448 THE DIGESTIVE APPARATUS IN MAMMALIA. 



At its entrance into the thoracic cavity, the oesophagus, still deviating to the 

 left, and lying on the side of the trachea, responds, externally, to the inferior 

 cervical gangUon, the afferent and emergent nerves of that ganglion, the ver- 

 tebral arteries and veins, and the superior cervical and dorso-muscular vessels, 

 which obliquely cross its direction. Beyond this it regains its position between 

 the trachea and the longus colli, passes above the left bronchus, to the right of 

 the thoracic aorta, until it reaches between the layers of the posterior mediasti- 

 num, which bring it into relation with the internal face of the limgs ; these are 

 channeled for its reception, and here it is accompanied by the oesophageal artery, 

 and the oesophageal branches of the pneumogastric nerve. 



The very short portion lodged in the abdominal cavity is related, on the 



Fig. 254. 



TRANVERSE VERTICAL SECTION OF HEAD AND NECK IMMEDIATELY IN FRONT OF THE STYLOID 

 PROCESSES, AND BEHIND THE (ESOPHAGUS. 



I, (Esophagus ; 2, inner surface of trachea ; 3, common carotid artery ; 4, recurrent nerve ; 5, 

 thyroid gland; 6, exterior of pharynx; 7, crico-pharyngeus muscle; 8, 9, 10, 11, guttural pouch 

 and objects in its interior ; 12, stylo-pharyngeus muscle ; 13, sphenoid bone ; 14, jugular ganglia; 

 15, internal carotid; 16, 17, pneumogastric nerve; 18, parotid gland; 19, great hypoglossal 

 nerve; 20, jugular vein; 21, subscapulo-hyoideus ; 22, stylo-maxillaris. 



right, to a fissure in the superior border of the Hver, and is enveloped by the 

 peritoneum. It terminates about the upper third of the sixteenth rib. 



Interior. — Internally, the oesophagus presents nothing of interest ; and it 

 only requires to be remarked, that its walls are always shrunken and in contact 

 when food is not passing between them. It appears narrower in consequence of 

 its inflections or relations with other organs : 1. Near its commencement. 2. At 

 its entrance to the thorax. 3. At its passage through the diaphragm. 



Structuee. — The oesophagus has two tunics — a mucous and a muscular. 



The mucous membrane is continuous with that of the pharynx and 

 stomach ; it is white, and shows numerous longitudinal folds, which allow the 



surface of that tube ; in other cases it is drawn to the inferior face, below the sterno-maxillaris 

 muscles, along with the carotid artery and its satellite nerves, the jugular vein maintaining its 

 position. 



