Embryology of the Diaphragm and Congenital Diaphragmatic Hernia

A 22-week-old male fetus is evaluated by prenatal ultrasound and found to have a diaphragmatic defect on the left side. The defect allows herniation of abdominal contents into the thoracic cavity. Which of the following embryological structures failed to develop properly to result in this anomaly?

A 30-week-old female fetus undergoes prenatal imaging which reveals a defect in the formation of the diaphragm with herniation of abdominal contents into the thoracic cavity. The defect is located in the posterolateral aspect of the diaphragm. Embryologically, this region is derived from which of the following structures?