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Now study the anatomical features of the other two portions of the small intestine, the jejunum and ileum. The upper two-fifths of the small intestine is the jejunum; the lower three-fifths is the ileum. There is no distinct gross anatomical site to mark the transition from jejunum to ileum.
Note: The small intestine can be studied in situ or it may be removed for study outside the abdominal cavity. Ask your instructor which procedure is preferred.Links and References:
Grant's: 2.69
Netter: 280
Rohen/Yokochi: 279, 278