The present division of this paper consists of a clinical description of those types of mental disease which are classed by the writer under the heading Amentia. Under this term he includes, from the standpoint of morbid anatomy, all cases of subnormal cerebral development, and from that of clinical symptomatology, all cases of subnormal, and hence frequently abnormal, mental manifestation. He thus uses the term amentia to connote in the widest sense the mental condition of patients suffering from deficient neuronic development.