(ESOPHAGUS. 839 



or four branches, the trunk either joins the lower azygos of its own side, 

 or crosses the spine to open into the right vein. 



The (ESOPHAGUS or gullet is a hollow muscular tube, which extends 

 from the pharynx to the stomach : the cervical portion has been described 

 at p. 121, and the thoracic part is now to be examined. 



Appearing in the thorax rather to the left of the middle line, the gullet 

 is directed beneath the arch of the aorta, and reaches the middle of the 

 spine about the fifth dorsal vertebra. From that spot it is continued 

 through the interpleural space on the right of the aorta, till near the 

 diaphragm, where it takes a position over the aorta, to gain the oesopha- 

 geal opening of that muscle. 



As far as the aortic arch the oesophagus lies beneath the trachea, though 

 it is inclined somewhat to the left of the air tube ; beyond the arch it is 

 crossed by the left bronchus, and is concealed by the pericardium as far 

 as the diaphragm. At the upper part of the thorax the gullet rests on 

 the longus colli muscle and the vertebrae ; but below the arch of the aorta 

 it is separated from the spine by the intercostal vessels, and the aorta. 

 Laterally it touches the left pleura above the arch, and both pleurae be- 

 low, but more of the right than the left. Below the bronchus the pneu- 

 mogastric nerves surround the oesophagus with their branches ; and above 

 the same spot the thoracic duct is in contact with it on the left. 



Structure. If a piece of the gullet be removed and distended with tow, 

 it will be easy to show a muscular, fibrous, and mucous coat, one within 

 another. 



The muscular coat is thick and strong, and possesses two layers of fibres, 

 of which the external is longitudinal, and the internal circular in direc- 

 tion, like the muscular tunic of the other parts of the alimentary tube. 

 In the upper third of the oesophagus the fibres are red, but below that spot 

 the color becomes paler. 



The external layer is formed of parallel longitudinal fibres, which form 

 an entire covering, and end below on the stomach. The fibres begin 

 opposite the cricoid cartilage (p. 131) ; and at intervals varying from half 

 an inch to an inch and a half, they are connected with tendinous points 

 (sV to iV of an inch long) like the fibres of the rectus abdominis muscle. 



The internal layer of circular fibres is continuous above with the fibres 

 of the pharynx ; they are more oblique at the middle than at either end 

 of the oesophagus. 



The fibrous layer is situate between the muscular and mucous coats, 

 and attaches the one to the other loosely. 



The mucous coat will be seen on cutting open the tube : it is reddish in 

 color above but pale below, and is very loosely connected with the muscu- 

 lar coat, so that it is thrown into longitudinal folds when the oesophagus is 

 contracted. Lining the interior is a thick layer of scaly epithelium ; and 

 the surface is studded with minute papillae. 



Some compound glands (cesophageal) are scattered along the tube ; at 

 the lower part of the gullet they are most numerous, and form a ring 

 (cardiac) close to the stomach. 



LYMPHATICS OF THE THORAX. In the thorax are lymphatic vessels 

 of the wall and the viscera, which enter collections of glands, and end in 

 one or other of the two lymphatic ducts. Besides these, the large thoracic 

 duct traverses the thorax in its course from the abdomen to the neck. 



Lymphatic glands. Along the course of the internal mammary artery 

 lies a chain of sternal or mediastinal glands, which receive lymphatics 



