The sublingua of Lemur catta and Varecia variegata: only a cleaning function?

Abstract

The sublingua is an anatomical structure located under the tongue. This rare organ can be present in some animals as a rudimentary structure, but among prosimian primates, such as lemurs and lorises, it is fully developed. In addition to the sublingua, prosimians have modified lower incisors and canines called "dental comb". The anatomy of sublingua has been studied macro and microanatomically since the early 19th century. Most authors argue that the sublingua is an oral morphological adaptation to develop a toothbrush's role in cleaning the dental comb. However, others assert that the functional role has yet to be established. Comparative studies of macro and microanatomy are scarce or incomplete for primates; thus, the putative function remains unclear. To better understand the functional significance of the sublingua, we studied this structure in Lemur catta and Varecia variegata specimens using histochemical staining techniques and scanning electron microscopy with microanalysis. The new data obtained provide a fuller picture of the role assigned to sublingua so far, which could be more complex. In light of the morphological findings, we should consider additional roles/functions of the sublingua, including but not limited to food processing, grooming or social behavior.