This is the fifth of the five terms, or bounds, into which the Egyptian table divides Cancer. It runs from 26 degrees of the sign to 30, a stretch of 4 degrees held by Saturn. It opens where Jupiter's term closes at 26 degrees, and it closes the sign at 30 degrees, so Saturn holds the last 4 degrees of Cancer before the boundary into the next sign.
Set out in degree order, the five terms of Cancer run Mars (0-7), Venus (7-13), Mercury (13-19), Jupiter (19-26) and Saturn (26-30). At 4 degrees this is the narrowest of the five, against a widest of 7 held by Mars and Jupiter. 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 26 and 30 degrees of Cancer is standing in Saturn'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.