The portion of the small intestine that extends from the duodenum to the ileum.
Comment:
[taxon-note] "The jejunum is the middle section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms middle intestine or mid-gut may be used instead of jejunum.[Wikipedia:Jejunum]"