His skull is clearly, and to an extraordinary degree, brachycephalic, great in breadth and receding towards the nape of the neck without exceeding the vertical. Here is an illutration which brings to nought the old assurances of the phrenologists and certain biologists, according to which genius is the prerogative of the dolichocephales. The skull of Einstein reminds me, above all else, of that of Renan, who was also a brachycephale. As with Renan the forehead is huge; its breadth exceptional, its spherical form striking one more than its height.
Einstein: The Life and Times, by Ronald W. Clark, p. 353
See also Cranial Size and Shape and the German Hyperbrachycephals.