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Identify the loops of jejunum and ileum, which are the second and third parts of the small intestine, respectively. The division of the small intestine into the jejunum and ileum is arbitrary. The proximal two-fifths of the small intestines is the jejunum, and the distal three-fifths is the ileum. The coils of the small intestine lie obliquely across the abdomen from the left upper quadrant to the right lower quadrant. Coils of the ileum usually descend into the pelvic cavity.
Note that the external surface of the jejunum and ileum is relatively smooth.Links and References:
Grant's: 2.71, 2.76
Netter: 253, 254
Rohen/Yokochi: 287, 288, 290