Sentence:  Coincident with the dropping out of the fifth or sixth primary is the molt of the outermost <WSD>tertiary</WSD>, followed by the adjoining <WSD>tertiary</WSD>, and then the third <WSD>tertiary</WSD>, which in most passerine birds is the last or innermost. 
Meaning of the word marked with <WSD> tags:  A tertiary feather; a tertial.