Outlines of human physiology; designed for the use of the higher classes in common schools . The Diaphragm during expiration, a Itstendinous centre, h b Its fleshy c The lateral cavities of the chest inwhich the lungs lie. Ordinary inspiration may be accomplished by the iaction of the diaphragm alone. The contraction of this imuscle necessarily depresses its centre, which was be- ;fore elevated towards the lungs. The instant this takes j RESPIRATION. 71 place, the air rushes into the lungs through the wind-pipe, and thus prevents a vacuum, which would other-wise be produced between the
Outlines of human physiology; designed for the use of the higher classes in common schools . The Diaphragm during expiration, a Itstendinous centre, h b Its fleshy c The lateral cavities of the chest inwhich the lungs lie. Ordinary inspiration may be accomplished by the iaction of the diaphragm alone. The contraction of this imuscle necessarily depresses its centre, which was be- ;fore elevated towards the lungs. The instant this takes j RESPIRATION. 71 place, the air rushes into the lungs through the wind-pipe, and thus prevents a vacuum, which would other-wise be produced between the chest and the lungs,In every inspiration, the ribs are somewhat raised,. The Lungs of Man. a The heart, b b The Lungs,c c The Diaphragm. though ordinarily in a very slight and almost impercep-tible degree* In a full inspiration, there is an evident elevation ofthe ribs, and in a forced inspiration, this elevation ismuch greater ; the cavity of the chest being in bothcases much more enlarged than in an ordinary inspira-tion. This enlargement of the chest by the elevation ofthe ribs, is owing to the oblique direction in which the 72 RESPIRATION. ribs are placed ; so that when they are raised up, theyare also turned outwards, and the cavity of the chest isconsequently much enlarged. The ribs are elevated in inspiration by the contrac-tion of certain muscles. It was the opinion of Hallerthat this elevation was produced by the intercostal mus-cles, those muscles that are situated between the supposed that the first rib was immoveable, andserved as a fixed point, and that the contraction of themuscles that arose from it, raised the next rib, and thatin t
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