(f) Small intestine(1) Structure : Endodermal, longest part of alimentary present in the abdominal cavity, supported by a peritoneal membrane called mesentery. Wall of jejunum and ileum has circular or spiral internal fold called fold of kerckring or valvulae conniventes. Also numerous finger like projection called villi project from the wall of lumen, increasing internal surface are about eight time. The distal end of ileum is leads into the large intestine by ileo-caecal valve in man but in rabbit sacculus rotundus and ileo-coecal valve both are present.