The tube that connects the mouth and the stomach is the esophagus, according to Dictionary.com. The esophagus is a muscular passage found in vertebrate and invertebrate animals. It's sometimes referred to as the "gullet."
WebMD explains that the esophagus is about 8 inches long and is located behind the heart and trachea, or windpipe, and in front of the spine. WebMD notes that the esophagus passes through the diaphragm just prior to entering the stomach.
Muscles at the top of the esophagus are controlled consciously and are used during breathing, eating, vomiting, belching and in preventing food from entering the windpipe, according to WebMD. The muscles at the bottom of the esophagus are involuntary muscles, and they prevent acid and stomach contents from traveling back into the esophagus.