Legends to Figures
Figure 1. The images are made by reconstructing the developing
systemic venous tributaries in developing human embryos, using the
interactive pdf files available from Reference #2. The developing heart
is shown as viewed from behind. At Carnegie stage 12 (panel A), both
sinus horns are in direct continuity with the atrial component of the
developing heart tube (white arrows with red borders). One stage later,
as shown in panel B. the left sinus horn has become incorporated into
the developing left atrioventricular junction, losing its connection
with the left side of the developing atrial component (white star with
red borders). The systemic venous sinus then connects only with the
cavity of the developing right atrium. Note the location of the dorsal
mesocardium, which has served as the fulcrum for the remodelling.
Figure 2. The images are from a three-dimensional episcopic
dataset prepared from a human embryo at Carnegie stage 14. The venous
valves now mark the boundary between the systemic venous sinus and the
developing right atrium, as seen in the four chamber section shown in
Panel A. Panel B is a section showing how the systemic venous
tributaries now open within the confines of the venous valves. With
further development, the left sinus horn will become the coronary sinus.
Figure 3. The images are four-chamber sections through
three-dimensional episcopic datasets prepared from developing mouse
embryos. Panel A shows the arrangement at embryonic day 14, when
septation is complete, while panel B shows the situation at term. Both
venous valves persist.
Figure 4. The images show persistence of the right venous valve
in two human hearts. Panel A shows an example where the valve has
persisted as the Eustachian valve, guarding the mouth of the inferior
caval vein, as a prominent Thebesian valve guarding the mouth of the
coronary sinus, but also as a valve guarding the mouth of the superior
caval vein. The valve at the orifice of the superior caval vein is
reinforced by a muscular strap, which is the spurious septum. The arrow
shows how the strap passes in front of the entrance of the superior
caval vein to the right atrium. Panel B shows an example where the valve
has become aneurysmal, producing a windsock that has prolapsed through
the tricuspid valve.
Figure 5. The images show various human hearts with persistence
of the left venous valve (white arrow with red borders). Panel A shows a
four chamber cut across the oval fossa. In panel C, there is also
persistence of the venous valve guarding the mouth of the superior caval
vein (red arrow with white borders).