THE ATRIOVENTRICULAR VALVES OF THE MOUSE .1. A SCANNING ELECTRON-MICROSCOPE STUDY

This paper reports a scanning electron microscope study of the morphol ogy of the atrioventricular (AV) valves in the mouse. The leaflet tiss ue of the 2 AV valves consists of a continuous veil that shows no comm issures or clefts. In all instances, the chordae that arise from the p apillary system merge with the free border of the leaflet tissue. No d istinct terminations of chordae were observed on the ventricular face of the valves. The leaflet tissue of the right AV valve can be divided into parietal and septal components on the basis of the insertion int o the ventricular wall and of the papillary system. While the septal c omponent is similar in shape, location and tension apparatus to the se ptal tricuspid leaflet in man, the parietal component appears to corre spond to the anterior and posterior human leaflets. This segment of th e valve is served by 3 papillary muscles that arise from the septal wa ll. The right AV valve is not a tricuspid structure from the morpholog ical standpoint, but appears to function as such because of the partic ular attachment of the papillary muscles. The leaflet tissue of the mi tral valve is served by 2 papillary muscles, anterior and posterior, w hich consist of muscular trabeculae extending from the heart apex to t he base of the valve. These muscles remain associated with the ventric ular wall. The leaflet tissue attaches directly to these papillary mus cles, which give rise to a very small number of slender chordae. There are thus several important differences between the AV valves of the m ouse and man. It is stressed that extrapolation between species cannot safely be made without a thorough knowledge of normal embryology and anatomy.