Archive image from page 412 of The development of the human. The development of the human body : a manual of human embryology . developmentofhum00mcmu Year: 1914 THE TELENCEPHALON 401 it forms the roof of the interventricular foramen, is prolonged out upon the dorsal surface of each hemisphere, and, becoming invag- inated, forms upon it a groove.' As the hemispheres, increasing in height, develop a mesial wall, the groove, which is the so-called chorioidal fissure, comes to lie along the ventral edge of this wall, and as the growth of the hemispheres continues it becomes more and more elongat
Archive image from page 412 of The development of the human. The development of the human body : a manual of human embryology . developmentofhum00mcmu Year: 1914 THE TELENCEPHALON 401 it forms the roof of the interventricular foramen, is prolonged out upon the dorsal surface of each hemisphere, and, becoming invag- inated, forms upon it a groove.' As the hemispheres, increasing in height, develop a mesial wall, the groove, which is the so-called chorioidal fissure, comes to lie along the ventral edge of this wall, and as the growth of the hemispheres continues it becomes more and more elongated, being carried at first backward (Fig. 241), then ventrally, and finally forward to end at the tip of the temporal lobe. After the establishment of the grooves the mesenchyme in their vicinity dips into them, and, developing blood-vessels, becomes the chorioid plexuses of the lateral ventricles, and at first these plexuses grow much more rapidly than the ventricles, and so fill them almost completely. Later, however, the walls of the hemispheres gain the ascendancy in rapidity of growth and the plexuses become relatively much smaller. Since the portions of the roof-plate which form the chorioidal fissures are continuous with the velum interpositum in the roofs of the interventricular foramina, the chorioid plexuses of the lateral and third ventricles become continuous also at that point. Fig. 241. -Median Longi- tudinal Section of the Brain of an Embryo Calf of 5 cm. cb, Cerebellum; cp, chorioid plexus; cs, corpus striatum; JM, interventricular foramen; in, The mode of growth of the chorioid hypophysis; m, mid-brain; oc, , optic commissure; t, posterior fissures seems to indicate the mode of part of the diencephalon — growth of the hemispheres. At first the Wihalkovicz.) growth is more or less equal in all directions, but later it becomes more extensive posteriorly, there being more room for expansion in that direction, and when further extension backward becomes diffic
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