A histological study was made of the quantitative distribution of elastic elements in the aorta of the baboon, Papio doguera. Materials were obtained in East Africa from freshly sacrificed animals as well as from domestic stock, and represented all age groups from a fetus near term to 28 years. Verhoeff's elastic tissue stained sections were prepared from 4 zones from the arch to the bifurcation.
All specimens showed an attenuation of the thickness of the aortic wall as well as a decrease in the number of layers of elastic membranes from the arch to the bifurcation. The attenuation was less prominent in the older and heavier animals. The reduction in the number of elastic membranes at the lower end indicates a reduced requirement for the storage of ventricular energy by the elastic constituents for blood propulsion. Gravitational forces may be instrumental in maintaining blood flow to the lower extremities without additional expenditure of energy of ventricular origin.