THORACIC CAVITY 



97 



thymus, and still more superficially the manubrium sterni 

 with the origins of the attached muscles. 



On the right, it -is in relation with the upper part of the 

 mediastinal surface of the right pleura and lung (Fig. 43), 

 the right vagus nerve, and 

 the arch of the azygos 

 vein (Fig. 12). It is also 

 in relation, on its right 

 side, near its lower end 

 and more anteriorly, with 

 the superior vena cava, 

 and at a higher level with 

 the innominate artery. 



Its left lateral relations 

 are the arch of the aorta 

 below and the left sub- 

 clavian and left common 

 carotid arteries above. 



The Bronchi. Each 

 bronchus passes down- 

 wards and laterally first 

 to the hilus of the corre- 

 sponding lung and thence 

 downwards in the sub- 

 stance of the lung to its 

 lower end. It can, 

 therefore, be divided 

 into an extra-pul- 

 monary and an intra- 

 pulmonary portion. 

 The extra-pulmonary 

 part, like the trachea, 

 is kept permanently 

 open bythe presence 



Thyreoid cartilage 



Crico-thyreoid 



ligament 



Cricoid cartilage 



Part of trachea 

 covered by isthmus 

 of thyreoid gland 



Common carotid 

 artery 



Left subclavian 

 artery 



Aortic arch 



Left bronchus 

 Left pulmonary 

 artery 



First ventral 

 branch of 

 ft bronchus 



Eparterial bi 

 right bronchus 

 Hyparterial branch o 

 right bronchus 

 Right pulmonary artery 



FIG. 49. The Trachea and Bronchi. The dotted 

 line gives the outline of the thyreoid gland. 



of cartilaginous rings 

 in its walls ; and as 

 the rings' are defi- 

 cient posteriorly, the extra-pulmonary part of each bronchus 

 presents a -flattened posterior surface similar to that of the 

 trachea. ^The lumina of the intra-pulmonary parts of the 

 bronchi are kept patent by cartilaginous plates which are 

 irregularly distributed in the substance of the walls. 



VOL. II 7 



