Prof. Dr. H(enricus) H(ubertus) Janssen (1910–1982) was a Professor of Latin at De Katholieke Universiteit Nijmegen from 1938–1967. He was also involved in Dutch politics serving as Staatssecretaris van Onderwijs (1962–3) in the cabinet of Jan de Quay (Katholieke Volkspartij). He wrote mainly about Latin literature, especially Christian authors, but also produced a small edition of Oscan and Umbrian inscriptions with Latin translations. The work pictured on the left is the first of a two volume work (part II on morphology appeared in 1957). It is not nearly as rare as the other books I mentioned—it's available at 7 libraries in the U.S—but because it's written in Dutch it is probably not as well known as it should be. There are two notable features of this book: (1) The phonology-section is introduced by a discussion of classical structuralist terminology and a structuralist approach is evident throughout volume 1. Although this is a historical grammar, it is definitely not a comparative grammar. The IE background is not discussed at all. (2) There is a lengthy and well organized section on word formation. This book is still used in Nijmegen.