How the wing-tip pinions catch a following wind to lift the bird
Struck from behind while flying aslant, the bird takes the wind on its outspread wing-tips and is driven upward
Leonardo explains the use of the thick pinions at the wing-tips when a bird is struck from behind by the wind while lying aslant on the air that sustains it. The wind then strikes full on those outspread tip feathers, driving the bird upward and increasing its motion, refreshed by the wind's own motion. Small marginal sketches show a bird in flight and a wings-spread bird seen head-on. The sheet carries a further block of mirror-script text not included in the transcription.
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The thick wing-tip pinions catch a following wind
The thick pinions at the wing-tips come into play when the bird is struck from behind by the wind and stands aslant upon the air that holds it up. The wind strikes full on those tip feathers turned toward it. So the bird is thrust upward, its motion increased and refreshed by the motion of the wind.
Marginal sketches of a bird and outspread wings
A small bird in flight is drawn at upper right, and beside the lower text a wings-spread bird is sketched head-on with its long primary feathers splayed. The head-on view illustrates the outspread wing-tips discussed in the note.