Verso of sheet 73: near-blank fragments
One fragment bears faint later charcoal marks; the other is entirely blank.
Both fragments mounted here were invisible before restoration. The verso of sheet 73a carries only a few charcoal lines not drawn by Leonardo—among them a crude, off-color figure sketch of the kind his pupils added to the backs of several military sheets—while the verso of 73b is entirely without writing or drawing. Faint show-through of the wheeled engine on the recto is also visible across the upper fragment.
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Later charcoal marks, not by Leonardo
According to the editorial note, the 73a verso bears only a few thick-charcoal lines that are not Leonardo's, including a crude and obscene figure sketch. It is compared to similar pupil-drawn sketches found on the versos of other military sheets in the codex.