364
Z. RYCHTER
phase of development. In this phase the heart bulb becomes shorter but
wider and ceases to be an autonomous cavity of the heart (Rychter, 1959).
It is a suitable point here to draw attention to the fact that the heart
development of the chick embryos can be separated, from a functional
point of view, into three phases: (1) The initial phase in which peristaltic
contractions of the heart tube and heart loop occur (Patten et al., 1948).
(2) The second phase in which the developing bulbar cushions function
as valves separating the bulbar cavity from that of the ventricle on the
one hand and from that of the truncus on the other hand (first mentioned by Greil, 1903), continuing up to the time when the heart bulb
finishes its growth in length (i.e., till 4 days 16 hr of incubation—
Rychter, 1959). (3) The last phase, beginning with the incipient
ventricular septation, in which both the proximal and distal bulbar
cushions, functioning till now as valvular mechanisms, change into
ridge-like rudiments of the ventriculo-bulbar septum. The quasi-spiral
bulbar septum is not a result of a torsion, but of progressive asymmetrical concrescence of proximal and distal bulbar cushions (oriented
in two different planes) and by their modelling by the blood stream
(Rychter, 1959).
In some surviving human embryos (younger than 5 weeks), the same
final stages of bulbar septation, as seen in chick embryos, were observed
by microdissection (Rychter and Stafl, unpublished data).
IV. Simultaneous Experiments on the Heart Loop and Aortic Arches
A. Relation of the Incumbent and Transposed Aorta
Elimination of both the 6th aortic arches on the 4th day of incubation
caused not only the appearance of ventricular septal defects (of a
subaortic type) (Section III, A), but nearly always also an incumbent
aorta, in a haemodynamic way. On the other hand, because the transposition of the aorta into the right ventricle (Section III, D) from the
experimental standpoint, was produced by a primary disturbance of the
heart loop wall, it seemed necessary to regard the incumbent and
transposed aorta as being, in origin, two quite different congenital heart
malformations. But the same complete transposition of the aorta into
the right ventricle was brought about by simultaneous suppression of
the left developing atrium together with deformation of the bulboventricular groove on the 4th day of incubation (Rychter and Lemez,
1960b). Complete transposition of the aorta by a rhombic clip was
produced only up to the stage of 3 days 18 hr. The same intervention on
the 4th day led to partial transposition of the aorta characterized by
'Aortenventrikel' (Section III, D). The combined experiment sometimes decreased the left ventricular blood stream to such an extent, that
Z. RYCHTER
phase of development. In this phase the heart bulb becomes shorter but
wider and ceases to be an autonomous cavity of the heart (Rychter, 1959).
It is a suitable point here to draw attention to the fact that the heart
development of the chick embryos can be separated, from a functional
point of view, into three phases: (1) The initial phase in which peristaltic
contractions of the heart tube and heart loop occur (Patten et al., 1948).
(2) The second phase in which the developing bulbar cushions function
as valves separating the bulbar cavity from that of the ventricle on the
one hand and from that of the truncus on the other hand (first mentioned by Greil, 1903), continuing up to the time when the heart bulb
finishes its growth in length (i.e., till 4 days 16 hr of incubation—
Rychter, 1959). (3) The last phase, beginning with the incipient
ventricular septation, in which both the proximal and distal bulbar
cushions, functioning till now as valvular mechanisms, change into
ridge-like rudiments of the ventriculo-bulbar septum. The quasi-spiral
bulbar septum is not a result of a torsion, but of progressive asymmetrical concrescence of proximal and distal bulbar cushions (oriented
in two different planes) and by their modelling by the blood stream
(Rychter, 1959).
In some surviving human embryos (younger than 5 weeks), the same
final stages of bulbar septation, as seen in chick embryos, were observed
by microdissection (Rychter and Stafl, unpublished data).
IV. Simultaneous Experiments on the Heart Loop and Aortic Arches
A. Relation of the Incumbent and Transposed Aorta
Elimination of both the 6th aortic arches on the 4th day of incubation
caused not only the appearance of ventricular septal defects (of a
subaortic type) (Section III, A), but nearly always also an incumbent
aorta, in a haemodynamic way. On the other hand, because the transposition of the aorta into the right ventricle (Section III, D) from the
experimental standpoint, was produced by a primary disturbance of the
heart loop wall, it seemed necessary to regard the incumbent and
transposed aorta as being, in origin, two quite different congenital heart
malformations. But the same complete transposition of the aorta into
the right ventricle was brought about by simultaneous suppression of
the left developing atrium together with deformation of the bulboventricular groove on the 4th day of incubation (Rychter and Lemez,
1960b). Complete transposition of the aorta by a rhombic clip was
produced only up to the stage of 3 days 18 hr. The same intervention on
the 4th day led to partial transposition of the aorta characterized by
'Aortenventrikel' (Section III, D). The combined experiment sometimes decreased the left ventricular blood stream to such an extent, that