The facts presented in this work will contribute to our understanding of the highly developed and intricately arranged facial musculature of monkeys and humans. Through the treatment and utilization of the material, the reader may gain insight into the nature of the transformations that this anatomical area underwent in primates. Those who seek to learn only a series of new observations may primarily refer to the eight accompanying plates; however, those who see the value of scientific research in explaining the actual will have to make the effort to follow the author's line of thought and sift through the somewhat extensive text. This book, which contains studies on the facial musculature of primates, is an unaltered reprint of the original edition from 1887.