x1 is the duodenum (part of the small intestine) of x2.
Calque of Latin duodenum (digitorum) 'of twelve (fingers)': -gam- (< gai, twelve) + degji 'finger', removing the -j- to make it a freeword instead of a true compound. Compare Dutch twaalfvingerige darm, and its calque, Japanese 十二指腸 jūnishichō.