After the descending chromatic line from F4, the melody eventually leads us back to the starting position. We keep running in sixteenth tuplets and the alternating pattern from the previous line continues: uneven-numbered notes dominate the melody, whereas even-numbered notes give the harmonic context. At least this is what it feels like to me. If I hum the melody, I instinctively simplify the opening descending line to a chromatic scale and the following part to second intervals repeated in three octaves.
First we have the intervals e-d and d-c. Note the slight deviations in the second measure (f becomes e, b leads up to the next line).
Then the intervals a-g♯ and g♯-f♯, ending in e, which leads back to the initial f of the chromatic line.
As in the first part, a bit of wrist rotation helps maintaining the rhythm while keeping the hand relaxed.