I. Introduction.- II. Material and Methods.- A. Animals. Histological Methods.- B. Graphic Reconstructions.- C. Nomenclature.- III. Observations.- A. Parahippocampal Areas except Area Entorhinalis.- 1. Cytoarchitectonics.- 2. Sulphide Silver Pattern.- a) Presubiculum.- b) Area 29e.- c) Parasubiculum.- B. Area Entorhinalis and its Transition to the Pyriform Cortex and the Amygdala.- 1. Cytoarchitectonics.- a) Medial Part, Area 28M.- b) Lateral Part, Area 28L.- c) Transition between Medial and Lateral Parts of Area 28.- d) Definition of a New Ventromedial Part, Area 28M'.- e) "Transitional" Area, TR, between Areas 28, 51 and the Amygdala.- f) Definition of a New Ventrolateral Part, Area 28L'.- 2. Sulphide Silver Pattern.- a) Medial Part, Area 28M.- b) Lateral Part, Area 28L.- c) Transition between Medial and Lateral Parts.- d) Ventrolateral Part, Area 28L'.- e) Ventromedial Part, Area 28M'.- f) Transition Area, TR.- IV. Discussion.- A. Regional and Laminar Subdivision.- 1. Parahippocampal Areas except Area Entorhinalis.- a) Presubiculum.- b) Area 29e.- c) Parasubiculum.- 2. Area Entorhinalis and its Transition to the Pyriform Cortex and the Amygdala.- a) Areas 28M and 28L.- b) Areas 28M', 28L' and TR.- c) Comment on Area Perirhinalis.- d) Concluding Remarks on Entorhinal Subareas.- B. Are the Sulphide Silver Stainable Structures and Substances Identical to Previously Identified Tissue Components'.- V. Summary.- Appendix: Review of Previous Subdivisions of the Entorhinal Area.- References.- Figures1-49.