Henry Gray (18251861). Anatomy of the Human Body. 1918.
in the adult brain are represented by the lateral root of the olfactory tract and the uncus. The position and connections of the remaining portions of the rhinencephalon are described with the anatomy of the brain.
The corpus striatum (Figs. 651 and 653) appears in the fourth week as a triangular thickening of the floor of the telencephalon between the optic recess and the interventricular foramen, and continuous behind with the thalamic part of the diencephalon. It increases in size, and by the second month is seen as a swelling in the floor of the future lateral ventricle; this swelling reaches as far as the posterior end of the primitive hemisphere, and when this part of the hemisphere grows backward and downward to form the temporal lobe, the posterior part of the corpus striatum is carried into the roof of the inferior horn of the ventricle, where it is seen as the tail of the caudate nucleus in the adult brain. During the fourth and fifth months the corpus striatum becomes incompletely subdivided by the fibers of the internal capsule into two masses, an inner, the caudate nucleus, and an outer, the lentiform nucleus. In front, the corpus striatum is continuous with the anterior perforated substance; laterally it is confluent for a time with that portion of the wall of the vesicle which is developed into the insula, but this continuity is subsequently interrupted by the fibers of the external capsule.
FIG. 656 Diagrammatic coronal section of brain to show relations of neopallium. (After His.) Cs. Corpus striatum. Th. Thalamus. (See enlarged image)
The neopallium(Fig. 656) forms the remaining, and by far the greater, part of the cerebral hemisphere. It consists, at an early stage, of a relatively large, more or less hemispherical cavitythe primitive lateral ventricleenclosed by a thin wall from which the cortex of the hemisphere is developed. The vesicle expands in all directions, but more especially upward and backward, so that by the third month the hemispheres cover the diencephalon, by the sixth they overlap the mid-brain, and by the eighth the hind-brain.
The median lamina uniting the two hemispheres does not share in their expansion, and thus the hemispheres are separated by a deep cleft, the forerunner of the longitudinal fissure, and this cleft is occupied by a septum of mesodermal tissue which constitutes the primitive falx cerebri. Coincidently with the expansion of the vesicle, its cavity is drawn out into three prolongations which represent