E 3 
Fibres, that form the Septum and Initde of the Left 
Ventricle, it fhortens the Length of the Heart, or , 
draws the Apex up nearer to the Bafe: This is done 
without any Contrariety in the ACtion of thefe Fibres, 
or deftroying the Force of each other 5 but, on the 
contrary, they being all parallel to each other, and a 
Continuation of the fame Fibres, do afli ft each other 
in their ACtion. 
The Dodtor fuppofes this Contraction is not caufed 
fo much by the Influx of the nervous Spirits, as by 
the Influx of the arterial Blood, through the Coro- 
nary Arteries into the Subftance of the Heart ; and 
that the Contraction of the Auricles comes from the 
fame Caufe; which will be alternate with that of 
the Heart, becaufe the lateral Branches, which arife 
out of the Trunk of the Coronary Artery, that en- 
compafles the Bafe of the Heart and both Auricles, 
are on one Side diflributed into the Subftance 
of the Heart, and on the other Side into the Coat 
of the Auricles 5 and will be alternately comprefled, 
and alternately free, as the Auricles and Ventricles 
are alternately full or empty of Blood. 
I hope you will excufe the Imperfections of this 
fhort Account; and that our Brethren will accept it 
as a Mark of my Refpedt, and that it may fatisfy their 
Curiofity for the prelent, till the Doctor’s Account at 
large fhall be publifhed. I am, 
London, Aug. 7 . SIR, 
To W m . Bogdani,E/7i 
<&c . [then 3 at Sp.il- 
dmg. 
Tour mofi obliged, 
Humble Servant, 
C. Mortimer. 
V. 4 
