The distal quarter of the rectum is derived from the cloaca and can be viewed as a specialized "sensory organ". Only the proximal three quarters of the rectum stem phylogenetically from intestinal tissues. Therefore, only this upper portion has an associated mesorectum. A significant amount of data support the notion that profound differences exist between the enterogenic, upper segments and the cloacogenic, lower segment of the rectum: 1. differing supply with blood and lymph vessels, 2. embryologic and comparative anatomic findings, 3. the central support system provided by Denonvilliers' fascia, 4. specialized innervation, 5. malformations of the continence organ, 6. findings on magnetic resonance images and histologic macro sections, 7. findings on PET-CT images, 8. the muscular wall architecture of different portions of the rectum, 9. differences in basic function (storage vs continence), 10. location of most postoperative local recurrences of rectal carcinomas, even when complete mesorectal resection was performed, since hundred years.