Plate 19
|
PLATE NUMBER |
STAGE |
TIME |
ORIENTATION |
IMAGE |
|
19 |
Small yolk plug stage Embryo stage 12 1/2 |
14 h 30 min p.f. |
Dorsal
Ventral |
Posterior transversal sections |
Small yolk plug stage (Embryo stage 12 1/2)
A: Zone of Involation
The lining of the central yolk plug is made of prospective endodermal epithelium prior and the outer layer of the blastocyst is made of endodermal epithelium prior to their involution. The preinvolution prospective mesoderm in the subepithelial region has a disordered cell arrangement.
B: Postinvolution Mesoderm
The notochord is clearly visible in the dorsal mesoderm and is surrounded on each side by converging paraxial mesoderm. In the ventral region, the mesoderm is extended and flatens laterally. Thre is no clear border between the lateral and ventral mesoderm and endodermal yolk mass.