SMALL INTESTINE, DRAWING. SMALL INTESTINE, DRAWING In man, the small bowel, which begins with the duodenum at the pyloric opening of the stomach and terminates into the large bowel, is approxima-tely 7 meters long. The longest part of the small intestine is freely folded within the abdominal cavity and only attached to the posterior abdominal wall by a membranous extension of the peritoneum called the mesentery.