Description of an optic spine on the sphenoid bone of camels and dromedaries

Abstract

Objective To describe the presence of an intraorbital cylindrical osseous structure (a spine) in two animal species: camel (Camelus bactrianus) and dromedary (Camelus dromedaries). A homologous osseous structure was previously observed in the large fruit-eating bat (Artibeus lituratus). Procedures The bony anatomy of the orbital cavity was studied and quantified on macerated skulls of 3 camels and 2 dromedaries. Additionally, one macerated skull of a large fruit-eating bat (Artibeus lituratus) was used for comparative purposes. Results The anatomic description of these unique intraorbital spine was made while studying the bony orbit of macerated skulls, and was considered homologous to that of the bat based on the same anatomic position (at the bone bridge that separates the optic canal and the sphenorbital fissure) and similarities in shape. We suggest the name optic spine of the sphenoid bone. Discussion The novel observation of an optic spine on the sphenoid bone in camels and dromedaries (Artiodactyla), when combined with the previous finding of a similar anatomic structure in a bat (Chiroptera) suborder Microchiroptera, may provide further support to the close proximity of these two apparently very distinct animal orders in the phylogenetic tree, and may contribute to the understanding of bat evolution and provide new directions for future research. The function of this osseous spine remains to be investigated, although we hypothesize that the optic spine of the camelids may serve as an attachment site for extraocular muscles.