CH. XXIV.] 



THE PLEURA. 



343 



layers arc, in health, everywhere in contact one with the other ; 

 and between them is only just so much fluid as will ensure the 



Fig. ',!.) Ciliated epithelium of the human trachea, a, layer of longitudinally arranged 

 elastic fibres ; ft, basement membrane ; c, deepest c ills, circular in form ; </, inter- 

 mediate elongated cells ; t, outermost layer of cells fully developed and bearing cilia. 

 x 350. (Kolliker.) 



gliding easily, in their expansion and contraction, on the 

 inner surface of the parietal layer, which lines the chest-wall. 



If, however, an opening is 

 made so as to permit air or fluid 

 to enter the pleural sac, the 

 lung, in virtue of its elasticity, 

 recoils, and a considerable space 



Pig. 314. Terminal branch of a brotu-binl 

 tube, with its infundibula and aii 

 from the margin of the lung of a monkey, 

 injected with 'inn k-ih'-i . /. tormina! 

 bronchial twig ; b ft, infundibula and air- 

 MM. X 10. (F. . Schulze.) 



F>K- 3>5- Two small infundibula or 

 groups of air-sacs, a >>. with air-sacs, 

 ft ft, and the ultimate bronchial tube*, 

 c c, with which the air-sacs commu- 

 nicate. From a new-born child. 



(Kolliker.) 



is left between it and the chest-wall. In other words, the natural 

 elasticity of the lungs would cause them at all times to contract 

 away from the ribs were it not that the contraction IB resisted by 

 atmospheric pressure which bears only on the inner surface of 



