C *7? 1 
other, run inwards, and then, riling up again towards 
the Bafe, form that Side of the Septum which con- 
ftitutesPart of the Infide of the Right Ventricle ; and 
like wife form the Column <e carnet of the Right Ven- 
tricle: The Fibres of the interiour Courfe of the Left 
Ventricle dccuflate and form in the fame manner the 
internal Fibres and Column £ carnea of the lame Ven- 
tricle: The external Courfe of Fibres of the Left 
Ventricle are only a Continuation of thofe of the 
Right Ventricle, which together embrace the Heart 
circularly, while -the internal Courfe of Fibres of the 
Left Ventricle run chiefly from the Apex towards the 
Bafe, fo that on the Left Side of the Ventricle they 
crofs the external Courfe nearly at Right Angles; but 
on the Side of that Ventricle which forms the Septum , 
they run from the Apex towards the Bafe, in the fame 
Direction as on that Side of the Septum which is next 
to the Right Ventricle. 
The feveral Courfes of the Fibres may be eafily traced 
in h boiled Heart j and if they are not found to anfwer to 
the Directions of the Lines on the Paper- cone with the 
ftriCteft mathematical Exa&nefs, when rolled up as at 
Fig. 3 . you mud conlider, that the Form of the Heart 
is not exactly conic, though neareft reducible to that 
Figure ; and moreover that the Bafe is not a Plane as 
in the Paper-cone, but of a convex round Form ; 
and the tendinous Circle round it is of a fmaller 
Diameter than the Middle Part of the Heart. 
By this Structure and Circumvolution of the Fibres, 
the Mufcle which conftitutes the Heart, doth, by a 
Ample Contraction of its Length, by thofe external 
Fibres, which encompafs both Ventricles, contract 
the Diameter of the Heart, while by the internal 
T 1 1 1 2 Fibres, 
