722 ORGANS OF DIGESTION. 



petrous portion of the temporal bones. As it descends, it diminishes in thick, 

 ness, and is gradually lost. 



The mucous coat is continuous with that lining the Bustachian tubes,the nares, 

 the mouth, and the larynx. It is covered by columnar ciliated epithelium, as 

 low down as on a level with the floor of the nares ; below that point, it is of the 

 squamous variety. 



The muscular coat has been already described (p. 340). 



The pharyngeal glands are of two kinds: the simple, or compound follicular, 

 which are found in considerable numbers beneath the mucous membrane, 

 throughout the entire pharynx ; and the racemose, which are especially nume- 

 rous at the upper part of the pharynx, and form a thick layer, across the back 

 of the fauces, between the two Eustachian tubes. 



THE (ESOPHAGUS. 



The (Esophagus is a membranous canal, about nine inches in length, extending 

 from the pharynx to the stomach. It commences at the lower border of the 

 cricoid cartilage, opposite the fifth cervical vertebra, descends along the front 

 of the spine, through the posterior mediastinum, passes through the diaphragm, 

 and, entering the abdomen, terminates at the cardiac orifice of the stomach, 

 opposite the ninth dorsal vertebra. The general direction of the oesophagus is 

 vertical ; but it presents two or three slight curvatures in its course. At its 

 commencement, it is placed in the median line ; but it inclines to the left side 

 as far as the root of the neck, gradually passes to the middle line again, and, 

 finally, again deviates to the left, as it passes forward to the cesophageal open- 

 ing of the Diaphragm. The oesophagus also presents an. antero-posterior flex- 

 ure, corresponding to the curvature of the cervical and thoracic portions of the 

 spine. It is the narrowest part of the alimentary canal, being most contracted 

 at its commencement, and at the point where it passes through the Diaphragm. 



Relations. In the neck, the oesophagus is in relation, in front, with the trachea ; 

 and, at the lower part of the neck, where it projects to the left side, with the 

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

 and Long us Colli muscle ; 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 across the left side of the transverse part 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, the left bronchus, and the posterior surface of the peri- 

 cardium ; behind, it rests upon the vertebral column, the Longus Colli, and the 

 intercostal vessels ; and below, near the Diaphragm, upon the front of the aorta; 

 laterally, it is covered by the pleura ; 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, the right nerve passing down behind, and the left nerve 

 in front of it. 



Surgical Anatomy. The relations of the oesophagus are of considerable practical interest to 

 the surgeon, as he is frequently required, in cases of stricture of this tube, to dilate the canal 

 by a bougie, when it becomes of importance that the direction of the oesophagus, and its rela- 

 tions to surrounding parts, should be remembered. In cases of malignant disease of the oeso- 

 phagus, where its tissues have become softened from infiltration of the morbid deposit, the 

 greatest care is requisite in directing the bougie through the strictured part, as a false passage 

 may easily be made, and the instrument may pass into the mediastinum, or into one or the other 

 pleural cavity, or even into the pericardium. 



The student should also remember that contraction of the oesophagus, and consequent 

 symptoms of stricture, are occasionally produced by an aneurism of some part of the aorta 

 pressing upon this tube. In such a case, the passage of a bougie could only hasten the fatal 

 issue. 



