Comparison of two sets of twins. A normal set of twin lambs is shown at the right. A set of postmature lambs with deformed skulls and brains is shown at the left. The affected fetuses continued to grow in utero but failed to initiate parturition due to a nonfunctional hypophysis, hence a failure to release ACTH. Consequently the adrenal glands did not produce cortisol to initiate parturition.
Drost M (1967)