While upright serpents are typically lumped into the category of bass horns, there are dramatic differences among the instruments. Makers experimented extensively with materials, construction design, and fingering patterns. One important designation among the upright serpents is the configuration of finger holes for the lengthening of the air column. Using Mendelssohn's 1824 line drawing of the English bass horn (sent in a letter to his sister, Fanny), finger holes have been placed in order on the air column as a way to display their positioning.