<prompt> Which of the following is present at the beginning of 3rd week?NotochordPrimitive streakMesodermNeural crest cells  <response>: Primitive streak appears at the end of the 2nd week of intrauterine life and beginning of 3rd week, epiblast cells in the primitive streak forms the notochord, mesoderm and neural crest cells later in the third week. Disc with three germ layers are formed at 3rd week of gestation. Ref: Grays 39ep-210-220 