THE BRONCHI. 539 



of the trachea, by contracting the arcs composing this 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 the cartilaginous rings, and which, 

 he states, diminish the length of the tube.) 



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

 prolonged, through the medium of the bronchi, and in becoming modified in 

 character, into the air-cells. Its free or superficial surface is perforated by 

 glandular orifices, and exhibits longitudinal ridges which are ineflfacable by dis- 

 tension ; it is lined with ciliated epithelium. Its deep face is covered with yellow 

 elastic tissue disposed in longitudinal fasciculi, and ad- 

 Fig. 319. heres intimately either to the face of the cartilage and 

 " their intermediate ligaments, or to the posterior muscular 

 layer. 



An essential characteristic which distinguishes this 

 membrane from that lining the larynx, is its slight 

 sensibility. 



(The tracheal glands, the orifices of which are so 

 numerous in the mucous membrane, abound towards the 



CILIATED EPITHELIUM . ^ {■ ^^ ^ ^ xi, 11 • 1 1, J • 



FROM THE TRACHEA. postcrior part 01 the tube ; they are small, ovoid bodies, 



3, External layer of longi- lying between the muscular and fibrous coats. Other 



tudinal elastic fibres ; glands, Icss in size, are placed between the layers of fibrous 



fayerofThr'mutus tissuc Uniting the Cartilages at the sides of the trachea, 



membrane ; 3, round Their secretion is poured out upon the free surface of the 



cells ; 4, oval and ob- jj^cous membrane, to lubricate and protect it.) 



long cells: 5, ciliated ^^ , , m, /, , ■ 



cells. Vessels and nerves. — The small arteries emanating 



from the vessels in the vicinity of the trachea — as the 

 carotid and the collateral branches of the brachial arteries — supply it with blood. 

 Its nerves come from the recurrent ; they show small ganglia on their track. 



Functions. — Except as a tube for the passage of the inspired and expired air. 

 the trachea performs no other function. 



3. The Bronchi (Figs. 318, 320, 327). 



Preparation. — After removing the lung from the thoracic cavity, it ie filled with water by 

 fixing the trachea to a water-tap. The bronchi may then be dissected by tearing and triturating 

 the pulmonary tissue. 



Each of the two bronchi — the terminal branches of the trachea — resembles 

 a tree embedded in the substance of the lung, and sending out a multitude of 

 branches. 



Arrangement. — At a short distance from their origin, the bronchi enter the 

 lobes of the lung, and pass backwards and outwards towards the superior part of 

 the base of the organ, giving off in their course large collateral branches, until 

 they themselves are expended. These branches originate alternately above, 

 within, below, and outwards ; and thus extend in every direction. The first 

 forms an obtuse angle with the principal trunk, and is directed forwards, to 

 ramify in the anterior lobe of the lung ; the others are detached at an angle 

 more or less acute. All subdivide into gradually decreasing branches, which 

 soon become of a capillary diameter, and finally open into the infundibula of 

 the pulmonary air-cells (see Structure of the Lungs). 



