Sublingua
The sublingua ("under-tongue") is a muscular secondary tongue found below the primary tongue in tarsiers and living strepsirrhine primates, which includes lemurs and lorisoids (collectively called "lemuriforms"). Although it is most fully developed in these primates, similar structures can be found in some other mammals, such as marsupials, treeshrews, and colugos. This "second tongue" lacks taste buds, and in lemuriforms, it is thought to be used to remove hair and other debris from the toothcomb, a specialized dental structure used to comb the fur during oral grooming. A rigid structure called the plica mediana or lytta runs from the front to the back, down the center of the sublingua to give it support. The plica mediana is usually made of cartilage and attaches the sublingua to the underside of the tongue. In lemuriforms, the sublingua mostly consists of two plicae fimbriatae (singular: plica fimbriata), which run along the sides of the plica mediana and end in comb-like serrated edges that are hardened with keratin. The plicae fimbriatae move freely over a limited range. The plica sublingualis, which is found in all primates, but is particularly small in lemuriforms, attaches the tongue and sublingua to the floor of the mouth. Tarsiers have a large but highly generalized sublingua, but their closest living relatives, monkeys and apes, lack one. The sublingua is thought to have evolved from specialized folds of tissue below the tongue, which can be seen in some marsupials and other mammals. Simians do not have a sublingua, but the fimbria linguae found on the underside of ape tongues may be a vestigial version of the sublingua. Because of widely variable appearance of sublingual tissue in primates, the term "sublingua" is often confused with the frenal lamella, lingual frenulum, and other sublingual tissues. Anatomical structure The sublingua, or "under-tongue", is a secondary tongue located below the primary tongue in tarsiers, lemuriform primates, and some other mammals. This structure does not have taste buds or salivary glands. In lemuriforms, the sublingua is relatively large and its front edge is usually lined with keratinized serrations (sometimes called "denticles"). Down the middle of the sublingua is a thick strengthening rod called the plica mediana or lytta, which connects the sublingua to the underside of the tongue, and is part of the lingual septum (septum of the tongue). The thickness and size of the plica mediana can vary between species, and except in treeshrews, it is cartilaginous and provides support for the sublingua. Only the serrated and often keratinized tip of the sublingua is free to move small distances along the underside of the tongue, while the majority of its length adheres to the underside of the tongue. These free-moving folds or filaments are called the plica fimbriata and attach to the base of the sublingua and are supported at the midline by the plica mediana. The plica fimbriata is highly developed and specialized in lemurs, and makes up the majority of the sublingua. The fold that connects the back of the sublingua and