Smallness of the cranium is one of the commonest findings in severe mental defect. Ashby and Stuart (1933 and 1934) found a correlation between brain weight and mental age of +0.15, but they regarded this as part of the more general positive correlation of +0.24 which they observed between body weight and mental age. In discussing this subject elsewhere (Hilliard and Kirman, 1957), Crome and Kirman have taken a more definite stand on this matter in so far as idiocy and imbecility are concerned and regard reduced brain weight, which is so often associated with a small cranium, as one of the major factors in reduced intelligence. Crome (1957) found marked reduction in size to be the commonest abnormality in brains of low-grade defectives.