Caption: "Drawing by Theodoros Pelecanos of Corfu (fl. later 15th century), in an alchemical tract titled Synosius (1478)." (Slightly edited.)
Not a viscious circle---maybe.
The snake or dragon eating its own tail is the Ouroboros (tail-devourer) which is an ancient symbol invented in ancient Egypt.
Credit/Permission:
Theodoros Pelecanos of Corfu
(fl. later 15th century),
1478
(uploaded to Wikipedia
by User:Carlos adnero,
2007) /
Public domain.
Image link: Wikipedia:
File:Serpiente alquimica.jpg.
Local file: local link: ouroboros.html.
File: Art_o file:
ouroboros.html.