When a young doctor at the Asylum in Pavia, he was requested to make a post-mortem examination on a criminal named Vilella, an Italian Jack the Ripper, who by atrocious crimes had spread terror in the Province of Lombardy. Scarcely had he laid open the skull, when he perceived at the base, on the spot where the internal occipital crest or ridge is found in normal individuals, a small hollow, which he called _median occipital fossa_ (see Fig. 1). This abnormal character was correlated to a still greater anomaly in the cerebellum, the hypertrophy of the vermis, _i.e._, the spinal cord which separates the cerebellar lobes lying underneath the cerebral hemispheres. This vermis was so enlarged in the case of Vilella, that it almost formed a small, intermediate cerebellum like that found in the lower types of apes, rodents, and birds. This anomaly is very rare among inferior races, with the exception of the South American Indian tribe of the Aymaras of Bolivia and Peru, in whom it is not infrequently found (40%). It is seldom met with in the insane or other degenerates, but later investigations have shown it to be prevalent in criminals. This discovery was like a flash of light. "At the sight of that skull," says my father, "I seemed to see all at once, standing out clearly illumined as in a vast plain under a flaming sky, the problem of the nature of the criminal, who reproduces in civilised times characteristics, not only of primitive savages, but of still lower types as far back as the carnivora." =FIG. 1 FOSSETTE OCCIPITAL (see page 6)= Thus was explained the origin of the enormous jaws, strong canines, prominent zygomæ, and strongly developed orbital arches which he had so frequently remarked in criminals, for these peculiarities are common to carnivores and savages, who tear and devour raw flesh. Thus also it was easy to understand why the span of the arms in criminals so often exceeds the height, for this is a characteristic of apes, whose fore-limbs are used in walking and climbing. The other anomalies exhibited by criminals--the scanty beard as opposed to the general hairiness of the body, prehensile foot, diminished number of lines in the palm of the hand, cheek-pouches, enormous development of the middle incisors and frequent absence of the lateral ones, flattened nose and angular or sugar-loaf form of the skull, common to criminals and apes; the excessive size of the orbits, which, combined with the hooked nose, so often imparts to criminals the aspect of birds of prey, the projection of the lower part of the face and jaws (prognathism) found in negroes and animals, and supernumerary teeth (amounting in some cases to a double row as in snakes) and cranial bones (epactal bone as in the Peruvian Indians): all these characteristics pointed to one conclusion, the atavistic origin of the criminal, who reproduces physical, psychic, and functional qualities of remote ancestors.