1146 



SPLANCHNOLOGY 





relation, in front, with the trachea, the left bronchus, the pericardium, and the diaphragm; 

 behind, it rests upon the vertebral column, the Longus colli muscles, the right aortic intercostal 

 arteries, the thoracic duct, and the hemiazygos veins; and below, near the diaphragm, upon 

 the front of the aorta. On its left side, in the superior mediastinum, are the terminal part 

 of the aortic arch, the left subclavian artery, the thoracic duct, and left pleura, while running 

 upward in the angle between it and the trachea is the left recurrent nerve; below, it is in relation 

 with the descending thoracic aorta. On its right side are the right pleura, and the azygos vein 

 which it overlaps. Below the roots of the lungs the vagi descend in close contact with it, the 

 right nerve passing down behind, and the left nerve in front of it; the two nerves uniting to 

 form a plexus around the tube. 



In the lower part of the posterior mediastinum the thoracic duct lies to the right side 

 of the esophagus; higher up, it is placed behind it, and, crossing about the level of the fourth 

 thoracic vertebra, is continued upward on its left side. 



The abdominal portion of the esophagus lies in the 

 ' esophageal groove on the posterior surface of the left 



lobe of the liver. It measures about 1.25 cm. in length, 

 and only its front and left aspects are covered by 

 peritoneum. It is somewhat conical with its base 

 applied to the upper orifice of the stomach, and is 

 known as the antrum cardiacum. 



Structure (Fig. 1033). The esophagus has four 

 coats: an external or fibrous, a muscular, a sub- 

 mucous or areolar, and an internal or mucous coat. 



The muscular coat (tunica muscularis} is composed 

 of two planes of considerable thickness: an external 

 of longitudinal and an internal of circular fibers. 



The longitudinal fibers are arranged, at the com- 

 mencement of the tube, in three fasciculi: one in front, 

 which is attached to the vertical ridge on the posterior 

 surface of the lamina of the cricoid cartilage; and 

 one at either side, which is continuous with the mus- 

 cular fibers of the pharynx: as they descend they blend 

 together, and form a uniform layer, which covers the 

 outer surface of the tube. 



Accessory slips of muscular fibers pass between the 

 esophagus and the left pleura, where the latter covers 

 the thoracic aorta, or the root of the left bronchus, 

 or the back of the pericardium. 



The circular fibers are continuous above with the 

 Constrictor pharyngis inferior; their direction is trans- 

 verse at the upper and lower parts of the tube, but 

 oblique in the intermediate part. 



The muscular fibers in the upper part of the esoph- 

 agus are of a red color, and consist chiefly of the striped 

 variety; but below they consist for the most part of 

 involuntary fibers. 



The areolar or submucous coat (tela submucosa) 

 connects loosely the mucous and muscular coats. It 

 contains bloodvessels, nerves, and mucous glands. 



The mucous coat (tunica mucosa) is thick, of a reddish color above, and pale below. It is 

 disposed in longitudinal folds, which disappear on distension of the tube. Its surface is studded 

 with minute papilke, and it is covered throughout with a thick layer of stratified squamous 

 epithelium. Beneath the mucous membrane, between it and the areolar coat, is a layer of longi- 

 tudinally arranged non-striped muscular fibers. This is the muscularis mucosae. At the com- 

 mencement of the esophagus it is absent, or only represented by a few scattered bundles; lower 

 down it forms a considerable stratum. 



The esophageal glands (glandulas oesophagece) are small compound racemose glands of the 

 mucous type: they are lodged in the submucous tissue, and each opens upon the surface by a 

 long excretory duct. 



Vessels and Nerves. The arteries supplying the esophagus are derived from the inferior 

 thyroid branch of the thyrocervical trunk, from the descending thoracic aorta, from the left 

 gastric branch of the celiac artery, and from the left inferior phrenic of the abdominal aorta. 

 They have for the most part a longitudinal direction. 



The nerves are derived from the vagi and from the sympathetic trunks; they form a plexus, 

 in which are groups of ganglion cells, between the two layers of the muscular coats, and also a 

 second plexus in the submucous tissue. 



FIG. 1033. Section of the human esophagus. 

 (From a drawing by V. Horsley.) Moderately 

 magnified. The section is transverse and from 

 near the middle of the gullet, a. Fibrous cover- 

 ing. 6. Divided fibers of longitudinal muscular 

 coat. c. Transverse muscular fibers, d. Sub- 

 mucous or areolar layer, e. Muscularis mucosse. 

 /. Mucous membrane, with vessels and part of a 

 lymphoid nodule, g. Stratified epithelial lining. 

 h. Mucous gland, i. Gland duct. m'. Striated 

 muscular fibers cut across. 



