The heart as a muscle, a triangular pyramid, and Mombracco stone
Heart dissections and its auricles; a proof about the pyramid's apex; a white-stone quarry noted 5 January 1511.
The upper right of this page carries Leonardo's pen-and-chalk studies of the dissected heart, which he calls a principal muscle of strength and the most powerful of all the muscles, noting that its auricles act as antechambers receiving blood expelled from the ventricle so that the heart can contract. A pen passage argues geometrically that the three faces of a triangular pyramid can never meet in a single point without destroying the figure. In the left column a red-chalk memorandum, dated 5 January 1511, describes a quarry of white foliated stone at Mombracco near Saluzzo, as hard as porphyry, a slab of which his friend Master Benedetto the sculptor has promised him for grinding colours.
On this page
The auricles as antechambers that let the heart contract
In the relaxed ('extended') heart the muscles running from base to apex, and from apex to top, are to be described. The auricles ('ears') of the heart act as its antechambers, receiving the blood expelled from the ventricle during contraction; without this outflow of part of the blood the heart could not close.
The heart is the most powerful of the muscles
A note beside a contracted heart states that the heart is a principal muscle of strength, the most powerful of all the body's muscles.
The three sides of a triangular pyramid never meet in a point
Leonardo argues that a pyramid on a triangular base can never bring its three faces together at a single point: such a point would have to be divisible, against the geometric definition of a point, and forcing the sides to a point would destroy the triangular figure. He then asks whether dividing the triangle toward infinity ever destroys its figure, concluding that it does not.
A quarry of white foliated stone at Mombracco
Above Saluzzo, at the foot of Monviso, Mombracco holds a quarry of foliated stone as white as unblemished Carrara marble and as hard as porphyry or harder; some pieces held by 'Trottino the drummer' are greyish and very hard.
A slab promised by Master Benedetto, dated 5 January 1511
Leonardo records that his friend Master Benedetto the sculptor has promised to send him a small slab of the Mombracco stone for grinding his colours, dating the note 5 January 1511.