"Cul-de-sac - a blind pouch or tubular cavity closed at one end"

Quite appropriate for describing a short dead-end street with houses along the length and around the circular end.

Anatomically, if a baby is born with an interrupting membrane in the colon a short distance above the anus ("cul"), as does occur once in a while, then there is a "blind pouch or tubular cavity closed at one end," and the poor little tyke has a "cul-de-sac."

Forty years ago this was presented as the origin of the term "cul-de-sac." Of course not everything we've been taught is necessarily true...but this one does make perfect sense.

Maybe this should have all been below the line, in "Words from Medicine"...