914 



THE ORGANS OF VOICE 



the trachea is ridgod transversely l)y the rings, which are rounded on their inner 

 surfaces; hut it is con:iparatively smooth externally, where the outer surfaces of the 

 rings are llattened. 



The first cartilage is l)road, and is occasionally united with the cricoid ahove, 

 or second ring of the trachea helow. 



The last cartilage is likewise broad and strong, and sends a curved beak 

 downwards and backwards at the point of bifurcation of the tracliea. It forms 

 an imperfect ring on each side above the commencement of the corresponding 

 bronchus. 



Two cartilages not uncommonly unite in part, and thus present a bifurcated 

 appearance. 



The fibres of the trachealis are unstripod, and form a transverse layer at the 



Fig. 536.— Anterior View of the Larynx, with the Trachea and Bronchi. 



(Modified from Bourgery.) 



FIRST RING OF TRACHEA 



A rch of aorta 



Jiiflht pulmonary artern 





POSITION OF THYROID ISTHMUS 



LEVEL OF STERNUM 



LAST RING OF TRACHEA 



L'ft jiuliiioiiary artery 

 LEFT BRONCHUS 



posterior flattened part of the tube, wdth an indistinct layer of longitudinal fibres 

 superimposed. 



The yellow elastic fibres, which exist throughout the entire mucous mem- 

 brane, f(jriii a detinite and deep layer at the posterior flattened portion oi the tube. 

 They are gathered into strong longitudinal flattened bands, especially well seen at 

 the lower part of the trachea, and where the fibres separate to ))ass into the 

 bronchi. 



The mucous membrane is smooth and i)inkish in colour; it is i)rovided with 

 numerous glands, especially at its hinder ])art, and is lined by a columnar ciliated 

 e})itheliuni. 



The arteries are derived from the inferior thyroid. 



The veins join the thyroid i)lexuses; and the nerves are supplied by In-anches 

 from the i)neum()gastric, the recurrent laryngeal, and sympathetic. 



I 



