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Carnegie Stage 9 Introduction

Stage 9 embryos have a greatest length of 1.4 to 2.5 mm and an estimated postfertilization age of approximately 25 to 27 days. Carnegie embryos at this stage are scarce. The somite period begins with the formation of one to three somites. The pro- mes- and rhomb- encephalon can be identified in the cephalic part of the neural folds. The pericardial cavity is present for the first time and the right and left ventricles and right and left atria can be identified by their positions. The dorsal aorta, aortic arch arteries and umbilical vessels are present. The foregut, midgut and hindgut can be distinguished for the first time and the cloacal membrane is present near the caudal part of the hindgut.

The stage is represented by Carnegie embryo #3709 that was classed as an early stage 10 because it has 4 somites. However, many of its features are consistent with stage 9, particularly the level of cardiovascular and nervous system development. It was given a grade of poor but was selected for digital replication because it is the best transversely sectioned specimen at this stage in the collection. The age of the embryo is estimated to be 25 postfertilization days and has a greatest length of 1.74 mm (after fixation). The specimen was prepared for microscopic examination in 1921, and was originally part of the collection (#H 279) housed at the University of Chicago. The embryo was fixed in formol, embedded in paraffin, and serially sectioned transverse to the long axis at 10 microns. The sections were mounted on 2 large glass slides and stained with erythrosin. There are 153 sections through the embryo.

The morphology of this embryo has been documented in the literature.

The DREM database includes all 153 of the sections. The sections have been digitally restored and labeled, and can be viewed at four magnifications. Several 3D reconstructions have been produced from the aligned sections. Animations of the 3D-reconstructions of the embryo surface and the internal anatomy together with a fly-through animations of the aligned sections are also included on the disks.

Source: The Virtual Human Embryo.