intestine joins the large intestine. Vertical lines The two vertical or mid-Poupart lines are drawn from the point midway between the anterior superior spine and the pubic symphysis on each side, vertically upward to the costal margin. The right one is the most valuable, as the ileo-caecal valve is situated where it cuts the intertubercular line. The orifice of the appendix lies an inch lower, at McBurney's point. In its upper part, the vertical line meets the transpyloric line at the lower margin of the ribs, usually the ninth, and here the gallbladder is situated. The left mid-Poupart line corresponds in its upper three-quarters to the inner edge of the descending colon. The right subcostal margin corresponds to the lower limit of the liver, while the right nipple is about half an inch above its upper limit. Quadrants and regions The abdomen can be divided into quadrants or regions to describe the location of an organ or structure. Classically, quadrants are described as the left upper, left lower, right upper, and right lower. Quadrants are also often used in describing the site of an abdominal pain. The abdomen can also be divided into nine regions. These terms stem from "hypo" meaning "below" and "epi" means "above", while "chondron" means "cartilage" (in this case, the cartilage of the rib) and "gaster" means stomach. The reversal of "left" and "right" is intentional, because the anatomical designations reflect the patient's own right and left.) The "right iliac fossa" (RIF) is a common site of pain and tenderness in patients who have appendicitis. The fossa is named for the underlying iliac fossa of the hip bone, and thus is somewhat imprecise. Most of the anatomical structures that will produce pain and tenderness in this region are not in fact in the concavity of the ileum. However, the term is in common usage. Other animals In arthropods the abdomen is built up of a series of upper plates known as tergites and lower plates known as sternites, the whole being held together by a tough yet stretchable membrane. The abdomen contains the insect's digestive tract and reproductive organs, it consists of eleven segments in most orders of insects though the eleventh segment is absent in the adult of most higher orders. The number of these segments does vary from species to species with the number of segments visible reduced to only seven in the common