C 1228 ) 
What affiftance the Heart receives from the aftion of 
tkc Thorax towards the facilitating its contradtion, with- 
out which affiftance there cou'd ha.ve been -no Syflole, has 
been already (hewn. But . neither the htercofid Mufcles, 
or Diaphragm^ which are fo inftrumental in that part of its 
aftion, can contribute any thing to the Diajlole becaufe 
they ferye only to enlarge the cavity of the Thorax^ and 
thereby to open a iPaflage to the Blood from the Heart, and 
promote its Conftriftion. 
Whatever therefore the Force is, that dilates the Heart, 
and is the Caufe of the Diaftole, it muft be equal to that of 
the Heart, the Intercofid Mufcles and Diaphragm 5 to all 
which it afts as an Antagonift. I take no notice of the 
Serratus Major Anticus^ and other Mufcles, which have an 
obfcure fliare in the Elevation of the Coji^By becaufe as much 
may feafonably be deducted upon the account of the Ob: 
liquHs externffs Abdominis^ and other Mufcles 5 which, hav- 
ing their infertions on fome of the lower Ribs^ are as in- 
ftrumental towards the Deprejjion of em, and fo ballance 
the account. But the chief ufe of thefe is in violent Refpi- 
ration. In ordinary Refpiration their fhare is fmall. 
Such a real f ower ( which may in the leaft be fufpefted 
of any fliare in this Aftion ) is hard, perhaps impoffible to 
be found in the Machine oi any Animal Body j and yet 
without fome fuch Antagonift,it is as impoffible the Circu- 
lation of the Blopd ftiou'd be maintained. All the Engines ^ 
yet difcoyer'd within the Body confpire towards the Con^ " 
ftri&ion oi the Heart, which is the State of ^iefcence^ to 
which it naturally tends. Yet we find it alternately in a 
State of Violence^ that is, of Dilatation 3 and this upon ne- 
ceffity, becaufe upon this Alternation depends all Animal 
Lite. 
Some fufficient Caufe external muft therefore be^ fotind, 
to produce this great Phaenomenpn, which Caufe muft be 
cithe r ia the Air^ or Atmofpberey becaufe wc have no con 
ftantt and immediate Gprnmerce with any other Medims. 
Some 
