upon the account of the Obliquus externus Abdominis , and other Muscles; which having their Insertions on some of the lower Ribs are as instrumental towards the Depression of them, and so balance the Account. But the chief use of these is in violent Respiration: In ordinary Respiration their share is small.
Such a real Power (which may in the least be suspected of any share in this Action) is hard, perhaps impossible to be found in the Machine of any Animal Body; and yet without some such Antagonist, it is as impossible the Circulation of the Blood should be maintain'd. All the Engines yet discover'd within the Body, conspire towards the Constriction of the Heart, which is the State of Quiescence, to which it naturally tends. Yet we find it alternately in a State of Violence, that is, of Dilatation; and this upon necessity, because upon this Alternation depends all Animal Life.
Some sufficient Cause External must therefore be found, to produce this great Phænomenon ; which