ectotympanic ectotympanic the ectotympanic, or tympanicum, is a bony structure found in all mammals, located on the tympanic part of the temporal bone, which holds the tympanic membrane (eardrum) in place. in catarrhine primates (including humans), it takes a tube-shape. its position and attachment to the skull vary between primates, and can be either inside or outside the auditory bulla. it is homologous with the angular bone of non-mammalian tetrapods.