It was when the author of this book was working in the Department of Human Anatomy at Oxford University that Prof. W.E. Le Gros Clark encouraged him to study the vascularization of the brain. Le Gros Clark, who has an international reputation for his research on the diencephalon, may thus be regarded as one of the initiators of this investigation. The prese!1t work is born of the happy coinicidence of a number of circumstances, namely, the author's possessing detailed anatomic knowledge and suitable techniques of carrying on research, and present the results, great patience, inventiveness and a special talent for dealing with highly complex material. It is necessary to know all this in order to understand how the author of this monograph was in the position to do such painstakingly detailed research on a subject of extreme complexity and to present it here in graphic and written form. The atlas fills a long felt want among neurosurgeons and researches in neuroana tomy as regards both the form and position of the nuclei and fiber tracts of the upper brain stem and the type and arrangement of its finer vascularization.