The esophagus is a muscular tube about 25 centimeters in length which is immediately continuous with the lower portion of the pharynx above and with the cardiac portion of the stomach below. It consists of three portions of the cervical, the thoracic, and the abdominal. The thoracic portion is by far the longest, while the abdominal is very short.
The cervical portion is continuous with the pharynx at the level of the sixth cervical vertebra or at the disc between the sixth and seventh vertebrae, this point likewise marking the boundary between the trachea and the larynx. As the pharynx is exactly behind the larynx, so the esophagus is at first directly posterior to the trachea and immediately in front of the cervical vertebrae and the long cervical muscles, being separated from the latter by the deep layer of the cervical fascia (prevertebral fascia) and by loose connective tissue.
It has in general an almost vertical direction, but even at the beginning it shows a slight tendency to deviate toward the left, so that the lower part of the cervical portion projects to the left somewhat beyond the trachea. This deviation is slight in the cervical region but becomes greater in the thoracic portion of the organ, which extends from the superior thoracic aperture to the esophageal opening in the diaphragm, and is situated in the posterior mediastinum.
Unlike the cervical portion, the thoracic esophagus is not placed immediately in front of the vertebrae, but is separated in its lower portion from these structures by the aorta. It maintains throughout the thorax its general vertical direction, following, however, the curvature of the thoracic vertebrae in its upper portion. The beginning of it is near the anterior surface of the vertebral column and approximately in the median line, and at the tracheal bifurcation the greater portion of the viscus is behind the left bronchus, while below this point it is in contact with the posterior wall of the pericardium. In the latter situation it is still near the middle line, and for a short distance pursues a course almost parallel with the descending aorta which is situated to the left, but in its further course the esophagus passes to the left and in front of the aorta, the latter structure displacing it more and more from the median line and from the anterior surface of the vertebral column. In this manner the esophagus crosses the aorta at an acute angle and takes a position in front of the latter and markedly to the left of the median line.
The upper portion of the thoracic esophagus is in relation upon the right with the vena azygos and posteriorly with the thoracic duct. The pneumogastric nerves also lie immediately upon the esophagus.
The esophagus enters the esophageal opening in the diaphragm at the level of the ninth thoracic vertebra, the length of the opening corresponding to the width of a vertebral body. At its passage through the diaphragm it has already taken up its position well to the left of the median line, which is practically occupied by the aorta.
The abdominal portion of the esophagus is about 1 centimeter long. It passes from the diaphragm rather suddenly to the left and empties into the stomach at the level of the eleventh thoracic vertebra.
The esophagus is not of uniform caliber throughout, but exhibits a variable number of constrictions with intervening fusiform dilatations. It is especially narrow at its commencement, at its passage through the diaphragm and frequently where it crosses the left bronchus. Its wall gradually diminishes in thickness from above downward owing to the replacement of the striated by the non striated musculature, and in the empty state of the organ the mucous membrane is arranged in marked longitudinal folds and the lumen is quite small. In the dead subject both the esophagus and its lumen are usually markedly flattened from before backward. The distinct submucosa contains small mucous esophageal glands, and the muscular tunic is composed of an inner layer of circular and of an outer layer of longitudinal fibers, the fasciculi of the longitudinal fibers appearing as fine longitudinal stripes upon the outer surface of the viscus.
In its course through the posterior mediastinum the musculature is reinforced by fasciculi which originate from the mediastinal pleura (m. pleuroesophagus) and from the wall of the left bronchus (m. bronchoesophagus).
Human Anatomy (1909) by DR. Johannes Sobotta (1869-1945) Professor of Anatomy in the university of Wurzburg.