DISSECTION OF THE BACK AND THORAX. 115 



It is by this channel, also, that the chyle absorbed from the intestine 

 enters the red-blood vessels. The before-mentioned exceptional areas 

 are drained by the right lymphatic duct, a short vessel to be sought 

 afterwards on the right side. 



The Trachea. The thoracic portion of the windpipe is situated in 

 the middle plane of the cavity. Entering between the first pair of ribs, 

 it passes backwards through the anterior mediastinum ; and over the 

 base of the heart it bifurcates to form the right and left bronchi. The 

 angle of bifurcation is under the 6th dorsal vertebra. It is related above 

 to the oesophagus and right longus colli ; and below to the cephalic 

 trimk, arteria innominata, anterior vena cava, and right auricle. On its 

 left side are the arch of the axillary, the thoracic duct, and the arch of 

 the posterior aorta. On the right side it is crossed near its termination 

 by the great vena azygos, as will be seen at a later stage. It is also 

 related to the vagus, recurrent, sympathetic, and cardiac nerves ; and to 

 the prepectoral, tracheal, and bronchial lymphatic glands. 



The ffisoPHAGUS. At the entrance to the chest the gullet lies above 

 the trachea, and a little to its left side ; but as it passes backwards 

 beneath the longus colli muscle, it mounts on to the middle of the 

 upper face of the trachea, and passes directly over its bifurcation, 

 having the arch of the aorta to its left. Beyond that it enters the 

 posterior mediastinum, between whose layers it passes, a few inches 

 below the spine, to perforate the diaphragm by the foramen sinistrum. 

 At its entrance into the chest, and for some distance beyond that point, 

 the muscular wall of the tube is red, but behind the heart it is pale. 



The Structure of the oesophagus is described at page 150,- that of the 

 trachea at page 149. 



Lymphatic Glands of the thorax. The following groups of glands 

 may be seen at this stage : — 



1. (Esophageal glands of small size, along the oesophagus, between the 

 layers of the posterior mediastinum. 



2. Bronchial glands, situated at the bifurcation of the trachea, and 

 extending along the bronchi. The lymphatic vessels of the lung join 

 these. 



3. Tracheal or Cardiac glands, a double chain of glands on the lower 

 face of the trachea, in the anterior mediastinum, and placed on the 

 course of the lymphatic vessels from the heart. 



4. A series of small glands beneath the pleura, at the upper 

 •extremities of the intercostal spaces. 



5. Prepectoral glands. — These belong to the neck rather than to the 

 thorax, but some of them may have been left by the dissector of the 

 former region. They are situated at the entrance to the chest, beneath 

 the great vessels. 



The Thymus Gland. In the foetus this is a considerable organ. 



