DISSECTION OF THE BACK -AMD THORAX. 117 



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 

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

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

 cephalic trunk, 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 (Esophagus. 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 musclar wall of the tube is red, but behind the heart it is pale. 



The Structure of the oesophagus is described at page 154, that of the 

 trachea at page 153. 



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 principal lymphatic vessels of the 

 lungs 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 and lungs. 



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 GlaWd. In the foetus this is a considerable organ, 



