The marginal fiber mass in the utricle of the pigeon

Abstract

The marginal fiber mass (MFM) that Werner 26 described in the utricle ofAves was observed and analyzed in the pigeon using light, scanning electron, and transmission electron microscopic techniques. Morphologically, the MFM is a gelatinous, fibrous mass which has the shape of an oblique cone. The basal end terminates as a foot-like structure on the macula utriculi while the apical end attaches the statoconial membrane securely to the wall of the utricle. Specific tests for elastin, collagen and a ‘connective tissue type’ of reticulum indicated that none of these components were present in the MFM. The MFM did, however, stain positively with PAS, Alcian blue and a PAS-Alcian blue combination. The extent and location of the staining suggest that the main bulk of the MFM is comprised primarily of neutral mucopolysaccharides with traces of acid mucopolysaccharides on its surfaces. Based on these facts, and on other morphological observations, it is suggested that the MFM is a marginal extension of the cupular zone of the statoconial membrane which has folded back over on itself and, in the process, has sandwiched the statoconial (otolithic 7) zone between itself and the cupular zone. As a well-developed structure of the avian utricle, the MFM must be considered as a functional component in any biodynamical model of statoconial membrane displacement.