THE (ESOPHAGUS. 821 



back of the fauces between the orifices of the two Eustachian tubes (Kolli- 

 ker). In the part opposite the fauces, the mucous membrane exactly re- 

 sembles that of the mouth. Lower down it becomes paler, and at the back 

 of the larnyx it forms several longitudinal folds or plica;. According to 

 Henle, the epithelium upon the upper portion of the pharynx, as low down 

 as a horizontal line level with the floor of the nares, is columnar and cili- 

 ated ; but, below that point, it is squamous and destitute of cilia. 



THE OESOPHAGUS. 



The oesophagus or gullet, the passage leading from the pharynx to the 

 stomach, commences at the cricoid cartilage opposite the lower border of 

 the fifth cervical vertebra, and, descending along the front of the spine, 

 passes through the diaphragm opposite the ninth dorsal vertebra, and there 

 ends by opening into the cardiac orifice of the stomach. 



The length of the oesophagus is about nine or ten inches. It is of 

 smaller diameter than any other division of the alimentary canal, its nar- 

 rowest part being at the commencement behind the cricoid cartilage ; it is 

 also slightly constricted in passing through the diaphragm, but, below thac, 

 gradually widens into the stomach. The oesophagus is not quite straight in 

 its direction, but presents three slight curvatures, One of these is an antero- 

 posterior flexure, corresponding with that of the vertebral column in the 

 neck and thorax. The other two are slight lateral curves ; for the oesophagus, 

 commencing in the median line, inclines to the left side as it descends to 

 the root of the neck ; thence to the fifth dorsal vertebra it gradually resumes 

 the mesial position ; and finally, it deviates again to the left, at the same 

 time coming forward towards the oesophageal opening of the diaphragm. 

 In the lower cervical and upper dorsal region the oesophagus is applied 

 to the anterior surface of the spine, being connected with it and with 

 the lougus colli muscle by loose areolar tissue ; but between it and the bodies 

 of the upper dorsal vertebrae the thoracic duct ascends obliquely from right 

 to left : its lower third is placed in front of the aorta. In the neck, the 

 oesophagus lies close behind the trachea, and the recurrent laryngeal nerves 

 ascend in the angles between them ; on each side is the common carotid 

 artery, and also a part of the thyroid body, but, as the oesophagus 

 inclines to the left side, it is in more immediate connection with the left 

 carotid. 



In the thorax, the oesophagus is successively covered in front by the 

 lower part of the trachea, by the commencement of the left bronchus, and 

 by the back of the pericardium. The aorta, except near the diaphragm, 

 where the oesophagus is in front of the vessel, lies rather to the left, and 

 the vena azygos to the right ; the pneumogastric nerves descend in close 

 contact with its sides, and form a plexus around it, the left nerve proceeding 

 gradually to the front, and the right nerve retiring behind it. Lastly, the 

 oesophagus, which is here placed in the interval between the two pleurae, 

 comes partially in contact with both of those membranes. 



Structure. The walls of the oesophagus are composed of three coats ; viz., 

 an external or muscular, a middle or areolar, and an internal or mucous 

 coat. Outside the muscular strata, there is a layer of fibrous tissue, with 

 well marked elastic fibres, which is sometimes spoken of as a distinct 

 coat. 



The muscular coat consists of an external longitudinal layer, and an 

 internal circular layer. This twofold arrangement of the muscular fibres 



