The chest and breasts belong to Cancer, but the more interesting fact about this part of the scheme is where a medieval person would have encountered it. The homo signorum was not confined to medical manuscripts. It appears in devotional books made for lay owners, most famously the Anatomical Man that opens the calendar of the Tres Riches Heures du Duc de Berry, illuminated for Jean de Berry in the first decades of the fifteenth century, where two figures stand back to back with the signs distributed over them.
That placement tells you what the doctrine was. It was not occult knowledge and it was not fringe. It sat in the calendar section of an expensive prayer book, next to the labours of the months, as part of the ordinary furniture of the year.
Cancer's assignment carries one of the scheme's standing disagreements. The sign takes the breasts and rib cage in every version, and the stomach in many, which puts it in competition with Virgo. Sources differ, and the atlas records both rather than choosing.
Printing did not kill the figure. It multiplied it, and the zodiac man stayed in popular almanacs into the nineteenth century and beyond, long after the medical theory supporting it had been abandoned by physicians. The atlas records all of this as history, not as anatomy.
Sources AstronomicaMarcus Manilius with The Zodiacal Miniature of the Tres Riches Heures of the Duke of Berry: Its Sources and MeaningHarry Bober