a) The food passes down from the mouth to the stomach via oesophagus. The food is in the form of slippery mass combined with saliva, called bolus.
b) The food pipe walls are made up of two different types of muscles- inner layer consists of circular muscles, while the outer layer consists of longitudinal muscles.
c) Contraction of the inner circular muscles results in narrowing of the oesophagus just behind the bolus, so it is squeezed forward in the food pipe.
d) While, the contraction of longitudinal muscles in front of the bolus widen the tube, resulting in shortening of that part of the food pipe.
e) These rhythmic contractions and relaxations bring in a wave like motion that propels the food bolus into the stomach by the action called peristalsis.
f) Peristalsis brings about the motion of the food all through the alimentary canal with the help of action of different types of muscles involved.
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