STKUCTURE OF THE TRACHEA. 703 





ts of the epiglottis. An elastic band, thyro-epiglottideaniwii^. 

 :nt, connects the lower extremity of the epiglottis to the 

 thyroid cartilage, close to the notch in the upper border of the 

 latter (fig. 247) ; and a membranous layer of fibrous and elastic 

 tissue, hyo-epi>jlottidean ligament, passes between the front of the 

 epiglottis and the hyoid bone. 



STRUCTURE OF THE TRACHEA. The windpipe consists of a series Constitu- 

 of pieces of cartilage, which are deficient behind, and connected 

 together by fibrous tissue. The interval between the cartilages at the 

 back of the tube is closed by fibrous membrane and muscular fibres ; 

 and the interior is lined by mucous membrane with subjacent 

 elastic tissue. 



Cartilages. The pieces of cartilages vary in number from sixteen Cartilages: 

 to twenty. Each forms about three- fourths of a ring, extending form ; 

 round the front and sides of the airtube. Their arrangement is not irregu- 

 quite regular throughout, for some of them are often bifurcated at lanties - 

 one end, or sometimes t\vo adjacent pieces are partly fused together. 

 The highest is commonly broader than the others, and may be 

 joined to the cricoid cartilage. The lowest piece is triradiate, or 

 V-shaped, a median process being sent downwards and backwards 

 in the angle between the two bronchi. 



The fibrous membrane ensheaths the cartilages, and, being con- Fibrous 

 tinued across the intervening spaces, binds them together. It also layer ' 

 extends across the posterior part of the trachea. 



Dissection. On removing the fibrous membrane and the mucous Dissection, 

 glands from the interval between the cartilages at the back of the 

 trachea, the muscular fibres will appear. 



After the muscular fibres have been examined the membranous 

 part of the tube may be divided, to see the elastic tissue and the 

 mucous membrane. 



'liar fibres. Between the ends of the cartilages is a continuous Muscular 

 layer of transverse bundles of unstriated muscle, which is attached kick.* 

 to the truncated ends and the adjacent part of the inner surface of 

 the cartilaginous hoops. By the one surface the fleshy fibres are in 

 contact with the fibrous membrane and glands, and by the other 

 with the elastic tissue. Some longitudinal fibres are superficial to 

 the transverse ; they are arranged in scattered bundles, and are 

 attached to the fibrous tissue. 



The tsue forms a complete lining to the trachea beneath Submucous 



the mucous membrane ; and at the posterior part, where the carti- tissue! 

 lages are wanting, it is gathered into strong longitudinal bundles. 

 This layer is closely connected with the mucous membrane 

 covering it. 



The mucous membrane of the trachea lines the tube, and is Mucous 

 furnished with a columnar ciliated epithelium. eplthemun 



Connected with this membrane are numerous branched mucous an d glands. 

 glands of variable size. The largest are found at the back of the 

 trachea, in the membranous part of the wall, where some are placed 

 outside the fibrous layer, and others between that membrane and 



