The morphology and evolution of the apes and man. With a foreward by Professor G. Elliot Smith.

As far as I able to determine in 2024, Sonntag's book was the first attempt to write a general treatise on what eventually came to be called "human evolutionary anatomy," in the sense of studying the relationship between primate and human anatomy as it has been understood to have evolved. One test of this analysis is that Sonntag's book is the only general anatomical treatise cited in the very extensive bibliography of mostly periodical literature in Aiello and Dean's An introduction to human evolutionary anatomy (2002), which appeared to be the first formal treatise on the subject.