. Anatomischer Anzeiger. Anatomy, Comparative; Anatomy, Comparative. 423 surface of the cerebellum from behind, for in this stage of development the greater part of the cerebellum lies intraventricular. The first in- dication of this state is to be found in a model of His ^), representing the cerebrum of an embryo with a rump-vertex-length of 53 mm. In this model the cerebellum shows on each side of the median plane a prominence into the fourth ventricle. Now, in the stage of develop- ment, shown in the embryo of 55 mm these prominences have con- siderably increased. As a consequence of this i
. Anatomischer Anzeiger. Anatomy, Comparative; Anatomy, Comparative. 423 surface of the cerebellum from behind, for in this stage of development the greater part of the cerebellum lies intraventricular. The first in- dication of this state is to be found in a model of His ^), representing the cerebrum of an embryo with a rump-vertex-length of 53 mm. In this model the cerebellum shows on each side of the median plane a prominence into the fourth ventricle. Now, in the stage of develop- ment, shown in the embryo of 55 mm these prominences have con- siderably increased. As a consequence of this increment in size they meet in the median plane forming a rafe (Fig. 1 B). 1 should be in- clined to believe, led by the histiological structure of the top of the rafe (Fig. 5), that the two prominences unite in this rafe, thus pro- ducing an increase in thickness of the median zone of the cerebellum. The primitive part of this zone may be re- cognized by the fact that it comprises the dorsal commissure of the cerebellum (Fig. 1 ). By this large intra- ventricular prominence the form of the lamina cerebelH has changed. If we disregard for a moment the tela cho- rioidea, the cerebellum as seen from the side, is triangular. The superior surface, which is the uncovered one, goes over into the postero-inferior surface. At the place of passage we find the insertion of the tela chorioidea, so that the whole postero-inferior surface is covered by the superior sheet of the tela chorioidea. This state was first described by His and afterwards by Bolk. The angle at which. Fig. 2. Frontal section at a distance of mm from the posterior border of the cerebellum. 15/1. Out- line of a photograph. brachium conjunctivum. C. cerebellum. Isth. isthmus. 3Ies. mesencephalon. fissura chorioidea. plica encephali dorsalis. T. taenia. tela chorioidea of the fourth ven- tricle. valvula cerebelli. mesencephalic ven- tricle. fourth ventricle. 1) W. His
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