Complex sentence: They take on the role of accenting the snare part (as the tenors usually share parts with the snare drum, playing exactly what the snares play rudimentally, but with movement); they also function as melodic percussion, as each drum has a different pitch.
Split into simpler sentences: They take on the role of accenting the snare part, and often times the tenor parts are rudimentally identical to the snare parts. Movement around the drums allows tenors to function as melodic percussion, as each drum has a different pitch.