130 ANALYTIC SECT. XVII. 
cccvi. Haller thought the first rib motionless ; 
but this is a manifest error, as, during inspiration, 
all the true ribs, from their attachment to the 
sternum, must join more or less in the common 
motion upwards. 
cccvil. In ordinary inspirations, the intercostal 
muscles alone are employed to raise the ribs; but 
when the breathing is laborious, the muscles of 
the neck, attached to the sternum, clavicles and 
scapule, co-operate materially in the lagen 
of the thoracic cavity. 
ccecvul. When the diaphragm i is ina state of 
expansion, it has a concave appearance when 
viewed from the abdomen; but, in a state of 
contraction, it approximates to a plane. By the 
contraction, or descent of the diaphragm, (as it 
is sometimes called,) the capacity of the thorax 
is enlarged in the direction of the sacrum. 
~ eccrx. As the’ contraction of the intercostal 
muscles and the diaphragm, is simultaneous, all 
pressure is thus suddenly removed from the sur- 
face of the lungs, which suddenly expand, and 
suck into their cells a quantity of air, equal to the 
increased dimension of the thorax. 
cccx. No sooner are the lungs thus inflated, 
than the muscles of inspiration begin to relax ; 
the expansion of the intercostal muscles subjects 
the lungs to pressure, from the whole weight of 
the moving parietes of the thorax; the expanded 
