Asherson N
J Laryngol Otol. 1978 Jun;92(6):453-65. doi: 10.1017/s0022215100085625.
The fourth auditory ossicle (the Os Orbiculare or Lenticulare, or the Osselet of Sylvius) was described and depicted in all books on anatomy or otology up to the turn of the century. Its presence is no longer observed nowadays, despite the thousands of micro-surgical operations performed on the middle ear and its ossicular chain.