E X P E R I M E N T S ON EMBRYONIC AORTIC ARCHES 365
the concrescence of the ventricular septal components, undisturbed by
the blood stream, was so abundant that the extremely hypoplastic
rudimentary left ventricle was separated from its outlet (aortic portion
of the bulb). Because no atrial septum was present as well, the cases
represented actually a cor biloculare with the heart apex formed by the
right ventricle. The embryos, nevertheless, were in good condition.
The conclusion may be drawn that the morphogenetic movement of
the heart bulb is also governed by the blood stream reaching it from the
left ventricle.
Because the aorta was held in the incumbent position by the right
ventricular blood stream passing through the unclosed ventricular
septum, it was supposed that the effect would be strengthened by
diminishing the left ventricular blood stream. The following experiment was conducted: on the 4th day of incubation suppression of the
developing left atrium was performed together with suppression of both
6th aortic arches (Rychter and Lemez, 1960b). To our surprise, the
heart bulb persisted in its original relation to the ascending part of the
heart loop, so that a transposition of the aorta into the right ventricle
developed. Here, too, the left ventricle was separated from its outlet as
mentioned above. The experiment produced transposition of the aorta
solely in a haemodynamic way by a combination of two experimental
interventions, neither of which alone could ever cause it.
The incumbent aorta and the aorta transposed into the right ventricle, judged from the point of view of the ratio of the right and left
ventricular blood streams, appear as two stages of the same heart
malformation (i.e., the morphogenetic movement of the heart bulb
changed in a haemodynamic way).
From the viewpoint of the location of damage to the heart loop and
aortic arches, two different heart malformations are concerned: the
incumbent aorta is solely accessory to having both 6th aortic arches
undeveloped (pulmonary stenosis), while aortic transposition into the
right ventricle is, according to the present conception, a direct result of
the early stopping of bulbar movement.
It is evident that both statements are in a sense true, depending on
the point of view leading to the arrangement of experimental conditions.
All the experiments, in spite of the knowledge gained being relative
only, contribute nevertheless to a deeper understanding of the origin
and development of the transposition of the aorta into the right
ventricle and of the mutual interactions in the cardiovascular system.
B. Dependence of the Critical Period on Experimental Procedure
Goerttler (1957) estimated that the critical period for the origin of
transpositions of the great vessels in chick embryos lasted from the
the concrescence of the ventricular septal components, undisturbed by
the blood stream, was so abundant that the extremely hypoplastic
rudimentary left ventricle was separated from its outlet (aortic portion
of the bulb). Because no atrial septum was present as well, the cases
represented actually a cor biloculare with the heart apex formed by the
right ventricle. The embryos, nevertheless, were in good condition.
The conclusion may be drawn that the morphogenetic movement of
the heart bulb is also governed by the blood stream reaching it from the
left ventricle.
Because the aorta was held in the incumbent position by the right
ventricular blood stream passing through the unclosed ventricular
septum, it was supposed that the effect would be strengthened by
diminishing the left ventricular blood stream. The following experiment was conducted: on the 4th day of incubation suppression of the
developing left atrium was performed together with suppression of both
6th aortic arches (Rychter and Lemez, 1960b). To our surprise, the
heart bulb persisted in its original relation to the ascending part of the
heart loop, so that a transposition of the aorta into the right ventricle
developed. Here, too, the left ventricle was separated from its outlet as
mentioned above. The experiment produced transposition of the aorta
solely in a haemodynamic way by a combination of two experimental
interventions, neither of which alone could ever cause it.
The incumbent aorta and the aorta transposed into the right ventricle, judged from the point of view of the ratio of the right and left
ventricular blood streams, appear as two stages of the same heart
malformation (i.e., the morphogenetic movement of the heart bulb
changed in a haemodynamic way).
From the viewpoint of the location of damage to the heart loop and
aortic arches, two different heart malformations are concerned: the
incumbent aorta is solely accessory to having both 6th aortic arches
undeveloped (pulmonary stenosis), while aortic transposition into the
right ventricle is, according to the present conception, a direct result of
the early stopping of bulbar movement.
It is evident that both statements are in a sense true, depending on
the point of view leading to the arrangement of experimental conditions.
All the experiments, in spite of the knowledge gained being relative
only, contribute nevertheless to a deeper understanding of the origin
and development of the transposition of the aorta into the right
ventricle and of the mutual interactions in the cardiovascular system.
B. Dependence of the Critical Period on Experimental Procedure
Goerttler (1957) estimated that the critical period for the origin of
transpositions of the great vessels in chick embryos lasted from the