Rib

The white outlines are ribs.

Vaulted ceiling and ribs

Vaulted ceiling with ribs. The yellow parts that outline the blue surfaces are the ribs.

Guttae

The guttae are the little "drops" below a triglyph.

More on Architecture

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Quoining

Triglyph

The trighlyph is to the left of the B. The column below it is Doric. The little cork-like things are called guttae.