The pulmonary trunk was structurally similar to the elastic type artery of the ascending aorta, in which smooth muscle cells and fibroblast-like cells were the main cellular components.
The distal portion of the thoracic aorta was structurally identical to that of the mammalian species. The abdominal aorta, a muscular type artery, had more fibromuscular intimal thickening than the coronary artery both in degree and frequency.
The arterial smooth muscle cells in aged roosters displayed many degenerative changes, including pyknosis of the nucleus, cytoplasmic fragmentation, lipid vacuole and lipofuscin pigment.
Immature virus particles were observed in intimal smooth muscle cells, and many mature virus particles appeared in intercellular spaces. Some smooth muscle cells containing virus particles displayed pyknotic and cytolytic changes even in young chickens.