302 
THE DEVELOPMENT OF THE HEART IN MAN. 
Fig. 12. The same model from the right side after removal of the lateral wall of the right atrium and 
ventricle, and of the right venous valve. 
Fig. 13. Caudal portion of model of heart of 20-mm. embryo, divided horizontally. 
Fig. 14. Ventral aspect of model of 30-mm. embryo. 
Fig. 15. Same model viewed from the right after removal of the lateral wall of the atrium and of the 
right venous valve. 
Fig. 16. Interior of the left atrium of heart of a fully developed child, with foramen ovale I persisting 
in addition to foramen ovale II. 
The lettering in the figures is as follows : — 
A. = Bulbar cushion A. 
Ao. = Aorta. 
A.S. = Aortic sinus. 
Atr. = Atrium. 
A.-V.V. = Atrio-ventricular valve. 
A.-V.B. = Atrio-ventricular bundle. 
A. F. = Annulus fibrosus. 
B.Cu. = Bulbar cushion. 
B. = Bulbar cushion B. 
B. C. =Bulbus cordis. 
B. V. = Bulbo-ventricular. 
C. S. = Coronary sinus. 
E.T. = Endothelial tube. 
End. Cu. = Endocardial cushions of the atrial 
canal. 
F.O. i and I Foramen ovale primuni and secun- 
F.O. ii .1 ~ dum. 
Inf. = Infundibulum of right ventricle. 
I.V.C. = Inferior vena cava. 
I.-V.S. = Intersepto-valvuIar space. 
I.V.F. = Interventricular foramen. 
L.A. = Left atrium. 
R.A. = Right atrium. 
L.C. = Lateral cusp of atrio-ventricular 
valve. 
M.C. = Medial cusp of atriowentricular valye. 
L.V. = Left ventricle. 
L. A.-V.O.'I _ Left and right atrio-ventricular 
R. A.-V.O. J openings. 
L.V.O. = Left venous ostium. 
R.V.O. = Right venous ostium. 
L.V.V. and! T n ■ j ■ . . , 
- =Lett and right venous, valves. 
R.V.V. J 
0. = Opening of sinu-atrial chamber into 
the right atrium. 
P.A. = Pulmonary artery. 
P.V. = Pulmonary vein. 
R. Y. = Right ventricle. 
R. P.V. = Right pulmonary vein. 
S. i = Septum primum atriorum. 
S. -A.O. ■ Sinu-atrial orifice. 
S. B. = Septum of the bulbus cordis. 
S. Y. = Sinus venosus. 
'S.V.C. = Superior vena cava. 
Sin. At. = Sinu-atrial chamber. 
T. A. =Truncus arteriosus. 
T.V. = Tensor valvulae. 
V.Ao. = Ventral aorta. 
V.C.S. = Vena cava superior. 
