512) Aardvark (Orycteropus axer). 
Adult female. Thoracic aorta showing numerous 
fatty streaks. Sudan IV stain. 
parently due to foci of medionecrosis. No 
acutely necrotic smooth muscle cells were ob- 
served, but these cells were absent in large 
areas of the involved media, leaving sheets of 
hyalinized tissue containing sparse elongated 
nuclei. Elastic fibers at the margins of the aneu- 
rysms were fragmented, closely aligned, and 
often clumped and coiled in tangled masses 
(Figure 9). The intima overlying the aneu- 
rysms was greatly thickened and hyalinized, but 
no mural thrombi were present. 
Somewhat different lesions were found in the 
thoracic aortas of an adult male tamandua 
(Tamandua tetradactyla) and an adult male 
Patagonian cavy (Dolichotis patagonium). 
These lesions were also associated with multiple 
saccular aneurysms. Histologically, the lesions 
consisted of focal areas of degeneration and cal- 
cification of the smooth muscle elements of the 
inner media. The elastic fibers remained unal- 
tered within these areas of calcification, except 
for the most central portions, which were com- 
pletely replaced by granulation-like tissue (Fig- 
ure 10) . 
Medial lesions of a different character were 
present in several species of hoofed mammals. 
These lesions usually occurred in the lower 
thoracic aortas, producing a gross picture of 
narrow longitudinal bands of transverse 
ridges. In one elderly female wapiti ( Cervus 
canadensis), the proximal inferior mesenteric 
and celiac arteries were transformed into wash- 
board-like structures by this process (Figure 
11) . Microscopically, the elastic fibers seemed to 
be affected first, appearing swollen and contain- 
ing stippled calcium deposits. Later, the entire 
inner media was replaced by areas of hyaliniza- 
tion with focal calcification. Contraction of the 
involved tissue apparently produced the trans- 
verse ridges that were visible to the naked eye. 
The etiology of the three types of medial le- 
sions described above was not obvious. Parasitic 
Figure 2. — (Z 497) Chimpanzee (Pan troglodytes). 
Nine-year old female. Entire aorta showing 15% 
fatty streaks. Sudan IV stain. 
