EXPERIMENTAL-STUDY OF THE DEVELOPMENT OF THE TRUNCUS ARTERIOSUS OF THE CHICK-EMBRYO HEART .1. TIME OF APPEARANCE

The time of appearance of the truncus arteriosus was studied in the ch ick embryo using an in ovo labeling technique. Three hundred embryos a t stages 13-18 of Hamburger and Hamilton were selectively labeled at t he distal end of the heart tube, using gelatine-india ink label; 122 o f these embryos were reincubated and 111 of them reached stages 25-28. In these stages the final location of the label was determined. Only 95 of these embryos showed both a normal heart and a label located in it. The remaining embryos were discarded due to abnormal cardiac morph ology or because the label was not found. Embryos labeled at stages 13 -14 had label in the conus in 42.8% of the cases and in the boundary b etween the conus and the truncus arteriosus in 57.1% of the cases. Lab el placed at stages 15-16 was located in the conus in 6.1% of the case s, in the boundary between the conus and the truncus arteriosus in 44. 8% of the cases, and in the truncus arteriosus in 48.9% of the cases. Finally, label placed at stages 17-18 was located in the boundary betw een the conus and the truncus arteriosus in 18.7% of the cases and in the truncus arteriosus in 81.2% of the cases. Our results permit us to conclude that the truncus arteriosus appears in the chick embryo as e arly as stages 15-16 of Hamburger and Hamilton (50-56 hours of incubat ion). (C) 1993 Wiley-Liss, Inc.