278 



THE CIRCULATION. 



fibres, while the dotted line shows the narrowed and elongated 

 figure necessarily produced by their contraction. This phenomenon, 



therefore, of the protrusion of the apex 

 Fig. 90. of the heart at the time of contraction, is 



not only fully established by observation, 

 but is readily explained by the anatomical 

 structure of the organ. 



3. Simultaneously with the hardening 

 and elongation of the heart, its apex moves 

 slightly from left to right, and rotates also 

 upon its own axis in the same direction. 

 Both these movements result from the 

 peculiar spiral arrangement of the cardiac 

 fibres. If we refer again to the preceding 

 Diagram of CIRCULAR FIBRES diagrams, we shall see that, provided the 



OF THE HEAKT.aud their con- , ,..,,.,. 



traction. fibres were arranged in simple longitudi- 



nal loops (Fig. 87), their contraction would 



merely have the effect of drawing the point of the heart directly 

 upward in a straight line toward its base. On the other hand, if 

 they were arranged altogether in a circular direction (Fig. 90), 

 the apex would be simply protruded, also in a direct line, 

 without deviating or twisting either to the 

 Fig. 91. right or to the left. But in point of fact, 



the superficial fibres, as we have already 

 described, run spirally, and, curling round 

 the point of the heart, turn inward toward 

 its base ; so that if the apex of the organ be 

 viewed externally, it will be seen that the 

 superficial fibres converge toward its cen- 

 tral point in curved lines, as in Fig. 91. It 

 is well known that every curved muscular 

 fibre, at the time of its shortening, necessa- 

 rily approximates more or less to a straight 



line. Its curvature is diminished in exact proportion to the extent 

 of its contraction ; and if arranged in a spiral form, its contraction 

 tends in the same degree to untwist the spiral. During the con- 

 traction of the heart, therefore, its apex rotates on its own axis in 

 the direction indicated by the arrows in Fig. 91, viz., from left to 

 right anteriorly, and from right to left posteriorly. This produces 

 a twisting movement of the apex in the above direction, which is 



CONVERGING FIBRKSJIT 

 THE APEX OF THE HEART. 



