Licence: In copyright
Credit: Manual of human osteology / by A. Francis Dixon. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
313/338 page 297
![easily overlooked. After birth, as the edge of the annulus tympanicus grows outwards to form the meatus acusticus externus, the fossa mandibularis becomes deeper and better marked. The isolated os temporale should next be carefully examined. By detaching the squamo-zygomatic part from the petro-mastoid portion, a view of the antrum tympanicim, or mastoid antrum, can be obtained. 'I'his is a small air-space which leads back- wards from the upper part of the cavum tympani. In the adult it lies deep from the surface of the bone, and communicates with the air-cells which are contained in the processus mastoi- deus. In the child’s skull the antrum lies near the surface of Squamo-zvgomatic the head, and its outer wall will be seen to be formed in part by a thin post auditory process of the squamo-zygomatic part of the os temporale. In the adult, owing to the growth of bone which takes place in this region, the antrum lies about half an inch from the surface of the os temporale formed by the floor of the supra-meatal triangle (see page 185). 'I'he foramen stylo-mastoideum will be found on the petro- mastoid portion of the os temporale, immediately below and behind the apex of the post auditory process of the squamo- zygomatic part of the bone. On the posterior surface of the pars petrosa of the os temporale, the fossa sub-arcuata is very conspicuous, and the ])rominence due to the semicircular canal, which arches over it, i.s very marked. After birth the fossa gradually becomes less and less distinct, and in the adult it is merely represented by a slight scar-like mark. The squamo-zygomatic portion of the os temporale is ossified in the membranous wall of the early cranium ; the petro-mastoid](https://iiif.wellcomecollection.org/image/b21932384_0313.jp2/full/800%2C/0/default.jpg)
