Nasolacrimal Angle as a Surrogate Measure of Prognathism in Primate and Non‐primate Species

Abstract

The nasolacrimal (NL) apparatus is a structure that has been preserved across mammalian species for its crucial role in the maintenance of ocular function and hygiene. The NL duct, housed within the bony NL canal (NLC), drains tears from the medial aspect of the eye to the posteriosuperior recess in the inferior meatus. Visioni et al. (2006) suggested that the angle of the NLC could be correlated with the degree of prognathism of a species. This study uses gross dissection to measure the NL angle (NLA), formed at the intersection of the distal NLC with the plane of the hard palate, in both non‐primate and primate species. Primate species included: Humans, Rhesus macaque, Cynomolgus and Patas monkeys (n=32) and non‐primate species (domestic pig and bull n=4). Primate specimens were obtained from Dr. Márquez's collection at SUNY Downstate while the bull and pig were obtained from an Amish farm in Philadelphia. All specimens were fixed in 10% formaldehyde prior to gross dissection. Results showed that the highly prognathic species of bulls and pigs have positive acute NLAs averaging 20.17°, whereas the more orthognathic primate species have NLAs approaching 90°. Humans, the most orthognathic primate species, present a negative NLA, reaching an average value of 37°. Our findings indicate that NLAs may be an invaluable resource for determining the degree of prognathism in interspecies comparison studies.