AbstractA descriptive study of a 5.5 mm, Horizon XIV human embryo with myeloschisis was made. It is the smallest specimen ever recorded with this anomaly which is considered the embryonic forerunner of the common lumbo‐sacral meningomyelocele. The lesion extended from the twenty‐fifth existing somite caudally for 1 mm and was characterized by an everted neural plate, a loss of cellular polarity, asymmetry with a spread of neural tissue to the left and possibly a defective external limiting membrane of the neural tube. These findings indicate the lesion occurred before closure of the neural tube and are consistent with the observations of Patten ('53). They definitely do not support Gardner's ('60) hypothesis that rupture of a closed neural tube causes these lesi
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