The somites develop from the segmentation of the paraaxial mesoderma, that is next to the neural tube. The segmentation leads to formation of individual blocks that each consist of a mesenchymal hollow space (somitocelum) that is covered with epithelial tissue.
In the course of further development, the somite differentiates into three parts:
The neural crest is an embryionic tissue structure which develops during neurulation between the neural tube and the superficial ectoderm. The neural tube is a tissue structure which develops when the neural folds meet and coalesce in the middle.(25th day) Development of the neural tubeThe neural tube is the result of the so called neurulation and is the precursor structure of the nervous system. It develops in two stages:During the primary neurultion, the lateral edges of the neural plate fuse together to form a neural groove. It ends with the closure of the posterior neuropore at the end of the fourth week.During the secondary neurulation the neural tube deepens inside of the embryo to form a hollow space. This stage comes directly after the primary neurulation and ends in the sixth week.
