24.4 THE OESOrilAGUS. 



ointh dorsal vertebra, and there ends by opening into the cardiac orifice 

 of the stomach. 



Form and position. — 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 narrowest part Ijeing at the commencement 

 behind the cricoid cartilage ; it is also slightly constricted in passing 

 through the diaphragm, but, below that, 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. 



Connections. — In the lower cervical and upper dorsal region the 

 tx'sophagus is applied to the anterior surface of the spine, being con- 

 nected with it and with the longus colli muscle by loose areolar tissue ; 

 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 necJc, the oesophagus lies close behind the 

 trachea, and the recurrent laryngeal nerve ascends on either side in the 

 angle 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 loAver 

 j^art 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 be- 

 tween the two pleura?, comes partially in contact with both of those 

 membranes. 



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

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

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

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

 coat. 



The muscular coat consists of an external longitudinal layer (seen 

 in section in fig. 242, h) and an internal circular layer (r). This twofold 

 arrangement of the muscular fibres prevails throughout the whole length 

 of the alimentary canal ; but the two layers are here much thicker, more 

 uniformly disposed, and more evident than in any other ])art except 

 quite at the lower end of the intestine. The external or lonijihulinal 

 fibres are disposed at the commencement of the tube in three fasciculi, 

 one in front, and one on each side. The lateral fasciculi are blended 

 above with the inferior constrictor of the pharynx ; the anterior fasci- 

 culus arises from the back of the cricoid cartilage at the prominent 

 ridge between the posterior crico-arytenoid muscles, and its fibres 

 spreading out on each side of the gullet as they descend, soon blend 



