4. =Section of the Heart.= The heart may be examined either in the body or outside. The choice of several methods may be taken, and the one most convenient and easy of performance is advised, rather than a method based upon such considerations as the direction of the blood-current in the normal body. The chief essential is to expose completely the interior of the heart with the least possible disturbance of anatomic relationships, and to accomplish this in the simplest and easiest way. Such a method must leave the heart in such shape that it can be reconstructed for histologic study or utilized as a museum specimen. This can be accomplished by a modified _Rokitansky_ method, as follows: The heart is first carefully inspected as it lies in the pericardial sac. The apex is then lifted in the left hand and the posterior wall inspected. The heart is then drawn up over the right edge of the ribs, so that the left border of the heart presents uppermost as the line of greatest convexity. The point of the narrow brain-knife (amputation-knife), with cutting edge upward, is then inserted through the wall of the left ventricle at the apex, just to the left of the septum, and the knife pushed into the cavity until the point can be forced through the ventricular wall just below (ventricular side) the left auriculoventricular ring, and the ventricle-wall is then cut upward (as the heart is held) to the apex, in the line of greatest convexity, exposing the cavity of the left ventricle. The knife is laid aside and the ventricle is explored with the fingers of the right hand and the size of the mitral opening estimated. Before the fingers are introduced through the valvular openings the flaps should be carefully examined to see that no vegetations, thrombi, etc., are in danger of being loosened by them. With the opening of the heart-chambers the blood, if fluid, may pour out into the pericardial sac and flood the pleural cavity if not prevented by sponging or by removing it by means of a beaker. The knife is then introduced on the flat through the mitral opening into the left auricle in a line continuing the first incision with the junction of the left pulmonary veins. (See Fig. 38.) The knife is then turned with cutting-edge upward, the point thrust through the upper left pulmonary vein or between the left pulmonary veins, and the auricular wall is cut upward (downward anatomically) to meet the first incision below the mitral ring. The incision should pass between the mitral segments. The left auricle, mitral ring and flaps and the greater portion of the left ventricle are thus exposed and should be inspected. [Illustration: FIG. 38.—Section of left ventricle and auricle, when heart is examined in the body. (After Nauwerck.)]