THE TRACIIK.l. 4.VJ 



joined in the majority of the rings; they oven overlap in Bomo. These 

 laities are thin and wide, and sometimes bifurcate and unite with the 

 adjoining rings. 



In the middle part of the trachea, these rings are generally larger than 

 at the origin or termination of the tnl>o. The last ring, in serving as a 

 transition between the trachea and bronchi, presents a more complicated 

 arrangement ; being frequently completed by isolated cartilaginous plates, 

 and is always divided by a median spur or bifurcation directed towards the 

 interior of the trachea, into two lateral segments, each of which corresponds 

 to a bronchus. 



Li' laments. The rings of the trachea are united at their borders by 

 intermediate ligaments, which are composed of elastic tissue, and permit the 

 lengthening or shortening of the tube they concur to form. 



Towards the extremities of the arcs, they are confounded with a thin 

 cellular layer that unites these extremities. The first cartilage is received by 

 its anterior border into the cricoid ring, and joined to it by the wide annular 

 ligament mentioned at page 452. Owing to the elasticity of this ligament, 

 the two cartilages it binds together can move one within the other, 

 like two segments of a telescope, and in this way vary the length of tho 

 tube. 



Muscular layer. This layer only covers tho superior face of tho 

 trachea; it is formed of pale, rose-coloured, transverse fasciculi, attached 

 by their extremities to the internal face of the cartilages. Its action 

 undoubtedly diminishes tho diameter of the trachea, by contracting the arcs 

 composing this cartilaginous tube. (Kolliker has found some longitudinal 

 fibres passing across the transverse ones at the posterior part of the trachea. 

 Leyh describes longitudinal fibres in the anterior wall of the trachea, 

 between the mucous membrane and tho cartilaginous rings, and which, ho 

 states, diminish the length of the tube.) 



Mucous membrane. Continuous with that of the larynx, this membrane 

 is prolonged, through tho medium of tho bronchi, and in becoming modified 

 in character, into tho air-cells. Its free or superficial 

 surface is perforated by glandular orifices, and ex- 

 hibits longitudinal ridges which are ineffacablo by 

 distension ; it is lined with ciliated epithelium. Its 

 deep face is covered with yellow elastic tissue dis- 

 I in longitudinal fasciculi, and adheres inti- 

 mately either to tho face of tho cartilages and their 

 intermediate ligaments, or to tho posterior muscular 

 layer. 



An essential characteristic which distinguishes 

 this membrane from that lining tho larynx, is its CM.IATI:I> i:ririu:i,icn 

 slight sensibility. "" "* 



(The tracheal glands, whoso orifices are so numc- ^Sfi* 1 V^- f ;' ngi " 



v . , . . , , , taainal elastic Bores: 



rous in tho mucous membrane, abound towards the ., H omoKencous s ,i r f : ,,.,. 



posterior part of the tube; they are small, ovoid hy.r c.t 7 t!- nun-.. us 

 bodies, lying between the muscular and fibrous coats. membrane; :t, K..iin.l 



Other glands, less in size, are pliuy.l between the '' 1U; 4 > O 1 ""'! "''; 

 .. ,., ,. .., . ,1 long cells; 5, Ciliated 



layers of fibrous tissue uniting tho cartilages at tho ce |j^ 



siil.--; of the trachea. Their secretion is poured out 



lip-in the free surface of tho mucous membrane, to lubricate and protect it.) 

 Vetsrl* <ni, I nerves. Tho small arteries emanating from tho vessels 

 in the vicinity of the trachea as the carotid and tho collateral branches 



