THE (ESOPHAGUS. 953 



the thyroid gland and thoracic duct ; behind, it rests upon \he vertebral column 

 and Longi colli muscles; on each side, it is in relation with the common carotid 

 artery (especially the left, as it inclines to that side) and part of the lateral lobes 

 of the thyroid gland: the recurrent laryngeal nerves ascend between it and the 

 trachea. 



In the thorax it is at first situated a little to the left of the median line ; it then 

 passes behind the left side of the aortic arch, and descends in the posterior 

 mediastinum, along the right side of the aorta, nearly to the Diaphragm, where 

 it passes in front and a little to the left of the artery, previous to entering the 

 abdomen. It is in relation, in front, with the trachea, the arch of the aorta, 

 left carotid, and left subclavian arteries, the left- bronchus, and the posterior 

 surface of the pericardium ; behind, it rests upon the vertebral column, the Longi 

 colli muscles, the thoracic duct (opposite middle dorsal vertebrae), the right inter- 

 costal vessels, and below, near the Diaphragm, upon the front of the aorta : 

 lateral.?'/, it is covered by the pleurae : the vena azygos major lies on the right 

 and the descending aorta on the left side. The pneumogastric nerves descend in 

 close contact with it on each side; lower down the right nerve passes behind, and 

 the left nerve in front of it. 



Structure. The oesophagus has three coats an external or muscular; a 

 middle or areolar ; and an internal or mucous coat. 



The muscular coat is composed of two planes of fibres of considerable thickness, 

 an external longitudinal and an internal circular. 



The longitudinal fibres are arranged, at the commencement of the tube, in three 

 fasciculi : one in front, which is attached to the vertical ridge on the posterior 

 surface of the cricoid cartilage ; and one at each side, which is continuous with 

 the fibres of the Inferior constrictor : as they descend they blend together and 

 form a uniform layer, which covers the outer surface of the tube. 



Accessory slips of muscular fibres are described by Dr. Cunningham as 

 passing between the oesophagus and the pleura, where it covers the thoracic 

 aorta (almost always), or the root of the left bronchus (usually), or the back of 

 the pericardium or corner of the mediastinum (more rarely), as well as other still 

 more rare accessory fibres. In Fig. 572, taken from a dissection in the Museum 

 of the Royal College of Surgeons, several of these accessory slips may be seen 

 passing from the oesophagus to the pleura, and two slips to the back of the trachea 

 just above its bifurcation. 



The circular fibres are continuous above with the Inferior constrictor; their 

 direction is transverse at the upper and lower parts of the tube, but oblique in the 

 central part. 



The muscular fibres in the upper part of the oesophagus are of a red color, and 

 consist chiefly of the striped variety, but below they consist for the most part of 

 involuntary muscular fibre. 



The areolar coat connects loosely the mucous and muscular coats. 



The mucous coat 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 papillae, and it is covered throughout with a thick 

 layer of stratified pavement epithelium. Beneath the mucous membrane, between 

 it and the are :>lar coat, is a layer of longitudinally arranged non-striped 

 muscular fibres. This is the muscularis mucosw. At the commencement it is 

 absent, or only represented by a few scattered bundles ; lower down it forms a 

 considerable stratum. 



The aesophageal glands are numerous small compound racemose glands 

 scattered throughout the tube ; they are lodged in the submucous tissue, and open 

 upon the surface by a long excretory duct. They are most numerous at the lower 

 part of the tube, where they form a ring round the cardiac orifice. 



Vessels of the (Esophagus. The arteries supplying the oesophagus are de- 

 rived from the inferior thyroid branch of the thyroid axis of the subclavian. 

 from the descending thoracic aorta, and from the 'gastric branch of the coeliac 



