The duodenum extends from the pylorus at the bottom of the stomach to the jejunum, the second part of the small intestine. The duodenum is a common site for the formation of peptic ulcers.
The duodenum began as the Greek dodeka-daktulon, "twelve fingers", because they apparently observed that the duodenum is about twelve finger-breadths long. In German, the popular term for duodenum is Zwölffingerdarm, the "twelve-finger intestine".
The jejunum is a part of the small intestine which is half-way down the small intestine between its duodenum and ileum sections.
The term jejunum derives from the Latin jejunus, "empty of food, meager" or "hungry". The ancient Greeks noticed at death that this part of the intestine was always empty of food; so, from that came the jejunum.
The Latin jejunus also gave rise to jejune, "lacking in nutritive value and devoid of substance, significance, or interest" and "that which is dull".
A jejune argument is one that is empty (like the jejunum) and totally devoid of interest.