The inside of the pouch is an open reservoir. Like a balloon. The seam, or stitching, seen in your posted diagram is only to show where the two limbs were stapled together. If the pouch was two separate limbs stapled together the stool would fill up only in one limb before you feel pressure to go to the toilet. What would be the use of the other limb? Ask your surgeon at your next appointment if the pouch is hollow, or stapled into two separate limbs. Or, Google for real images of the inside of a j pouch. You will see "owl's eyes" at the top (the view of the camera looking into the pouch via the anus) and an empty, hollow chamber that is the pouch. No stitching or stapled tissue. Not separate limbs. It took me a while to understand this concept, but it makes perfect sense, and my surgeon confirmed this. He has created hundreds of pouches in his long career.