Does the Stage 16 Embryo in Hamburger–Hamilton’s “Series of Normal Stages in the Development of the Chick Embryo” Have a Potential “Conotruncal” Heart Defect?

Abstract

The classical Hamburger and Hamilton (HH) paper demonstrates the normal stages of development of the chick embryo that have been extensively used as the basis of understanding normal and abnormal development of the chick embryo heart. Careful examination of the series of images published in this seminal paper indicates that the cardiac images of stage 16 embryo shown in this article may reflect an abnormally developed heart. In this article, the argument is presented that the embryo depicted in the HH paper is not normal, but instead inflicted with a conotruncal heart defect.