If you perceive of the body as a microcosm of all of creation, you had better pay attention to the universe when you are treating a patient. The medieval sensibility closely linked the stars and the humors of the body. This famous, hand-colored illustration of "zodiac man" comes from a 1500 printing of Joannes de Ketham's Fasciculus Medicinae. Originally printed nine years earlier, it is thought to be the first medical textbook in the era of print.
The text surrounding zodiac man gives practical, and crucial, advice to physicians about the proper timing for medical procedures. Treating maladies of the head would be very dangerous when the sun is in Aries because of the sign's anatomical association.
The concepts linking the zodiac with health persisted long after more modern medical practices came into fashion. In his 1740 Poor Richard's Alamanck, Benjamin Franklin repeats the iconic medical chart as a handy guide for medical diagnosis and treatment.
To see Ketham, ask for Incunabula 74, and for the 18th-century survival of medieval medicine, ask for Rare PS749.A2 1740. You can also see the National Library of Medicine copy of Ketham online.