Fig. 3.
Conceptual hypothesis of the forces involved in lamellar closing. Blue arrows indicate the force exerted by surface tension (γ). Black arrows represent the Laplace pressure (p). (A) Dorsal view of a post mortem tongue (A. colubris) interacting with the air–nectar interface, showing the change in lamellar position with respect to the change in meniscal width (sagittally inclined yellow arrows). (B) Cross-section diagrams indicating the surface energy gradient on the internal menisci outside the nectar (Left) and at the beginning of the interface (Right). Yellow arrows depict meniscal width matching the points in the Upper panel. (C) Conceptual representation of the main forces acting on each lamella. Note that the minimum surface area state is achieved outside the nectar (Left) and the maximum surface area state is reached at the beginning of the interface (Right). When the tongue is leaving the nectar and the fluid no longer covers the outer wall of the lamella, the external component of the surface tension (γe) stops operating on the structure, Laplace pressure (p) begins to act and the surface area tends to be reduced by the internal component of surface tension (γi). The net result is the bending of the flexible lamella over the stiffer rod. Scale bar, 0.5 mm.