At four (4) weeks of gestational development, the neural crest cells (the precursors of the nose) begin their caudad Migration.

http://en.wikipedia.org/wiki/Anatomy_of_the_human_nose

At four (4) weeks of gestational development, the neural crest cells (the precursors of the nose) begin their caudad migration (from the posterior) towards the midface. Two symmetrical nasal placodes (the future olfactory epithelium) develop inferiorly, which the nasal pits then divide into the medial and the lateral nasal processes (the future upper lip and nose).