Some features of the mitral valve.

Examination of a series of fresh normal hearts has revealed certain features of the anatomy of the mitral valve that are not mentioned in textbooks of anatomy or in clinical articles. Briefly, the fibrous ring to which the cusps of the mitral valve are attached does not lie in one plane as shown in standard textbooks, and consequently the relationship of the anterior, aortic, or septal cusp of the valve to the left atrium, and to the inflow and outflow channels of the left ventricle, is not that which would be inferred if the ring were in one plane. The fibrous ring, part of the framework of the heart, which separates atrium from ventricle, and to which the cusps of the mitral valve are attached, consists, in its superomedial part, of the borders of the right and left fibrous trigones, and the fibrous wall of the subaortic part of the left ventricular chamber with which they are continuous. The remaining and inferolateral part of the ring is continuous with the trigones (Fig. 3). The ring so formed does not lie in one plane but is hinged about an axis which joins the two commissures of the valve cusps (Figs. 1 and 3). The shape of the anterior cusp can be seen in Fig. 4. Its attached border forms an arc, and its free border is subdivided into three regions: a middle one the centre of which is free from