1140 



DIGESTIVE SYSTEM 



mediastinum it has anteriorly the pericardium, which separates it from the left 

 atrium and a portion of the diaphragm; posteriorly it rests upon the vertebral 

 column, accessory hemiazygos and hemiazygos veins, the right aortic intercostal 

 arteries, the thoracic duct, and the descending aorta. To the right is the right 

 pleural sac, the vena azA^gos, which it partly overlaps, and below, the thoracic 

 duct. To the left in the upper part is the descending thoracic aorta, and, 

 below, the left pleural sac is separated from it by a little loose areolar tissue. 

 It is surrounded by the oesophageal plexus formed by the vagi nerves, and, as 

 they emerge from the lower part of the plexus, the left vagus lies in front of the 

 oesophagus and the right vagus behind. 



Fig. 896. — Cross-sections Illustrating the Relations of the (Esophagus at Various 



Levels. 



eura 



oesophagus 



B 



)racic 

 centrum /// /]g£^ 

 pleura 



left 

 pleura 



4 



I 



D 



Abdominal portion. — The oesophagus lies in the epigastric region of the abdo- 

 men. Anteriorly is the left lobe of the liver. To the left the left lobe of the liver 

 and the fundus of the stomach. To the right the caudate (Spigelian) lobe of the 

 liver, and posteriorly the decussating fibres of the crura of the diaphragm and the 

 left inf(!rior phrenic artery. The abdominal portion is very short, usuallj^ not 

 more than 2 cm. (4/5 inclij in length (see figs. 896 D, 907). 



Structure. — The thick-walled asophagus presents the four typical tunics of the alimentary 

 canal (fiR. H97). The mucosa and the muscularis are the most important, the suhmucosa and 

 the external adventitia being accessory layers. The mucosa (fig. 897) is thick and strong, of 

 reddish colour in its upper portion and more greyish below. It presents deep longitudinal folds 

 to allow for distention, and when empty the lumen is therefore stellate in cross sections. The 

 lining epithelium is stratified squamous. The lamina propria presents numerous papillae, 

 and is limited externally by a muscularis mucosce. This is a comparatively thick layer (except 

 at the upper end) and is composed of smooth muscle fibres, longitudinally arranged. 



