Some anatomical aspects of the blood supply of the brains of mammals have been examined to illuminate their functions. A fundamental explanation of sudden infant death syndrome (cot death) is suggested following experimental observations. Speculative contributions have been made to comparative physiological ideas concerning mammals of pronograde and erect habitus, their vascular pressure adaptations and temperature management. Neuro- and interventional radiologists may make some significant future applications of these ideas. Of immediate practical interest is the possibility of influencing the well-being of human embryos' neural tube development in utero by a comprehensive study of their temperature environment.