Outside the amniotic ectoderm is a thin layer of mesoderm, which is continuous with that of the somatopleure and is connected by the body-stalk with the mesodermal lining of the chorion.    From Wordnik.com.  [I. Embryology. 11. Development of the Fetal Membranes and Placenta] Reference

In reptiles, birds, and many mammals the amnion is developed in the following manner: At the point of constriction where the primitive digestive tube of the embryo joins the yolk-sac a reflection or folding upward of the somatopleure takes place.    From Wordnik.com.  [I. Embryology. 11. Development of the Fetal Membranes and Placenta] Reference

The lateral mesoderm splits into two layers, an outer or somatic, which becomes applied to the inner surface of the ectoderm, and with it forms the somatopleure; and an inner or splanchnic, which adheres to the entoderm, and with it forms the splanchnopleure (Fig. 16).    From Wordnik.com.  [I. Embryology. 5. Segmentation of the Fertilized Ovum] Reference

By the forward growth and flexure of the head the pericardial area and the anterior portions of the primitive aortæ are folded backward on the ventral aspect of the fore-gut, and the original relation of the somatopleure and splanchnopleure layers of the pericardial area is reversed.    From Wordnik.com.  [V. Angiology. 3. Development of the Vascular System] Reference