No natural endocast was found with the cranial remains of Zinjanthropus. However, so much of the endocranial surface of the calvaria was preserved as to make possible the preparation of a plaster endocast (pl. 28). This was effected by me, with the invaluable expert assistance of Messrs A. R. Hughes and T. W. Kaufman of the staff of the Department of Anatomy, University of the Witwatersrand. Approximately the posterior twothirds of the brain-case was virtually complete; likewise, the frontal poles and rostral regions. The area between had to be reconstructed. There is little doubt as to the intervening distance, because of a satisfactory approximation between the anterior and posterior calvarial parts. On the basis cranii, the gap includes the anterior part of the middle cranial fossa and most of the anterior cranial fossa; thus, the precise extent of the temporal lobes and the exact position of the temporal poles could not be determined from the surviving cranial bones. A guide to these points is provided by the body of the sphenoid, most of which is present as far forward as the posterior half or more of the hypophyseal fossa on its dorsum, while ventrally a substantial part of the vomer articulates with the sphenoidal rostrum. In higher Primates, the medial aspect of the temporal poles abuts close to the body of the sphenoid.