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The alimentary canal is a tube beginning at the mouth and passing through the body to the anus. It is primarily used for the reception of food.
 Research Alimentary canal
A notochord is an axial stiffening rod extending along the length of an animal and lying immediately above the alimentary canal.
Research Notochord
The pharynx is a region of the alimentary canal following the buccal cavity.
Research Pharynx
The oesophagus is the region of the alimentary canal following the pharynx. The walls of the
oesophagus are muscular and force food along by contractions. The oesophagus is composed of a thick muscle wall which is voluntary (striped) muscle in the upper part, and involuntary (smooth) muscle in the lower part. The oesophagus ends byjoining the cardiac orifice of the stomach a little less than four cm below the diaphragm. It therefore has three parts. The cervical portion in the lower part of the neck lies immediately behind the trachea with lobes of the thyroid on either side. The thoracic portion lies, in the upper part, close to the back of the trachea in front of the vertebral column. In the lower part the oesophagus passes a little to the left and is crossed by the left bronchus, later .lying immediately behind the pericardium until it pierces the diaphragm.
Except during the passage of food, the oesophagus is flattened like a muscle strap but can distend to 25 mm in diameter. With the exception of the pylorus it is the narrowest portion of the alimentary tract and the oesophagus itself has three constrictions where it becomes narrower than in the rest of its course. The first is at the upper end behind the cricoid cartilage; the second is at the level of the bifurcation of the trachea into right and left bronchus; while the third narrow point is where the oesophagus passes through the diaphragm. Unlike the abdominal parts of the alimentary tract, there is no peritoneal coat on the thoracic and cervical
oesophagus.
Research Oesophagus
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The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
©1993 - 2009 The Probert Encyclopaedia
Southampton, United Kingdom
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Abbreviations
