The superior temporal, the middle temporal and the inferior temporal gyri are of nearly equal width (Figs. 28 and 31). They fuse with one another and with the fusiform gyrus at the temporal pole, when anterior temporal sulcus is absent. The superior temporal gyrus is continuous with the supramarginal and angular gyri, posteriorly: in its third and fourth fifths and in the transverse temporal gyri is the receptive auditory center (Barker).
The middle temporal gyrus fuses at its posterior end with the angular gyrus and either with the post-parietal or the superior occipital. Along the superior temporal sulcus, in the middle two-fourths of the superior and middle temporal gyri is the center for auditory memories, the psychic auditory center.
This center is in the left hemisphere of right-handed people (Figs. 74 and 76).
The inferior temporal gyms forms the infero-lateral border of the hemisphere (Figs. 28 and 31). It is continuous with the lateral occipital gyrus and sometimes, also, with the superior occipital and post-parietal gyri. If this gyrus and the lower half of the middle temporal gyrus be divided into four equal parts, each fourth, according to Mills, belongs to a definite center. From behind forward they are the center of orienta tion; the center of equilibration (?); the naming center; and, in the anterior fourth and the pole of the temporal lobe, the center of intonation (Fig. 76).
5. The island (insula, Reili) is also called the central lobe (Figs. 3o, 31, 38 and 47). It is situated in the medial wall of the lateral fissure of the cerebrum, between the frontal, parietal and temporal lobes, whose growth, after the fifth month in utero, gradually covers it over. At the end of the first year of extrauterine life it is entirely concealed by temporal, parietal, and frontal parts of the operculum. The island is thus sepa rated from the general surface of the cerebral hemisphere by a distance of half or three-quarters of an inch. It is triangular in shape. Its apex is directed downward and forward toward the fossa lateralis cerebri, and is called the pole (poles insulce). If the lips of the lateral fissure be widely separated, the sulcus circularis insulin may be seen separating the island from the frontal, parietal and temporal lobes (Figs. 3o, 31 and 47). The circular sulcus is lacking only at the antero-inferior part, at the pole, where the cortex of the island is continuous with that of the posterior orbital gyrus and with the anterior per forated substance, and is on the same level as the orbital area of the basal surface. The imaginary line separating the an
terior perforated substance from the island is called the threshold of the island (limen insulce).
In the island there is one named sulcus and four to six gyri which have a. radial or fan-like grouping (Fig. 25): Sulcus { Central of the island (s. centralis insulin).
Gyri f Short (gyri breves), three or four of them. 1 Long (gyrus longus—furcalis).
The sulcus centralis insulce begins at the apex, or pole, of the island and runs obliquely upward and backward dividing the lobe into two lobules (Fig. 3o). It is in the same transverse plane as the central sulcus (of Rolando). In front of it, is the precentral lobule composed of the short gyri and continuous with the frontal lobe; the lobule lies behind it and is in continuity with the parietal, temporal and limbic lobes.
The gyri breves inuslx, three or four in number, are separated by shallow furrows which diverge upward and backward from the smooth apex of the precentral lobule (Fig. 3o). They are joined to the orbital operculum by a short annectant gyrus (gyrus transverses insulce of Eberstaller) which extends from the apex around the lower end of the anterior circular sulcus. Their connection under the circular sulcus with the foot of the in ferior frontal gyrus suggests a participation in the speech center, and they are figured by Mills in that center. However, the paraphasia which results from lesions in the short gyri may be due to the involvement of an association tract of fibers running underneath them.
Gyrus Longus (Furcalis) (Fig. 30).—It lies behind the central sulcus of the island and trends obliquely backward and upward. Posteriorly, it bifurcates for a short distance forming two short branches which are continuous under the circular sulcus with the parietal lobe; it fuses with the temporal lobe and the gyrus hippocampi of the limbic lobe, inferiorly.
The olfactory lobe and the limbic lobe, comprising the rhinen cephalon and a part of the neopallium, also belong to the cerebral hemisphere; but no part of either can be seen on the convex surface (Figs. i8, 21 and 34),