Postnatal development of the middle ear: areal ratios in kittens.

Developmental changes in tympanic membrane to stapedial footplate areal ratios were investigated in kittens from birth through the twentieth postnatal day. Measurements from 45 kittens (85 temporal bones) were obtained from the pars tensa region of the tympanic membrane and the stapedial footplate region bounded by the annular ligament using standard macrophotographic and computer digitization techniques. Tympanic membrane and stapedial footplate areas were approximately 70% and 80%, respectively, of their adult size at birth and relevant areas increased exponentially during early postnatal life. Adultlike dimensions were achieved by the end of the first postnatal week. Tympanic membrane:stapedial footplate areal ratios increased from approximately 25:1 to 30:1 during the first postnatal week, before the developmental period during which adultlike auditory thresholds and response amplitudes are acquired. Thus, the areal ratio influences on impedance-matching characteristics of the middle ear do not appear to significantly affect the postnatal development of auditory function in cats.