This is the third of the five terms, or bounds, into which the Egyptian table divides Scorpio. It runs from 11 degrees of the sign to 19, a stretch of 8 degrees held by Mercury. It opens where Venus's term closes at 11 degrees, and it gives way to Jupiter's term at 19 degrees, so a planet moving forward through Scorpio leaves Venus's bound and enters Mercury's at 11 degrees exactly.
Set out in degree order, the five terms of Scorpio run Mars (0-7), Venus (7-11), Mercury (11-19), Jupiter (19-24) and Saturn (24-30). At 8 degrees this is the widest of the five, against a narrowest of 4 held by Venus. The unevenness is not an accident of copying. No sign in the Egyptian table divides its five terms equally, and no two signs divide them the same way, which is why the table has to be consulted rather than derived.
The five rulers are the five planets visible to the naked eye. The sun and moon take no terms at all in this system, so each sign is shared out among Saturn, Jupiter, Mars, Venus and Mercury, every one of them holding exactly one stretch of it. A planet standing anywhere between 11 and 19 degrees of Scorpio is standing in Mercury's bound, and Hellenistic technique reads the lord of the bound from the degree occupied rather than from the sign as a whole. The table this atlas follows is the Egyptian one, transmitted by Vettius Valens in his Anthologies and recorded by Claudius Ptolemy in the Tetrabiblos, which stayed in ordinary use after Ptolemy set out his objections to it and offered boundaries of his own.