Whilst pursuing certain investigations upon the comparative histology of the brain, the authors of this article have been enabled to demonstrate certain facts with regard to cortical lamination, and to show the disposition and significance of certain elementary constituents, the importance of which, they believe, justifies their publication. Meynert enumerates five distinct plans, according to which the various layers of the cortex are disposed, of which the more extensive formation is his five-laminated type, which he regards as that characteristic of the cortex of the vault and a portion of the gyrus fornicatus. It is with regard to this type of structural lamination that the observations now to be recorded d eal; and it is hoped that they will tend not only to point out how errors have crept into the descriptions of some writers, but also to reconcile conflicting opinions upon this subject. We regard the ascending frontal convolution as affording the most suitable representation of the typical lamination of the motor area, and our descriptions, therefore, apply more directly to this region than to the remaining gyri at the vertex.