For a comprehensive background in Embryology look at the UNSW Embryo Program available on the Web. Note the still large ventricular space and that the brain has only just begun to develop at this late embryonic stage. Most growth occuring late fetal and post-natally. In comparison, the spinal cord looks similar to its mature form. 4th ventricle- ventricular cavity within the rhombencephalon .
Space is continuous with ventricular system of the brain.
Connects centrally with the dorsal horn of the spinal cord. Generated from neuroepithelial stem cells in ventricular zone of neural tube. Form astrocytes, oligodendrocytes. In the brain it is the outer layer, in the spinal cord it is inner layer. Expression of different Hox genes along neural tube defines rostral-caudal axis and segmental levels.