Sublingua

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.

Tarsiers have a large but highly generalized sublingua, but their closest living relatives, monkeys and apes, lack one.

[12] The point where the plica sublingualis attaches to the rear floor of the mouth marks the location of the submandibular salivary glands.

[14] In tarsiers, the sublingua does not have serrations along its tip and is much simpler and generalized in structure, making it clearly distinguishable from that of the lemuriform primates.

[17] In lemuriform primates, the sublingua is used to remove hair and debris from the highly specialized toothcomb,[6][17] an arrangement of four or six long, forward-facing teeth in the lower jaw used in oral grooming.

[15] Although colugos also have a toothcomb, consisting of serrated edges on the tips of their incisors instead of finely spaced, elongated teeth, they do not have a sublingua.

[17] The sublingua in lemuriform primates and tarsiers may have evolved from the specialized folds of tissue below that tongue, as seen in some marsupials, such as sugar gliders, as well as some embryonic eutherian mammals, such as whales and dogs.

[4][9] The sublingua of treeshrews, close relatives of primates, is less developed than in lemuriforms and tarsiers,[5] but suggests a phylogenetic relationship.

[7][9][14] The structure and appearance of the sublingua, frenal lamella, lingual frenulum, and other sublingual tissue vary greatly between primates, and as a result, their terminology is often confused.