Sentence:  This means that in the metrical sequence... recited in ordinary speech rhythm, the princeps occupied a slightly shorter time than the <WSD>biceps</WSD> (5:6), and if a long syllable was used to fill the <WSD>biceps</WSD> it had to be dragged a little... 
Meaning of the word marked with <WSD> tags:  A point in a metrical pattern that can be filled either with one long syllable (a longum) or two short syllables (two brevia)