It's always exciting whenever identifying an esoteric book hitherto undetected in Sir Thomas Browne's library, especially when the opportunity arises to share an image which the physician-philosopher once cast his eye upon. This fantastic medieval illustration of Mercurius with his caduceus and chariot wheels depicting the zodiac signs of Virgo and Gemini is from the astrologer/astronomer Guido Bonati's De Astronomia..
According to the Wikipedia entry Guido Bonati of Forli, Italy (d. circa 1300) was the most celebrated astrologer in Europe in his century. His book De Astronomia, written around 1277 was reputedly the most important astrological work produced in Latin in the 13th century. Bonati's mentioned in Dante's Inferno Canto 20 line 118.
There seems to be some ambiguity over how his name is spelled, both Bonati and Bonatti occurring in sources. The entry in the 1711 Sales Catalogue of Browne's library states Bonati, however Dante writes of him as Bonatti. Either way, it's yet more evidence of Browne's predilection towards the reading and study of esoterica as the Wikipedia list of esoteric books in Browne's library highlights.
Another illustration from the 1550 Bonati edition owned by Browne. The counterpart of Mercurius in alchemy is Saturnus ruler of Capricorn and Aquarius depicted here upon his chariot wheels. Note how each planetary chariot is towed by quite different creatures. Saturnus holds a scythe symbolic of his links to agriculture and a remnant of his association to Father Time who appears on New Year's Eve.
 1711 Sales Catalogue page 28 no.10
Full entry - Guido Bonati de Astronomia Tract x. universum quod ad Indiciariam rationem Nativatum, &c attinet comprehend. 1550
Wiki-link - Guido Bonati