Evolution of the Nasal Structure in the Lower Tetrapods

Abstract

The gross structure of the nasal cavities and the distribution of the various types of epithelium lining them are described briefly; each living order of amphibians and reptiles possesses a characteristic and distinctive pattern. In most groups there are two sensory areas, one lined by olfactory epithelium with nerve libers leading to the main olfactory bulb and the other by vomeronasal epithelium with fibers to the accessory bulb. All amniotes except turtles have the vomeronasal epithelium in a ventromedial outpocketing of the nose, the Jacobson's organ, and have one or more conchae projecting into the nasal cavity from the lateral wall. Although urodeles and turtles possess the simplest nasal structure, it is not possible to show that they are primitive or to define a basic pattern for either amphibians or reptiles; all the living orders are specialized and the nasal anatomy of extinct orders is unknown. Thus it is impossible, at present, to give a convincing picture of the course of nasal evolution in the lower tetrapods.