13 pairs of somites are formed.

Lengthening of foregut and sub cephalic pocket.

Hindgut appears as the cavity of the tail fold.

Development of neural tube and neural pore. A rhomboid like depression called sinus rhomboidatis is seen.

Anterior region of the neural tube has begun to expand into 3 brain region.

Optic vesicles develop as a pair of evagination from the lateral wall of prosencephalon.

Neural crest cells are formed.

Development of heart.

Outer limit of area vasculosa development into sinus terminalis, a circular blood vessel.