Talk:BGDB Gastrointestinal - Trilaminar Embryo
BGD Internal Links 2009
Carnegie stage 11 Week 4, 23 - 26 days, 2.5 - 4.5 mm, Somite Number 13 - 20
View: This is a dorsolateral view of embryo. Amniotic membrane removed.
View: Embryo cross-section through the trunk region (low power inset).
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 will develop later 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).
View: Embryo cut longitudinally (opposite orientation to first image; rostral to left, caudal right)
Since all embryos are twisted, the "longitudinal" section actually cuts obliquely through the brain and neural tube, showing where these structures open into the amniotic sac, i.e., the cranial and caudal neuropores respectively.
Identify: Somites, Embryonic Heart (cut in three places)
GIT - foregut (lying between the brain and the heart), midgut ("roof" region of the yolk sac) and hindgut.
(Note: The foregut appears to be separated from the midgut by a dense column of tissue, but this is a section through one of the umbilical veins crossing to the heart obliquely from the side of the embryo)
Transverse septum (cut in cross-section, inferior to the heart, site where liver and diaphragm arise)