THE OESOPHAGUS. 1153 



i fusiform expansion of the tube, of variable length and girth, which lies within the thorax 



i immediately above the point where the gullet is grasped between the two muscular margins 

 of the cBsophageal opening and the diaphragm. It lies in the lowest part of the posterior 

 mediastinum where this is bounded anteriorly by the back of the diaphragm. 



The antrum cardiacum is another name for the abdominal portion of the oesophagus. It is 

 funnel-shaped, and expands towards the stomach. 



Relation of the Aorta to the (Esophagus. The arch of the aorta, passing back to reach 

 the vertebral column, crosses to the left side of the oesophagus ; consequently the descending 

 thoracic aorta lies at first to its left ; lower down, however, as the aorta passes on to the anterior 

 aspect of the vertebral column, and the gullet inclines forwards and to the left, the aorta comes 



to lie posteriorly, and then, as the diaphragm is approached, it lies not only posteriorly, but also 

 somewhat to the right of the oesophagus (Figs. 907 and 908). 



Relation of the Thoracic Duct to the (Esophagus. The thoracic duct, lying to the right 

 of the aorta below, is not directly related to the oesophagus (Fig. 908, E) ; but higher up 

 (Fig. 908, D and E) it lies posterior to it. About the level of the aortic arch the duct passes to 

 the left, and above this (Fig. 908, B and A) will be found on the left side of the oesophagus, and 

 on a plane .somewhat posterior to it. 



Relation of the Pleural Sacs to the (Esophagus. Above the level of the arches of the 

 aorta and of the vena azygos, between which the oesophagus descends, the pleurae, though 

 not lying in immediate contact with the oesophagus, are separated from it only by a little connec- 

 tive tissue, and on the left side also, behind the subclavian artery, by the thoracic duct (Fig. 

 908, B). Here, in thin bodies, the left pleura is very close to the oesophagus, and the thoracic duct, 

 lying on its left side, may occasionally be seen through the pleural membrane. Below the arch 



i of the azygos vein the right pleura clothes the right side of the oesophagus and very often even a 

 considerable portion of its posterior surface too, thus forming a deep recess behind it almost as 

 low down as the opening in the diaphragm. On the left side, below the level of the aortic arch, 

 the left pleura comes in contact with the gullet, only for a short distance, just above the diaphragm 



i (Fig. 908, E). 



Variations. The chief anomalies found in the oesophagus are : (1) Annular or tubular con- 



, strictions ; (2) diverticula, of which the most interesting known as " pressure pouches " are 

 usually situated on the posterior wall close to its junction with the pharynx, and these some- 

 times require surgical interference ; (3) doubling in part of its course ; and (4) communications 

 between the trachea and oesophagus. 



Structure of the (Esophagus (Fig. 911). The cesophageal wall is composed of 

 three proper coats (1) tunica muscularis, (2) tela submucosa, and (3) tunica mucosa. In 

 addition, it is surrounded by an outer covering of areolar tissue (4) tunica adventitia, by 

 i which it is loosely connected to the various structures related to it in its course. 

 This loose covering permits of its free movement and of its increase in size, or of its 

 diminution, during the act of swallowing. 



The tunica muscularis is composed of two layers an outer of longitudinal, 

 'and an inner of circular fibres. The longitudinal layer is highly developed, and, 

 .unlike the condition usually found in the digestive tube, it is as stout as, or in 

 places stouter than, the circular layer. Its fibres form along the greater length of the 

 tube an even covering outside the circular layer, and below they are continued 

 into the longitudinal fibres of the stomach. Above, near the superior end of the 

 oesophagus, the longitudinal fibres of each side, separating at the back, pass round 

 towards the anterior aspect and form two longitudinal bands (Fig. 909), which run up 

 an the front of the tube, and are attached by a tendinous band to the superior part of 

 ;the posterior surface of the cricoid cartilage (Fig. 909). 



The circular muscular fibres, though not forming such a thick layer as the longitudinal 

 fibres, are nevertheless well developed. Below, they are continued into both the circular 

 and oblique fibres of the stomach. Above, they pass into the inferior fibres of the inferior 

 3onstrictor of the pharynx. 



At the superior end of the oesophagus the muscular fibres are entirely of the striated 

 variety. Soon unstriped fibres begin to appear in increasing numbers, and in the inferior 

 half or two-thirds only unstriped muscle is found. 



The longitudinal fibres for about the superior fifth of the tube are entirely striped ; in 

 i the second fifth striped and unstriped are mixed ; whilst in the inferior three-fifths unstriped 

 fibres alone are present. The circular fibres are entirely striated for the first inch ; after 

 this unstriped fibres appear; and in the inferior two- thirds, only unstriped muscle fibres 

 are found. 



The longitudinal fibres are often joined by slips of unstriped muscle, or elastic fibres, 

 which spring from various sources, including the left pleura (m. pleuro-cesophageus, constant, 

 Cunningham), the bronchi (m. broncho-ossophageus), back of trachea, pericardium, aorta, etc. 

 These slips assist in fixing the oesophagus to the surrounding structures in its passage through 

 the thorax, and have been aptly compared to the tendrils of a climbing plant (Treitz). 



The tela submucosa, composed of areolar tissue, is of very considerable thickness, in 



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