Oesophagus after barium swallow. Coloured X-ray of the upper body of a patient in side view, having swallowed barium meal into the oesophagus. The skull is at top; cervical vertebrae of the neck at upper left. The oesophagus is the tube (red) passing down from the throat into the stomach (not seen). In the neck the healthy oesophagus appears narrow as muscles contrict to swallow the barium meal. Barium salt is a substance opaque to X-rays and when swallowed highlights regions of the digestive tract. Here, the oesophagus is being examined to check for abnormalities such as reflux which occurs in hiatus hernia, ulcers, or tumours that may be cancerous.