The digestive system includes the alimentary canal and various organs connected with it. The greater part of the digestive system lies within the abdomen. The alimentary canal consists of the following parts : Mouth, pharynx, oesophagus, stomach, duodenum, small intestine (jejunum, ileum), large intestine, rectum; and the organs connected with it are- salivary glands, liver, pancreas. The whole of the alimentary canal consists of structures formed of one or more muscular coats lined with mucous membrane.

Mouth

The Mouth is the first division of the alimentary canal, and contains the parts necessary for mastication and the openings of the ducts of the salivary glands. The food passes from the mouth into the pharynx, a large space at the back of the nose and mouth, containing in its lower half the greater part of the tongue and the larynx. The pharynx ends at the level of the sixth cervical vertebra, and from it pass the larynx and trachea in front and the oesophagus behind.

Esophagus

The Esophagus is the part of the digestive canal which leads from the pharynx to the stomach. It is a muscular tube, flattened by the trachea and the other structures lying on it. It lies in the thorax and extends from the sixth cervical vertebra to the eleventh dorsal vertebra, where it passes through the diaphragm and enters the stomach. It is closely applied to the vertebral column, lying behind the other structures in the thorax.

Abdominal Cavity

The Abdominal Cavity, which contains the rest of the alimentary canal, is bounded above by the diaphragm, below by the pelvic floor, posteriorly by the lumbar vertebrae, and anteriorly and laterally by the abdominal muscles and iliac bones. The false pelvis is included in the abdominal cavity. The abdomen is divided up into nine regions by two horizontal lines and two vertical lines.

The subcostal line, the upper of the two horizontal ones, is drawn round the trunk at the level of the lower border of the -tenth costal cartilage. The intertubercular line-the lower horizontal one- is drawn at the level of the tubercles on the crests of the iliac bones, about two inches behind the anterior superior spine. This is the highest point of the iliac crests. The vertical or Poupart's lines are drawn from a point midway between the anterior superior spine of the ilium and the symphysis of the pubis.

By this means we have three regions in the middle line-the epigastric, umbilical, and hypogastric, and laterally the hypo-chondrium, lumbar, and iliac regions.