2. Objective
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› Define gastrulation
› Discuss the formation of primitive streak
› Describe the formation of notochord
› Discuss the process of neurulation
3. Gastrulation
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› The formation of trilaminar disc, which composed of three
germinal layers is called gastrulation.
› It begins from the first week with the appearance of hypoblast
and then the formation of the epiblast cells.
4. Primitive Streak
› The formation of linear band of Epiblast at the
beginning of 3rd week is called as primitive streak
› On the dorsal aspect of the embryonic disc at
caudal end in midline.
› It is formed by the accumulation of epiblast cells
and migration to the center of the embryonic disc.
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12. Notochordal Process
› The primitive node from the primitive
streak, mesenchymal cells proliferates
under the ectoderm (epiblast cells) in
median plane.
› These cells forming the cellular cord
called as notochordal process.
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15. 15
Cranially the process reaches up
to prochordal plate, at plate the ecto
and endoderm fuses to form
(buccopharyngeal membrane)
Caudal to the primitive streak the
circular area , the ecto and
endoderm fuses and forming cloacal
membrane
