Step 1

Embryology 3

A 4-hour-old term male infant is being examined by a neonatologist. The mother is 26 years old gravida 1, para 1 and has no history of vaccination. She reports a few episodes of fever during the first and second trimester. Delivery was uneventful, and the infant was noted to have low birth weight. On physical examination, he is found to have absent red reflex in both eyes, a small head, and a continuous murmur over the left sternal border.

Which of the following is the embryological origin of the structure causing the murmur?

  • A) Allantoic duct
  • B) Bulbus cordis
  • C) The 5th branchial arch
  • D) The 6th branchial arch
  • E) Truncus arteriosus


Husban Hamil


Dr. Ted O'Connell

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