A schematic of the axoneme cross-section (viewed from the base) with DMTs numbered 1–9 (ref. 14 ). The bridge (dark red) that connects DMT1 and DMT2 may set the bending plane (the rigid-bridge hypothesis). The green and red arrows indicate the material frame of the axoneme (vectors {e}_{1} and {e}_{2} span the cross-sectional plane, with {e}_{1} pointing towards the bridge and {e}_{2} being orthogonal to {e}_{1} , while {e}_{3} is normal to the cross-section, pointing along the centre line). Dynein motors (green) are permanently attached to one DMT and transiently interact with their clockwise neighbour DMT.
