THE (ESOPHAGUS 51 



inclines towards the left side of the windpipe, entering the thorax across 

 the inner aspect of the first rib of the left side. It then regains the 

 upper aspect of the trachea, crosses the base of the heart, and passes 

 through the foramen sinistrum of the diaphragm. Almost immediately 

 upon entering the abdominal cavity it passes through the notch in the 

 upper edge of the lobukis quadratus of the liver, and then opens into 

 the stomach. 



The first part of the cesophagus runs along a groove formed by the 

 inferior surface of the guttural pouches. These, therefore, form its first 

 superior relations. Inferiorly this part is related to the arytenoid and 

 cricoid cartilages, but there are interposed between it and these 

 structures, the posterior crico-arytenoideii and the arytenoideus muscles. 



In the upper half of its course down the neck it is related to the 

 trachea in front or below, and to the longus colli muscle above or 

 behind, whilst laterally it is related to the carotid artery, the pneumo- 

 gastric and sympathetic nerve trunk, and the inferior (recurrent) 

 laryngeal nerve. 



In the lower cervical region it is placed between the left outer 

 surface of the trachea inwardly, and the inner surface of the left inferior 

 scalenus muscle, and also the jugular vein outwardly. 



Its relations in the thorax are not of very great surgical importance, 

 but the opening into the stomach is most peculiar, and should be noted 

 both in connection with the physiological difficulty experienced by the 

 horse in the act of vomiting, and also in connection with the passage 

 of the probang. The fibres surrounding the orifice, as McFadyean 

 describes, are in two sets, namely, a circular set and a set arranged after 

 the manner of a horse-shoe, whilst some of the fibres of the anterior limb 

 of the horse-shoe are derived from the circular fibres. The orifice is thus 

 kept in a state of contraction, and regurgitation from the stomach is 

 frustrated. 



The mucous coat of the oesophagus is quite loosely attached to the 

 outer or muscular coat. 



