The congenital abnormality of the ileum illustrated below

Meckel's diveiculum occurs in the ileum, usually within 30 cm of the ileocecal valve, and is present in approximately 2% of normal persons. It represents incomplete involution of the vitellointestinal duct and always arises from the antimesenteric border of the intestine. Heterotopic gastric or pancreatic tissue may be present in about one-half of cases. Peptic ulceration, which occurs as a result of acid secretion by heterotopic gastric mucosa, is usually located in the adjacent ileum. Complications include perforation, ulceration, intestinal obstruction, intussusception, and neoplasms, including carcinoid tumors. Reference: Robbins & Cotran Pathologic Basis of Disease, 9edition