Category talk:Carnegie Stage 9

Piersol, W. H. 1937. A human embryo of two somites, in situ. Anat. Rec, 67 suppl, 39-40.

American Association of Anatomists, Fifty-Third Annual Session, University of Toronto, Toronto, Canada, March 25 to 27, 1937

(6) 88. A human embryo of two somites, in situ. W. H. Piersol, Department of Anatomy, University of Toronto.

The embryo measures 2.03 x 0.72 mm. and has been sectioned sagittally. Contact between embryonic and maternal tissue is preserved over a considerable area. although elsewhere there is separation due to shrinkage. Numerous glands form 9. broad stratum spongiosum. Flattened in the stratum compaetum, their middle parts are much dilated; toward the muscularis they are again flattened. Frequently they contain degenerated detritus and occasionally blood. A few glandular remains occur in the peripheral parts of the decidua capsularis. Chorionic villi are longest and most numerous toward the decidua marginalis. Their tips may reach the maternal tissues or a spongy mass of trophoblaet may intervene. Cytotrophoblast predominates, frequently bordered and penetrated by plasmodiotrophoblast. On the chor-ionic wall the trophoblast may show only one layer of nuclei but two layers are the rule. On the villi there are two layers of nuclei, the inner ones frequently belonging to distinct cells. The pericardial cavity is present but contains no heart, nor are their blood vessels in any part of the embryo, the chorion, or its villi. The neurenterie canal is closed but its remains are evident. An endodermal allantois projects into the connecting stalk. Small blood islands are present in the wall of the yolk sac and larger ones in the connecting stalk; the latter are forming endothelium.