There has recently been an attempt to recognize a pithecoid character, or atavism, in microcephalic men, the smallness of whose heads is allied with a greater or less degree of idiocy. A pithecoid structure of the brain has also been traced in several individuals who are not microcephalous, but subject to pathological affections. We will first consider those who belong to the latter category. Krause examined the brain of an ape-like boy aged seven years and a half, which, as the author remarks, approximated in structure to the pithecoid type, although without displaying microcephalic characteristics. The two cerebral hemispheres were wanting in symmetry; they diverged from each other in the region where the parieto-occipital fissure occurs on the left cerebral hemisphere, and they formed an edge which curved outward and backward so that the cerebellum remained uncovered. On the lower surface of the frontal lobes there was a strongly marked ethmoidal prominence. Neither of the fissures of Sylvius were closed, the left less so than the right; the operculum was only slightly developed; and the island of Reil and its fissures were almost uncovered. This formation is almost the same as that of the brain of anthropoids. The two central fissures of Rolando were close together, or less deeply impressed on the edge of the hemispheres than is normally the case, and forming no joint angle. Large and deeply marked pre-central fissures seemed to represent the central fissures. The intra-parietal fissures, diverging outwardly further than in man, received the parieto-occipital fissure, a structure in conformity with the typical brain of apes. The transverse occipital fissure became in this case a deep fissure like the simian fissure, crossing the occipital lobes, and almost completely dividing them from the parietal lobes. The so-called _Fissura calcarina_, to which we have referred above, had its origin on the upper surface of the occipital lobe, then joined the parieto-occipital fissure, and went directly into the hippocampal fissure (_Fissura hippocampi_) on its right side. This abnormal structure is also in conformity with the typical brain of apes. The first occipital convolution is divided from the upper parietal lobes by the parieto-occipital fissure. Gratiolet asserts that this formation occurs in many species of apes. The upper temporal convolution was remarkably reduced on both sides, possessing only an average width of 5 mm. This characteristic reminded Krause of the brain of the chimpanzee. In that animal the upper temporal convolution is always reduced. Krause therefore asks whether some human brains may not possess the typical structure of apes without being microcephalic. The brain we have described scarcely differed from the normal weight; it possessed all the convolutions and fissures, and indeed, the convolutions were perhaps more numerous than in the normal structure, yet it was