The Structure, Development, and Operation of the Hinge Ligament of Ostrea edulis

Abstract

ABSTRACT The ligamental structure of Ostrea edulis is briefly described. The ligament is situated between the valves of the shell immediately below the urtibo and may be divided into two main layers, the outer and the inner, the principal features of which appear to correspond with those of other bivalves. The outer layer is divided into anterior and posterior halves by the inner layer, which occupies a central position. The axis (hinge or pivotal axis) about which the valves open is situated in the adult oyster along a line drawn through the outer layer and the upper part of the inner layer. When the valves are closed the ligament above this axis is subjected to a tensile strain and that portion below to compression, the forces so produced causing the opening of the valves. An attempt has been made to measure this force in relation to the surface area of the valves and it is found to be approximately 4·5 gm. mm./mm.2 This figure is comparable to those obtained when certain other species of bivalves are used. The ligament is shown to develop from the simple outer layer of the early larval stages, first by the addition of an inner layer and then by growth of this structure chiefly in a ventral direction. The initial dorsal region of the ligament soon degenerates and at the same time the pivotal axis moves ventrally between the valves, thus increasing in length. This method of growth is compared with that of an elongate external ligament and the mechanical implications are suggested.