The present paper describes a procedure for unfolding and flattening gyrencephalic brains that makes it possible to cut single tangential sections through extensive regions of originally convoluted cortex. This procedure involves incising the arachnoid, removing the white matter, and then opening up the gyri and sulci in tissue that has been fixed in such a way as to maintain much of its natural flexibility. A technique is also described for preserving the complete gyral pattern of the intact brain on the surface of a flattened cerebral hemisphere. Finally, examples are presented in which the gyral pattern in the cat brain is related to the location of identified cortical areas in myelin-stained tangential sections from flattened material.