. Elements of physiological psychology; a treatise of the activities and nature of the mind, from the physical and experimental points of view . n into lobes is somewhatartificial. There is no break in the cortex between one lobe andthe next; for the cortex extends down the sides of the boundaryfissures, and continuously around the bottom of the fissures intothe adjoining lobes. Within the Sylvian fissure, the cortex ex-pands into a considerable area, cut up by smaller fissures; and this PRINCIPAL DIVISIONS OF THE CORTEX 221 concealed part of the cortex is known as the island of Reil, or,more
. Elements of physiological psychology; a treatise of the activities and nature of the mind, from the physical and experimental points of view . n into lobes is somewhatartificial. There is no break in the cortex between one lobe andthe next; for the cortex extends down the sides of the boundaryfissures, and continuously around the bottom of the fissures intothe adjoining lobes. Within the Sylvian fissure, the cortex ex-pands into a considerable area, cut up by smaller fissures; and this PRINCIPAL DIVISIONS OF THE CORTEX 221 concealed part of the cortex is known as the island of Reil, or,more briefly, as the Island. Besides the fissures which have been chosen as the grand bound-aries between the lobes, many other fissures—in the superficial man-ner above indicated—divide the lobes into smaller parts known asconvolutions or gyres. Some of these smaller fissures are incon-stant, when one individual brain is compared with another; butcertain of the more important are fairly constant, and so form ap- Central fissure Supramarginal gyre Angular ffyre Superior frontal^gyre Middle frontal gyre Precentral gyre Inferior frontal gyre. Inferiorteniporalgyre Fieaure of Sylvius Fia. 95.—Lateral Surface of the Left Cerebral Hemisphere. (Edinger.) propriate landmarks on the surfaces of the cortex. Those of mostinterest are the following: In the central region (see Fig. 95),or that immediately adjacent to the central fissure, we may dis-tinguish two gyres, one on each side of the central fissure, and ex-tending along it; they are separated from the rest of the frontaland parietal lobes, respectively, by the precentral and postcentralfissures. These gyres are named the precentral and the the front of the precentral fissure lies the great extent of the frontallobe, which is partially divided into superior, middle, and inferiorgyres by two horizontal fissures, called the superior and the infe-rior frontal. In the temporal lobe, also, there is a series of hori-zonta
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