1166 SURFACE AND SURGICAL ANATOMY. 
chronically inflamed it is lable to give rise to secondary periostitis and osseous 
narrowing of the canal. 
The relations of the osseous walls of the canal are of importance to the surgeon. 
The whole of the upper wall and the upper half of the posterior wall, developed 
from the squamous portion of the temporal bone, consist of two layers of 
compact bone, an upper and a lower, which are continuous, the former with the 
inner table, the latter with the outer table of the skull. The upper plate passes 
inwards to the petro-squamous suture, where it becomes continuous with the outer 
edge of the tegmen tympani, which roofs over the tympanic attic and the mastoid 
antruin; the lower plate bends downwards and inwards at its deepest part to form 
the lower and outer wall of the tympanic attic and the anterior part of the outer 
wall of the antrum (Trautmann). It follows, therefore, that when the mastoid 
antrum is abnormally small, due to sclerosis of the bone, or when it is encroached 
upon by a far-forward lateral sinus, it, along with the tympanic attic, can 
be opened by perforating the junction of the upper and posterior walls of the 
osseous canal, the instrument being directed inwards and slightly upwards. Upon 
the upper and posterior segment of the external auditory process is the supra- 
meatal spine; this small but important process, developed from the squamous 
Roof of mastoid antrum Posterior branch of middle meningeal artery 
| Anterior branch of middle meningeal artery 
| 
| | Shad 
Posterior part of middle fossa of skull 
Portion of cerebellar fossa 
forming posterior wall of 
mastoid antrum 
Interior of lateral sinus- \ 
rds 
Anterior limit of lateral sinus 
Mastoid antrum 
BAZ 
\ \ ~ Spheno-temporal sinus 
; \ NY Trunk of middle meningeal artery 
Incus ; \ Tegmen tympani 
Membrana tympani Chorda tympani nerve 
Head of malleus 
Fic. 794.—ViIEW OF THE OUTER WALL OF THE MIDDLE Ear. 
Section through the left temporal bone of a child, to show the relations of the middle ear and mastoid antrum 
to the middle and posterior fosse of the skull. 
portion, can usually be distinctly made out in the living subject by pressing 
upwards and backwards with the forefinger placed in the external auditory meatus. 
The lower half of the posterior wall of the osseous canal (posterior part of the 
tympanic plate) is fused with the anterior part of the mastoid process, and closes 
the lower and anterior set of mastoid cells (border cells). 
Anteriorly and inferiorly the osseous canal is related respectively to the 
temporo-maxillary articulation and the parotid gland; hence it follows that blows 
upon the chin may fracture the tympanic plate as well as the base of the skull, 
that pain on mastication is usually complained of in acute inflammatory affections 
of the meatus and middle ear, and that in young children, in whom the tympanic 
plate is incompletely ossified, suppurative inflammation is liable to extend from the 
ear to the parotid region. 
Clinically, to obtain a view of the membrana tympani a speculum and a reflecting 
mirror are employed; the auricle is pulled upwards, backwards, and outwards, in order 
to straighten the cartilaginous part of the canal. The healthy membrane is pearly gray, 
semi-opaque, slightly concave outwards, and obliquely placed, being inclined outwards, 
especially above and behind. 
The handle and short process of the malleus, both embedded in the membrana tympani, 
are the only objects distinctly seen when the healthy ear is examined with the speculum. 
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