The entotympanic is a bone found in the ear region of many placental mammals. When present it forms the medioventral part of the auditory bulla; it is a neomorphic element derived from the tubal cartilage and the sheath of the tympanohyal. It is found in a wide variety of placental mammals, including Xenarthra, Afroinsectophilia, Hyracoidea, Pholidota, Carnivora, Perissodactyla, Chiroptera, Dermoptera, and Scandentia; it is (apparently secondarily) reduced or absent in Glires, Primates, Eulipotyphla, and Artiodactyla (including Cetacea). [1] It is the only common neomorphic element of the mammalian skull.[2]
The entotympanic contacts the ectotympanic, with which it makes up the auditory bulla.