Juxtaoral Organ: Ultrastructure and Features Indicating a Mechanoreceptive Function

Abstract

Present knowledge about the history of the discovery, about the development and the morphology of the juxtaoral organ is shortly summarized in a separate contribution (Mayr, this volume). Although regularly present as a paired formation in both cheeks in man, in all other mammals, as well as in certain reptiles (squamates), but not found in other vertebrates (amphibia, aves, pisces), the function of this organ is still unknown. After an extensive study of its comparative anatomy, Salzer and Zenker (1962) introduced the descriptive designation “the juxtaoral organ”, according to the most typical common feature (i.e. the paraoral location) of the homologous organs in mammals and reptiles. Concerning the organ’s functional significance, two lines of suggestions have to be considered: (i) Indications of a secretory function of the parenchyma of the organ, and (ii) morphological features indicating a (mechano-)receptive function of the organ (cf. Zenker, 1982). None of the two suggested functions excludes the other. Therefore, both lines of suggestions would require functional studies for verification. Experimental studies in the rat showed that the organ undergoes a high degree of atrophy after hypophysectomy (Salzer and Zenker, 1968).