ABSTRACT
In the period of development, ranging from approximately stage 28 to approximately stage 40, the yolky material is consumed, the fibre tracts and later the commissures develop, and the segregation of the various brain structures continues. A chiasmatic ridge develops as a thickening of the floor of the forebrain at stage 29/30. It is rostrally separated from the thick lamina terminalis by a shallow groove. During this period of development the brain acquires more and more its general form and structure. The anlage is relatively large, semicircular in form and contains a large lumen in broad communication with the ventricle of the brain at stage 29/30. At stage 41 the anlage of the pia mater becomes visible at the level of the mesencephalon. At stage 42 the dura-endocranial membrane begins to differentiate also at the level of the mesencephalon. At stage 43 the dura-endocranial membrane, which develops further, becomes heavily pigmented dorsal to the brain.
