Figure 1.

(a) Arrangement of the tibia–metatarsus joint for the adequate stimulation of the lyriform organ HS-8. (i) The metatarsus was kept at an angle of 50° to the fixed tibia. (ii) For stimulation under the white light interferometer, the metatarsus was deflected backwards (red arrow) and the forces resisting this deflection (blue arrow) measured at a distance of 22 mm from the pivot point. (b) Arrangement of the metatarsus–tarsus joint for adequate stimulation of the lyriform organ HS-10. The tarsus was deflected upwards (red arrow) and contacted the metatarsal pad at the mechanical threshold angle of 27°. At larger angles, the slits of organ HS-10 were compressed. The force resisting this deflection (blue arrow) was measured directly at the tarsus using the force transducer. (c) (i) Scanning electron micrograph (SEM) of the lyriform organ HS-8; (ii) SEM (courtesy of R. Müllan) of the metatarsal lyriform organ HS-10.