This is the ceiling of the temple, and its name is "zao3 jin3" (藻井). This "zao3 jin3" has some different form others. those "zao3 jin3" are circle usually, but this side is square.zao3 jin3 is used to show their craft. workmanlike carpenters do this to show their perfect craftsmanship.
The highest part is the narrowest part, and the lowest part is the widest part. Its shape like a triangle. If it's a cone, the carpenter usually use a centre decorate named "ming2 jing4" (明鏡). But on this picture, you can only see some elephant, right?
Because it's circle, it isn't corn. Did you got the right answer?










