Four half-men awkwardly holding hands inside four concentric bands.

[MarcoP]

In the Cava de’Tirreni ms, the text explains the peculiar arrangement. For instance, the top-left quadrant: "Aer calidus et humidus sociatur igni / per calorem, aque per humorem" Air is hot and wet. It is related with fire by heat, and with water by humidity. 
Below, in red: "Aer iungitur aqua" Air is conjunct with water (but You are not allowed to view links. Register or Login to view. also means "to clasp hands"). The rationale is that each of the four elements is made of different combinations of two of the four Galenic qualities (hot/cold, wet/dry): couples of elements share a single quality (and opposite elements share none). This is cleverly illustrated by each element holding hands with the two contiguous elements with which it shares a quality.