| aperture lies obliquely, and is guarded by two halves, the right and left venous valves; above the opening these unite with each other and are continuous |
 |
FIG. 464– Dorsal surface of heart of human embryo of thirty-five days. (From model by His.) (See enlarged image)
|
 |
FIG. 465– Interior of dorsal half of heart from a human embryo of about thirty days. (From model by His.) (See enlarged image)
|
with a fold named the septum spurium; below the opening they fuse to form a triangular thickening—the spina vestibuli. The right venous valve is retained; a small