Outlines of human physiology; designed for the use of the higher classes in common schools . Trunk or the Human Skeleton-, a The ster-num or breast bone, b b The spine, c c c c The ribs. a state of relaxation, the centre is considerably elevatedabove the circumference. Between the ribs are situated numerous small mus-cles, which are called intercostals, from their situation,and which are supposed to elevate the ribs. There are other muscles which may be consideredrespiratory muscles, as they have the power of contrib-uting to the enlargement of the cavity of the chest. The lungs are in contact
Outlines of human physiology; designed for the use of the higher classes in common schools . Trunk or the Human Skeleton-, a The ster-num or breast bone, b b The spine, c c c c The ribs. a state of relaxation, the centre is considerably elevatedabove the circumference. Between the ribs are situated numerous small mus-cles, which are called intercostals, from their situation,and which are supposed to elevate the ribs. There are other muscles which may be consideredrespiratory muscles, as they have the power of contrib-uting to the enlargement of the cavity of the chest. The lungs are in contact with the inner side of the 70 RESPIRATION. cavity of the chest. In inspiration this cavity is en-larged, sometimes in one direction principally, and atothers in 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,
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