File:Stage9sm.jpg

Carnegie Stages 9

Features: embryonic disc, primitive node, primative streak, primative groove, somites, neural groove, brain plate region, connecting stalk, cut edge of amnion

Facts: Week 3, 19 - 21 days, 1.5 - 2.5 mm, Somite Number 1 - 3

View 1: embryonic disc, showing the epiblast viewed from the amniotic (dorsal) side.

Events: Ectoderm - Neural plate brain region continues to expand, neural plate begins folding over the notochord. Mesoderm - segmentation of paraxial mesoderm begins (1 - 3 somite pairs), cardiac primordium forms

Identify: neural groove and neural folds, the mesoderm, which segments beside the neural groove to form somites but extends laterally to margin of embryonic disc lateral plate mesoderm, where it merges with the covering extraembryonic mesoderm.

The intra-embryonic coelom develops in the middle of the lateral plate mesoderm. Note amniotic ectoderm covered by extramebryonic mesoderm (empty spaces above and below the mesoderm are artefacts, as are the lateral folds in the ectoderm).

Original file name: CSt9b.gif

Image Source: UNSW Embryology, no reproduction without permission. UNSW Embryology Carnegie Stage 9