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Carnegie Stage 17 Introduction

Stage 17 embryos have a greatest length of 11 to 14 mm and an estimated post-fertilization age of 41 days. Hand rays have formed and the auricular hillocks are distinct. The stage is represented by Carnegie embryo #6520 that had a grade of excellent but was more recently downgraded to good. It is still considered to be one of the best specimens in the Carnegie collection at this stage. It has a corrected greatest length of 14.2 mm (after fixation). The specimen is considered to be median within the stage.

The embryo was fixed in corrosive acetic acid, embedded in celloidin and paraffin and serially sectioned transverse to the long axis at 10 microns. The sections were mounted on 72 large glass slides and stained with alum cochineal (i.e., carmine). Silver was added later to slides 1 thru 25. There are 1073 sections through the embryo. Every other section was digitally captured. The Browse part of the database includes 186 of the 1073 sections. Approximately every seventh section was digitally restored and labeled, and can be viewed at four magnifications.

Several 3D reconstructions were produced from the aligned section images. Animations of the 3D reconstructions and flythrough animations of the aligned section images are also included on the disk.

Images, including a photograph of the right side of the embryo before it was sectioned and multiple reconstructions, were included in O'Rahilly and Müller Developmental Stages in Human Embryos.

Source: The Virtual Human Embryo.