• The notochordal process develops by the migration of mesenchymal cells cranially from the primitive node, eventually stopping at the bucco-pharyngeal membrane (a bilayer disk of endoderm/ectoderm)
• The floor of the notochordal process fuses with the intra-embryonic endoderm of the yolk sac
• The fused layers degenerate temporarily to form a transitory communication with the yolk sac (neurenteric canal)

• The notochordal plate folds inward, to form a rod-shaped notochord; cell proliferation occurs cranially to caudally
• As the notochord closes as a tube, it detaches from the endoderm of the yolk sac
• It is now located in the mesoderm, between the endoderm and ectoderm

Functions of the Notochord:
1. Structure - acts as a rigid axis around which the embryo develops
2. Skeletal - foundation upon which the vertebral column (vertebral bodies) will form
*3. Induction - will bring about formation of the neural tube (future nervous system)*

Fate of notochord: It will eventually break up into section of weight-bearing intervertebral disks, known as the nucleus pulposos (this little structure may give rise to what is commonly known as a "slipped disk." For a foretaste of Unit 5, click here). A tumor can occur here, known as a chordoma, localized in the intervertebral disk, capable of causing nerve damage.

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