The data we have concerning the behavior of children born, living, without head or without brain, and of microcephalous children, as well as of idiots and cretins more advanced in age, are of great interest, as helping us to a knowledge of the dependence of the first psychical processes upon the development of the brain, especially of the cerebral cortex. Unfortunately, these data are scanty and scattered. Very important, too, for psychogenesis, are reports concerning the physiological condition and activity of children whose mental development has seemed to be stopped for months, or to be made considerably slower, or to be unusually hastened. Scanty as are the notes I have met with on this matter, after much search, yet I collect and present some of them, in the hope that they will incite to more abundant and more careful observation in the future than has been made up to this time. A good many data concerning the behavior of cretin children are to be found in the very painstaking book, "Neue Untersuchungen ueber den Kretinismus oder die Entartung des Menschen in ihren verschiedenen Graden und Formen" ("New Investigations concerning Cretinism, or Human Deterioration, in its Various Forms and Degrees"), by Maffei and Roesch (two vols, Erlangen, 1844). But, in order that these data should be of value, the observed anomalies and defects of the cerebral functions ought to be capable of being referred to careful morphological investigations of the cretin brain. As the authors give no results of _post-mortem_ examinations, I simply refer to their work here.