The following paper consists of further instalments of a research which has been conducted by the author for several years and which deals with the general pathology of mental disease from both clinical and pathological standpoints. The essential bases of a scientific general classification of mental diseases are a morbid anatomy and a general pathology. Before the latter problem could be successfully attacked a prolonged study of the structure and mode of development of the cell-layers of the cortex was necessary. This was commenced by a lengthy investigation of the region of the cortex concerned with the special sense of vision, and a paper on this subject was published in 1900.(1) This paper dealt, by the method of micrometric examination, with the general histology of the regions of the cortex cerebri concerned in the immediate reception (projection centre) and the elaboration (lower associational centre) of visual impressions; and the research resulted in the exact localisation of the primary visual area of the cerebral cortex. This region was described by the author as the “visuo-sensory” area, and to the surrounding area of visual association he applied the term “visuo-psychic.(2) The results obtained from this study of the cortical areas concerned with one special sense were considered sufficient for the purposes of the research, and the region of the cortex cerebri which occupies a higher plane in the hierarchy of cerebral function than those concerned with sensory reception and elaboration was then taken into consideration. Before, however, it was possible to apply the same method to the region of the cortex cerebri concerned in higher association and the general orderly co-ordination of psychic processes, it was first necessary to satisfactorily determine the particular part of the cortex which possesses these functions, as this is the subject of grave dispute on the part of different authors.(3)