Slide 5 of 7
Once Hensenís Node reaches the most anterior end of the embryo, it begins to retreat again, leaving behind the head process, a group of cells that will eventually form the structures of the chickís head. The last cells to pass through the streak as it recedes are destined to become the notochord
The recession of Hensenís Node marks the beginning of a new phase of development, in which structures begin to differentiate. Since Hensenís node recedes from the anterior end first, the development at the anterior end begins sooner than at the posterior end. Therefore, the anterior to posterior gradient of maturity is evident.