I wish to describe briefly some of the points of difference between the os temporale of the infant and that of the adult.
In the os temporale of the nine-months fetus1 the ossification of the three centers is well advanced, so that they are all attached to each other, but neither firmly nor throughout the whole of their adjoining edges. The squama temporalis is thin and light. In its posterior portion is seen the series of perforations which mark the outer wall of the antrum tympanicum (which is often incorrectly called the antrum mastoideum but which distinctly is not a part of the processus mastoideus). The processus zygomaticus is light. The fossa mandibularis is merely a shallow depression below the posterior extremity of the processus zygomaticus. The middle and posterior roots of the processus zygomaticus are distinct, but the anterior root has not yet appeared.
The annulus tympanicus is a