‘ " 1908. | Study of the Mechamsm of Respiration, ete. L87 
lower lung margin glides downwards in inspiration and insinuates itself 
between them. As the lung recedes the surfaces again come together. The 
diaphragmatic pleura, owing to its elasticity, accommodates itself to con- 
traction of the diaphragmatic circumferential muscle-fibres, and its smooth 
surface allows it to glide easily over the apposed costal layer, which is fixed in 
such wise that it cannot be displaced. Owing to negative intra-pleural 
suction and positive intra-abdominal pressure, together with molecular 
cohesion of the lubricated pleural surfaces, the pleural union thus formed is 
of sufficient strength to bind the diaphragm during its action closely to the 
chest-wall, and, moreover, is of mechanical advantage to the diaphragm, since: 
in function it resembles the band or loop through which a muscle acts in: 
order to change the direction of its line of force, 
VOL. LXXX.—B. Q 
