The quart guitar
The Quart Guitar is tuned four notes up - that makes it the same pitch as the requinto.
The tuning is A D G C E A
Like the requinto, the quart is short-scale, but usually with a different scale length to the requinto - a figure of 480mm is often quoted. The shorter scale length requires thicker strings, leading to a mellow sound.
The quart bass guitar
And underneath, there's the Quart Bass - four notes down (like hago's bass), but often on a standard scale neck.
The tuning is B E A D F# B
The lack of neck length means that heavier strings are needed and these lack the brilliance and sustain of a long-scale instrument.
Curiously, the tuning is not an octave under the Quart... see why here