Those who seek for the source of the arrested or perverted brain development in the reaction of an abnormally growing and ossifying skull on the skull contents are in error. The premature ossification theory does not hold good even for the microcephali; it is to be doubted if it ever had any justification in view of the often open character of the sutures. Taking the well-studied cases of asymmetry, the variability of a single factor shows that caution is needed in referring cerebral anomalies to any single influence. In Muhr's case (cited by Spitzka) the atrophic cerebellar hemisphere was on the same side with the atrophic cerebral hemisphere. The internal carotid artery of that side was of lesser calibre and the entire skull half shortened. Here the lagging behind in growth of one half of the skull appears on first sight to explain the retarded development of the corresponding halves of the cerebrum and cerebellum. In view of the atypy of the gyri, however, an atypy not to be explained purely on mechanical grounds, it is more reasonable to believe that the imperfect development of certain vascular channels was either concomitant or secondary to a primitive anomaly of the cerebral hemisphere. The retarded skull growth would have to be looked upon as a tertiary occurrence and the cerebellar defect as a final ensuing result. Ordinarily with defective development of one cerebral hemisphere the cerebellar defect is on the opposite side, herein following the course of the anatomical connections of that development and of the secondary degenerations. The deviation from this rule in Muhr's case was due to the entering of the abnormal skull-shape, itself secondary to other defects, as an element influencing brain growth at a special period of development. An abnormal shape of the skull, generally associated with a cerebral defect, and hence valuable as a physical sign presumably indicating mental anomalies, may exert an important modifying influence at a late period on the contained brain, but the grosser defects in the cerebral architecture must antedate the period of skull growth and be deeply planted as an original intrinsic fault in the brain blastema itself. The researches of His have shown how important for the definitive shape of the body and its organs are the position of individual cells, the portion of the germ area, the convexity and length of germ curves and the relative rate of growth of different germ areas. And as the experiments of other embryologists have established the possibility of producing monstrosities analogous to cerebral defects by altering the conditions ever so slightly, the general conclusion follows that the fundamental error of development at the foundation of malformations associated with degeneracy is to be located at a very early period of embryonic, or possibly of ovuline life. Certain of these anomalies are due to a disturbance of the balance between the