THE BRONCHI. 53» 



of the trachea, by contracting the arcs composins; 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 broncld, and in becoming modified in 

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

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

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

 elastic tissue disposed in longitudinal fasciculi, and ad- 

 .,!!lL,fi^,.— _ 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 ' 



FROM THE TRACHEA. postcHor part of thc tube ; they are small, ovoid bodies, 



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



tudinal elastic fibres ; fflands, less in size, are placed between the layers of fibrous 



2, homogeneous surface 1- ... ,i ^-^ , ., ■ -, <• ,i . i 



lavei- of the mucous tissue Uniting the cartilages at the sides ot the trachea, 

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

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



long cells; 5, ciliated ' r / 



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 w4th 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 Beonchi (Figs. 318, 320, 327). 



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

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

 the pulmonary tisaue. 



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 Ivmg, 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 firet 

 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 Steuctuee of the Lungs). 



