Gastrulation and Primitive Streak

During the third week of embryonic development, which of the following structures is formed by the epiblast?

During gastrulation, epiblastic cells migrate through the primitive streak to form the three primary germ layers. Which of the following is the most common fate of cells that ingress through the cranial (anterior) end of the primitive streak?

A 32-year-old woman at 20 weeks gestation undergoes routine anatomy scan. The sonographer identifies a midline mass in the lumbosacral region with both cystic and solid components. There is no associated spinal dysraphism. The radiologist notes the mass is intimately related to the coccyx and sacrum. Based on the embryological origin from the primitive streak and caudal eminence, what is the most appropriate next step in management?

During gastrulation, epiblast cells migrate through the primitive streak to form the three primary germ layers. Which of the following is the most common cell type that ingresses through the primitive streak to form the embryonic mesoderm?

Which feature best distinguishes the primitive streak from the primitive node (Hensen's node equivalent) during human gastrulation?