Diagram of coronal section through bulla of gerbil written by Wolfman and Chole [27]. (a) Normal gerbil (reproduced with modification with permission from Wolfman and Chole [27]). (b) After Eustachian tube cauterization, effusion develops (shaded area) and tympanic membrane retracts (reproduced with modification with permission from Wolfman and Chole [27]). (c) With time, pars flaccida retracts into deep pockets, where keratin accumulates (arrows) (reproduced with modification with permission from Wolfman and Chole [27]).
