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Carnegie Stage 10 - First Trimester
Neural Folds
Heart Folds Begin to Fuse


SIZE: 1.5 - 3.0 mm

TIME PERIOD: 21- 23 days post-ovulation

Rapid cellular growth and change elongates the embryo and expands the yolk sac.

On each side of the
neural tube, between four and twelve pairs of somites can exist by the end of Stage 10. The cells which become the eyes appear as thickened circles just off of the neural folds. The newly differentiated cells of the ears are also present.

Neural folds are rising and fusing at several points along the length of the neural tube concomitant with the budding somites which appear to "zipper" the neural tube closed. Neural crest cells will eventually contribute to the skull and face of the embryo.

The two
endocardial tubes formed in Stage 9 now fuse in Stage 10. Together they form one single tube generated from the cells of the "roof" of the nueral tube. The heart tube takes on an S-shape establishing the asymetry of the heart. As the S-shape forms, cardiac muscle contraction begins.

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