Skip Navigation

Carnegie Stage 11 Introduction

Stage 11 embryos have a greatest length of 1.4 to 5 mm and an estimated postfertilization age of 28 to 30 days. There are 13 to 20 pairs of somites or body segments along the body axis. Sclerotomes are forming in the ventromedial part of the somites as the somite remnants move dorsolatterally. The rostral neuropore closes and the optic vesicle forms at the outer part of the optic sulcus in the wall of the diencephalon. The otic placode or pit is present as thickened ectoderm lateral to the rhombencephalon. The adenohypophyseal primordium is forming just rostral to the oropharyngeal membrane that is beginning to disappear. The ectodermal ring is present but interrupted as thickened ectoderm on the lateral surface of the embryo. Right and left horns of the sinus venosus are continuous with their respective atrium. The hepatocystic diverticulum can be identified in the endoderm at the fore- mid-gut junction. Mesonephric vesicles and duct appear in the nephrogenic cord.

The stage is represented by Carnegie embryo #6344 that has a grade of excellent. It was selected for digital replication because it is one of the best transversely sectioned specimens at this stage in the collection. The age of the embryo is estimated to be 28 postfertiliation days, which places it in the early part of the stage. It has a greatest length of 2.5 mm (after fixation) and there are 13 pairs of somites along the body axis. Dr. B.S. Kline collected the specimen in April 1931. The embryo was fixed and transferred to the Carnegie Institution of Embryology in 10% formalin. It was embedded in 8% celloidin and paraffin and serially sectioned transverse to the long axis at 6 microns. The 575 sections were mounted on six large glass slides (click for images) and stained with alum cochineal (i.e., carmine). There are 407 sections through the embryo.

The database contains 137 section images of the sections. Approximately every third 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 of the embryo's surface and the internal anatomy together with fly-through animations of the aligned section images are also included on the disks.

The morphology of this embryo is well documented in the literature. The Carnegie collection contains photographs of the embryo before it was sectioned and reconstructions.

Source: The Virtual Human Embryo.