The entire small intestine has<unk>  of mucous membrane. The majority extend transversely around the cylinder of the small intestine, for about one-half or two-thirds of its circumference. Some form complete circles. Others have a spiral direction. The latter usually extend a little more than once around the bowel, but occasionally two or three times. The larger<unk>  are about 1 cm. in depth at their broadest part; but the greater number are smaller. The larger and smaller<unk>  alternate with each other. These can increase the surface area of the small intestine threefold. Distribution They are not found at the commencement of the duodenum, but begin to appear about 2.5 or 5 cm beyond the pylorus. In the lower part of the descending portion, below the point where the bile and pancreatic ducts enter the small intestine, they are very large and closely approximated. In the horizontal and ascending portions of the duodenum and upper half of the jejunum they are large and numerous. From this point, down to the middle of the ileum, they diminish considerably in size. In the lower part of the ileum they almost entirely disappear; hence the comparative thinness of this portion of the intestine, as compared with the duodenum and jejunum. Difference from other gastrointestinal<unk>  Unlike the gastric<unk>  in the stomach, they are permanent, and are not obliterated when the intestine is distended. The spaces between<unk>  are smaller than the haustra of the colon, and, in contrast to haustra,<unk>  reach around the whole circumference of the intestine. These differences can assist in distinguishing the small intestine from the colon on an abdominal x-ray.
Circular folds
Synechia 
Venous translucence
Siegrist streaks
Owl's eye appearance
Mayer waves
Stretch marks
Knuckle pads