THE TRACHEA. 



537 



After clearing the two first ribs, where it reaches its thoracic portion, the 

 trachea responds, superiorly, to the longus colli and the oesophagus ; below to 

 the brachial vessels, the anterior aorta which furnishes them, the anterior vena 

 cava, the cardiac and recurrent nerves, and to the base of the heart ; laterally, 

 to the inferior cervical ganglia of the great sympathetic, the vertebral vessels — 

 cervical and dorso-muscular — and to the two layers of the anterior mediastinum ; 



Fig. 317. 



THE RESPIRATORY ORGANS (INFERIOR, OR FRONT VIEW). 



1, Trachea; 2, jugular vein; 3, rectus anticus major; 4, carotid artery ; 5, longus colli; 6, origin 

 of the common carotids; 7, vertebral artery; 8, section of first rib; 9, cephalic trunk of right 

 axillary artery; 10, anterior lobe of right lung; 11, middle, or supplementary lobe of ditto; 12, 

 posterior portion or lobe of ditto ; 13, heart; 14, cardiac artery ; 15, ventricular branch of cardiac 

 vein; 16, oesophagus. 



to the right, the vena azygos ; to the left, the arch of the aorta and the thoracic 

 duct. The latter is sometimes carried to the opposite side. 



Steuctuee. — The trachea comprises in its structure : the cartilaginous rings 

 which form its base ; the ligaments which unite these rings ; the mucous mem- 

 hrane spread over its inner face ; a muscular layer, which only lines that mem- 

 brane superiorly ; and vessels and nerves. 



Cartilaginous rings of the trachea. — These are about fifty in number, and do 



