——— 
a 
THE CRANIUM. 1167 
The short process of the malleus projects outwards, and presents itself, therefore, as a 
conspicuous object at the upper part of the membrane ; passing forwards and backwards 
from this process are the anterior and posterior folds of the membrana tympani; they 
form the lower limit of Shrapnell’s membrane, and correspond to the line of the chorda 
tympani nerve. The handle of the malleus, situated at the junction of the two upper 
quadrants, is seen passing downwards and slightly backwards to the point of maximum 
concavity of the membrane (umbo), situated a little below its centre ; passing downwards 
and forwards from the umbo is the triangular cone of reflected light, to which too much 
importance must not be attached, since its appearances vary considerably in healthy 
ears. Normally, the long process of the incus is but faintly visible, and still less so 
are the promontory and foramen rotundum ; in the condition of Eustachian obstruction, 
however, in which the membrane is indrawn, these structures, alone with the folds of 
the drum, become more distinct. 
In performing the operation of paracentesis of the tympanic membrane the postero- 
inferior quadrant is the site chosen for making the puncture, as, in addition to providing 
good drainage, it is farthest removed from important structures, especially the chorda 
tympani nerve. 
In order to understand the clinical importance of the parts seen through the trans- 
lucent membrane, it is necessary to study the relative position of the structure of the 
; Processus cochleariformis ) 
Middle fossa of skull | Eminence of external ] | 
semicircular canal 
| Mastoid antrum 
Tensor tympani muscle x 
~Lateral sinus 
< : 
Posterior fossa of skul? 
» ~ 
xX "Rudimentary mastoid process 
Facial nerve 
Pyramid 
Section of jugular fossa 
Stapes 
Eustachian tube~ \ 
Retro-pharyngeal lymphatic gland 
Internal carotid artery | 
Internal jugular vein Promontory 
Fic. 795.—VIEW OF THE INNER 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 fossz of the skull. 
“meso-tympanum,” that is to say, that part of the tympanum which lies opposite the 
tympanic membrane. If the tympanic plate and the tympanic membrane be carefully 
removed so as to leave the ossicles and chorda tympani nerve in position, it will be seen 
that the head of the malleus and the body and short process of the incus are altogether 
above the tympanic membrane, and that they occupy the tympanic attic or epitympanic 
space. At the junction of the two upper quadrants of the membrane is the handle 
of the malleus, which is directed downwards, backwards, and inwards. The short process 
of the malleus is directed outwards a little below the deepest part of the roof of the 
osseous external auditory canal. Opposite the postero-superior quadrant are the long 
process of the incus, which descends behind and almost parallel to the handle of the 
malleus, and the stapes, which is directed inwards and slightly backwards to the foramen 
ovale. The chorda tympani nerve runs from behind forwards between the outer surface 
of the upper part of the long process of the incus and the inner surface of the neck of 
the malleus. At the deepest part of the roof of the osseous canal above the chorda 
tympani nerve and the short process of the malleus is a notch (notch of Rivind), which 
is occupied by the flaccid and highest portion of the membrana tympani (Shrapnell’s 
membrane). Opposite the postero-inferior quadrant of the drum-head is the promontory 
of the cochlea, below and behind which is the foramen rotundum. Opposite the antero- 
superior quadrant are the processus cochleariformis, the tendon of the tensor tympani, and 
the passage leading towards the Eustachian tube. 
The inner wall of the tympanic cavity is related to the internal ear. The upper wall 
is Separated from the middle fossa of the skull and the under surface of the temporal 
lobe of the brain by the tegmen tympani—a thin plate of bone, which is continued 
