Fol. 13v

This page contains more anatomical observations about the alula, which Leonardo compares to ‘a thumb … at the service of the wings in the same way that the nails serve the cat when he climbs a tree’. He then adds other considerations on the tail, which helps the bird to remain in equilibrium.

«Il dito grosso "n" della mano "m" "n" è quello che quando la mano si abbassa si trova ad abbassarsi più che la mano stessa in modo che chiude e impedisce la fuga dell'aria in modo che lì l'aria si condensa e resiste al remare dell'ala, e per questo la natura ha dotato il dito grosso di un osso di tanta forza, al quale si congiungono nervi fortissimi e penne corte e di maggior resistenza di quelle delle ali»
(The thumb n of hand m, n is that which, when the hand goes down, is found to lower more than the hand itself so that it closes and prevents the air from escaping so that the air condenses and resists the rowing of the wing, and for this reason nature had equipped the thumb with a very strong bone, to which are added extremely strong ligaments and short feathers and a greater resistance than those of the wings.)

NOTE. For each page of Leonardo’s Codex we provide a brief summary, with the quotation of one that page’s most significant passages edited in modern Italian, with an English translation.

translation by Kim Williams