( 1220 ) 
woiald ie juftifiable, without leflening the difficulty. But 
this account I have taken notice of purely for the fake of 
t|xe Calculation, which may be of ufe in the Sequel, the 
account it felf being in other refpe&s more defeftive than 
Dr Lower% to which we v/ill return. 
The Dr, notwithftanding his great Sagacity, appears (to 
me) to have overlcokt (omething of very great moment, 
and importance in the explication of the Aftion of the Heart. 
For, tho it .ju'd be granted, that the M^fcular Fibres oi the 
Heart afted by the Nerves, are the immediate Ihftruments of 
3ts ConfiriUion or Syftole^ yet it muft not be denied, that the 
Iniercofid Mufcles and Diaphragm zxq ot great fervice to 
aid and facihtatethis Contraftion, by opening a Paflage for 
the Blood thro the Lungs, which denied woudbean invin- 
dble obftacle. 
Neither do they promote it that way only. The man- 
ner hov/ they farther aflift, the Heart in its Contraftion, will 
appear manifeftly, if we confider the different Poftqre, Sci- 
tuation and Capacity of the Blood Veffels of the Lungs in 
the feveral times of Ekvation and Deprejpon of the Cofu* 
The Pfilmmry Army rifes from the r%^/ Ventricle of 
the Heart, and runs in one Trunk, till i t comes to, the Afpera 
Arteriay where it is divided, and fends a Branch along with 
each divifion of thQAfperaArteria^^LCCording to all the minuted 
fubdivifions,. of which it is Ijkewife fubdivided, accompany- 
ing all the Br^?/^f^/, in their whole progrefs thro ihe Lungs. 
The Vulr/ionary Vein, which empties it felf into the Left 
Ventricle of the Heart, fpreads it felf on the Afpera Arteria 
and Bronchi, in the fame manner that the Artery docs. . 
The neceflary confequence cf this difpofition is, that this 
Artery and Vein being coextended with, and.faftend to the 
Bro^fchi, mu(\ needs (ufFer fuch alteration of Superficial Di- 
menConSj as the Bronchi do in the Elevation or Deprejfion of 
thcCoJi£. . 
While the Ribs are in a ftate of Dreprefpon (whether * 
before. Commerce with the external Air or after J the Annu^-, 
Idr Cartilages of the Bronchi ^nvik. one into another, and by . 
' ■ that 
