Meeting Abstract
The nasolacrimal duct (NLD) connects the orbital region to the nasal cavity in most tetrapods. Traditionally, its primary function is considered to drain “excess” fluids of the orbital glands (e.g. the Harderian and lacrimal glands) away from the cornea. The NLD is generally subdivided into two segments: a caudal part within in a bony canal (consisting variably of the lacrimal and maxillary bones) and a rostral membranous portion within the nasal cavity (i.e., passes within the mucosa of the lateral nasal wall, unenclosed by bone). Although the route of this duct has been described in a variety of tetrapod taxa, less is known about its ontogeny. In rodents and lagomorphs, both parts of the NLD develop comparatively early in ontogeny. The rostral opening of the NLD accompanies the narial region as the nose lengthens, obtaining a fairly straight course. In Laysan Albatross and Alligator, the membranous portion forms a very short segment, as the NLD opens into the nasal cavity soon after emerging from the bony canal, roughly in the center of the nasal cavity. In tarsiers, anthropoid primates, and possibly pigs, both parts are formed but the rostral membranous portion falls apart in the perinatal stages, leaving the caudal portion to open into the central nasal cavity slightly rostral to where it emerges from the bony canal. The bony canal thus appears to be conserved in several tetrapods, whereas the rostral, membranous portion, even when present embryologically, may not be retained postnatally. This variable development of the NLD route appears to be associated with alterations of the ultimate function of the nasolacrimal fluids, and the NLD should probably be regarded as far more highly adaptable organ system than traditionally recognized.
