484 



DISSECTION OF THE THORAX. 



Superior 

 intercostal 

 vein : 



ending of 

 right, 



and of left. 



Vein from 

 first space. 



(Esophagus 



in the 

 thorax, 



through 

 diaphragm. 



Parts 

 covering it, 



beneath it, 



and on sides, 



Three coats 

 are in it. 



A muscular 

 coat of 



external 

 longitudinal 



the spaces between the superior intercostal above, and the left 

 lower azygos below. It usually receives branches from the fourth 

 to seventh spaces inclusive, and the trunk either joins the lower 

 azygos of its own side, or crosses the spine to open into the right 

 vein. 



The superior intercostal vein is a short trunk which is formed by 

 the union of the veins from the second, third, and, occasionally, 

 from the fourth spaces. On the right side it descends to join the 

 beginning of the arch of the large azygos vein ; but on the left 

 side (tig. 170, i, p. 466) it is directed forwards across the arch of 

 the aorta, and then turns upwards to enter the left innominate vein. 



The highest intercostal vein ascends from the first intercostal space, 

 in company with the superior intercostal artery, and joins the lower 

 end of the vertebral vein. 



The (ESOPHAGUS or gullet (figs. 174 and 175) is a hollow 

 muscular tube, which extends from the pharynx to the stomach, 

 and the thoracic part is now to be examined. 



Appearing in the thorax to the left of the middle line, it is 

 directed beneath the arch of the aorta, and reaches the middle of 

 the spine about the fifth dorsal vertebra. From that spot it is 

 continued through the interpleural space on the right of the aorta, 

 till near the diaphragm, where it takes a position over the aorta, to 

 gain the cesophageal opening. 



As far as the aortic arch the oesophagus lies beneath the trachea, 

 though it projects to the left of the airtube ; beyond the arch it 

 is crossed by the left bronchus, and is thence in contact with the 

 pericardium as far as the diaphragm. At the upper part of the 

 thorax it rests on the longi colli muscles and the vertebrae; but 

 below the arch of the aorta it is separated from the spine by the 

 large azygos vein, the thoracic duct, and the right intercostal arteries, 

 as well as by the aorta near the diaphragm. Laterally it touches 

 the left pleura above the arch, and both pleurae below, but the 

 right much more extensively than the left. Below the bronchus 

 the pneumo-gastric nerves surround the oesophagus with their 

 branches ; and above the same spot the thoracic duct is in contact 

 with it on the left. 



Structure. If a piece of the oesophagus be removed and distended 

 with tow, it will be easy to show a muscular, an areolar, and a 

 mucous coat from without inwards. 



The muscular coat is thick and strong, and consists of two layers 

 of fibres, of which the external is longitudinal, and the internal 

 circular in direction, like the muscular tunic of the other parts of 

 the alimentary tube. In the upper third of the oesophagus the 

 muscular coat is red, and composed of striped fibres ; but below 

 this it becomes gradually paler, and the striped fibres give way to 

 involuntary muscular tissue. 



The external layer is formed of parallel longitudinal fibres, which 

 form a continuous covering, and end below on the stomach. The 

 fibres begin in the neck opposite to the cricoid cartilage ; and at 

 intervals varying from half an inch to an inch and a half, they are 



