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Carnegie Stage 7 Introduction

Stage 7 embryos are in the presomite period with a well-defined embryonic disc. They have an estimated postfertilization age of approximately 18 to 21 days and a greatest length of 0.6 mm. The embryonic disc is symmetrical and slightly convex in the plane of its longitudinal axis. The gastrulation (primitive) node and notochordal process can be identified.

The stage is represented in the database by Carnegie embryo #7802 that had been given a grade of excellent. This specimen has a few characteristics of stage 8 embryos and is therefore considered as an advanced stage 7. It measures 0.42 mm in length, 0.35 mm in maximum width, and about 0.05 mm in maximum thickness. The specimen was collected and prepared for microscopic examination in 1940. It was fixed in 70% alcohol and then in Bouin's fluid, embedded in celloidin / paraffin, and serially sectioned transverse to the longitudinal axis at 6 microns. The sections were mounted on glass slides and stained with hematoxylin and eosin. The 100 sections through the embryonic disc and closely adjacent tissue are located on slides 41 to 46. Structures are labeled on every section image.

The morphology of this embryo is well documented in the literature. There are photographs of the implantation site and graphic reconstructions of the specimen. A drawing through the median plane showing the right half of the embryo was made from a model by Mr. J.F. Didusch in 1944. We have generated a digital reconstruction of the median longitudinal section corresponding to this drawing.

The sections have been digitally restored and labeled, and can be viewed at three magnifications. Several 3D reconstructions have been produced from the aligned sections. Labeled and unlabeled animations of the 3D-reconstructions together with fly-through animations of the aligned sections are also included on the disk.


Source: The Virtual Human Embryo.