Abstract
Differences in the phonetic mechanism between monkeys and humans were studied using 6 adult Japanese monkeys. Their vocal cords were fixed with formalin and cut along and across the axis. Some of the samples were treated with 10% NaOH to dissolve cells and elastic fibers, and some of them were treated with 90% formic acid to consume cells and collagen fibers. Each sample was then fixed with OsO4, dehydrated, dried at the critical point, ion-coated, and studied under a scanning electron microscope. Both collagen fibers and elastic fibers mostly ran straight, and their density was higher in upper layers, but little regional difference in the fiber properties was noted. In the muscle layer, connective tissue surrounded muscle fibers were scarce. From these findings, the fibrous structure of the monkey vocal cord is much simpler than that of human vocal cord, and this is considered to reflect the short and monotonous phonation of monkeys.
