The stomach is a muscular and membranous bag situated one-fourth in the epigastric region, and three-fourths in the left hypochondriac region. It is about 10 inches long from right to left, and is curved on itself, so that the lower surface is long and convex and the upper surface short and concave ; these curves are called the greater and lesser curvatures. There are two openings, one from the oesophagus, called the cardiac orifice, which lies behind the seventh costal cartilage, about an inch to the left of the sternum, and opposite to the tenth dorsal vertebra ; it is the most fixed portion of the stomach. The lower opening into the first part of the small intestine is called the pyloric orifice ; when the stomach is empty it is about in the middle line, but as the stomach gets distended, it moves to the right towards the gall-bladder. The fundus is the highest part ; it reaches to the sixth costal cartilage or higher, behind the apex of the heart.

Relations.—Above, apex of heart, base of left lung, diaphragm between ; to the left (and behind), the spleen ; to the right, right lobe of liver and gall-bladder ; in front, left lobe of liver ; behind, pancreas, thoracic duct, spleen, aorta, inferior vena cava, solar plexus ; below, transverse colon.

The stomach has five coats ; the inner three are continuations of the coats of the oesophagus. The mucous membrane is drawn up into folds when the stomach is empty ; it contains numberless small glands which secrete mucus, which keeps the surface moist.

The small intestine is divided into three parts :

1.  Duodenum.

2.   Jejunum.

3.   Ilium.

There is no real division between these ; altogether they are about 20 feet in length, and are coiled in the middle of the abdomen. The ilium opens into the larger intestine. This opening is guarded by a fold of mucous membrane called the ilio-caecal valve. The large intestine is about 6 feet long ; it lies on outer sides, and in front of the small intestine ; it is also divided into three parts. The divisions are as follows :

Caecum.

1.  Ascending colon. Hepatic flexure.

2.   Transverse colon. Splenic flexure.

3.   Descending colon. Sigmoid flexure. Rectum.

The caecum, a short, blind pouch, lies in the right iliac fossa. At the back and inner part of the caecum is a narrow tube from 3 to 6 inches long, called the vermiform appendix.