CZECUINI, selthin ( Lat. meas. blind). A blind pouch in the human intestine into which the small intestine empties. It is also called the calm/ coii, or head of the colon. The colon, or large intestine, starts from it, in the hollow of the right iliac region, and runs upward. in its first part. The exeunt in man is too small to serve as an important part of the digestive tract, and is comparatively useless. From it springs the vermiform appendix (q.v.), generally posteriorly, the lumen of the appendix opening into the cavity of the exeunt. The microscopic structure of the walls of the exeunt does not differ in any essen tial from that of the rest of the large intestines. (See INTESTINES.) There are four coats, the mucous, the sub-mueous, the muscular, and the serous. The mucous coat consists of a lining of simple cylindrical epithelium, which is continu ous with the epithelium of simple tubular glands, which lie side by side, and are supported by a loose lymphoid connective-tissue stroma. Be
neath this is a single or double layer of nmsele, the museularis mucosa'. Beneath this is a vas cular connective-tissue layer, the sub-niucosa, which often contains lymph nodules. Passing outward from the sub-mucosa, the next coat is the muscular, divided into an inner layer; whose cells are disposed circularly to the lumen, and an outer layer, whose cells have their long axes directed longitudinally. In the ca.cum and large intestine the circular layer is usually thinner than in other parts of the gastrointestinal canal, and the outer layer is incomplete, being arranged in three longitudinal bands. which are shorter than the other coats of the intestines and give it a saeculated appearance. The serous coat is a thin connective-tissue layer covered over with a single layer of flat endothelial cells.