a. Embryol. [SUB- 1 b.] Designating a layer of cells beneath the zona pellucida of an ovum, constituting the basis of the chorion.
1877. W. Turner, Hum. Anat., 864. The sub-zonal membrane consists essentially of a layer of cells, which was originally continuous with the cellular layer lining the inner surface of the proper amnion. Ibid. The formation of the amnion and sub-zonal outer layer of the persistent chorion.
