Tectorial Reticulum of the Labyrinthine Endings of Vertebrates

Abstract

A special layer of tectorial tissue, usually in the form of a fibrous network, that was first discovered in the macular and crista endings of the frog's labyrinth, has now been identified in these endings in representatives of all the other vertebrates, and therefore is considered to be a universal feature of the labyrinthine sense organs. This tectorial layer is located between the otolithic and cellular layers and is clearly distinct from both of these. In properly fixed and prepared material this structure is easily seen in the macular endings, where the difference in tissue composition between it and the otolithic ground substance can be demonstrated by selective staining. The primary function of this tectorial reticulum is the stimulation of the hair cells. It makes all the connections to the ciliary tufts of these cells, and is instrumental in conveying to them the differential motions produced by the overlying otolithic or cupular masses. Still further functions of this tectorial layer are suggested. There is reason to believe that it assists the sensitivity of the vestibular organs by converting pressure changes into shearing forces that are well distributed over the sensory surface, and involve a broad area of the hair cells in concerted action. It seems clear also that this structure has a protective function in transmitting the forces from the overlying masses of the ending indirectly through the flexible strands of its network rather than by direct connections that might be disruptive when stimulation is excessive. This layer may also provide elastic restorative forces that bring the ending back to an equilibrium condition after each stimulation.