The word "prosoposternodymus" might seem like a daunting spelling challenge, but it can be broken down with the help of phonetic transcription. The first syllable, "proso," is pronounced with a short "o" sound, while "posterno" and "dymus" are straightforward phonetically. The trickiest part may be the middle syllable, "sternody," which is pronounced with a soft "e" sound rather than the expected "i." With a little practice, however, the spelling of this complex word can be mastered.
Prosopothoracopagus.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.