Light micrograph of a sessile serrated lesion, which is a type of polyp that can occur in the human colon. These polyps are often removed during colonoscopy procedures and then diagnosed by pathologists who examine the polyp tissue microscopically. The characteristic feature of a sessile serrated lesion is serration, or the jagged inner contour, of the colon crypts (roughly round and elongated structures throughout image that contain irregular white spaces). By definition, the serration extends to the bottom of the epithelium (surface lining) which rests on a layer of smooth muscle (pink line at the bottom of the image) called the muscularis mucosa. Haematoxylin and eosin stained tissue section. Magnification: x100 when printed at 10cm wide.