Abstract
IN a recent communication in Nature1, certain implications of new work on the anatomy of the middle ear region of mammal-like reptiles were discussed. Some further aspects of the evolution of the mammalian middle ear are here briefly noticed. A new synthesis, based on palaeontological evidence, was recently offered2 to 'explain' the nature of the mammalian tympanic cavity. It was suggested that the primitive reptilian tympanic cavity was, in at least some therapsids, supplemented by a recessus mandibularis related to the region of the notched angular bone; and that the mammalian tympanic membrane was formed from the thin external wall of this recess by extension of the old tympanic membrane.
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