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concavity of the membrane (umbo), situated a little below its centre (Fig. 1071); 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 crus of the incus is but faintly visible, and still less so are the promontory and fenestra cochleæ; in the condition of obstruction of the auditory tube (Eustachian), however, in which the membrane is indrawn, these structures, along with the folds of the drum-head, 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 translucent membrane, it is necessary to study the relative position of the structure of the "mesotympanum," 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
Roof of tympanic antrum
FIG. 1074.-SECTION THROUGH PETROUS PORTION OF TEMPORAL BONE OF ADULT.
that the head of the malleus and the body and short crus of the incus are altogether above the tympanic membrane, and that they occupy the tympanic attic or epitympanic recess (Fig. 1074). At the junction of the two upper quadrants of the membrane is the handle of the malleus, which is directed downwards, backwards, and medially. The lateral process of the malleus is directed laterally a little below the deepest part of the roof of the osseous external acoustic canal. Opposite the postero-superior quadrant are the long crus of the incus, which descends behind and almost parallel to the handle of the malleus, and the stapes, which is directed medially and slightly backwards to the fenestra vestibuli. The chorda tympani nerve runs from behind forwards between the lateral surface of the superior part of the long crus of the incus and the medial 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 lateral process of the malleus, is a notch (notch of Rivinus), which is occupied by the flaccid and highest portion of the membrana tympani (Shrapnell membrane). Opposite the postero-inferior quadrant of the drum-head is the promontory caused by the first part of the cochlea, below and behind which is the fenestra cochlea. Opposite the antero-superior quadrant are the processus cochleariformis, the tendon of the tensor tympani, and the passage leading towards the auditory tube.
The labyrinthine wall of the tympanic cavity is related to the internal ear. The tegmental 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
teriorly to form the roof of the osseous portion of the auditory tube, while posteriorly roofs over the tympanic antrum. Laterally the tegmen is limited by the petroquamous suture, which may remain unossified for some years after birth, thus ffording a channel along which pyogenic infection may spread from the middle ear to the meninges and brain. Infection may also spread along the small veins which convey blood rom the tympanum to the superior petrosal and transverse sinuses.
The jugular wall of the tympanum is formed mainly by the bone forming the jugular ossa, which is occupied by the bulb of the internal jugular vein. When the transverse sinus s large and unusually far forward the bulb is likewise large, and the fossa, which is conequently deeper, may arch up into the jugular wall of the tympanic cavity, from which it may be separated merely by a thin and translucent plate of bone which occasionally shows an osseous deficiency. In cases where this condition existed the jugular bulb has been wounded in the operation of paracentesis of the tympanic membrane.
Anteriorly the tympanic cavity leads into the auditory tube, which brings it into communication with the nasal part of the pharynx. In the child the auditory tube is shorter, wider, and more horizontal than in the adult, hence inflammations are more liable to spread along it to the tympanum.
Above the level of the membrana tympani is the epitympanic recess, which communicates posteriorly by means of a triangular opening (aditus ad antrum) with the tympanic antrum; the base of the triangle, directed upwards, is formed by the tegmen tympani ; its apex, directed downwards, is formed by the meeting of the medial and lateral walls. The opening will admit an instrument half a cm. in diameter. The epitympanic recess contains from before backwards the head of the malleus, the body and short crus of the incus, the latter projecting backwards into the aditus. When these structures are covered with inflamed mucous membrane or granulations, drainage from the tympanic antrum into the tympanum proper is interfered with. The boundaries of the aditus, important surgically, are as follows: superiorly, the tegmen tympani; medially, an eminence of compact bone, containing the lateral semicircular canal, inferior and anterior to which is a second smaller prominence, corresponding to that portion of the facial canal which curves immediately above and behind the fenestra vestibuli. The wall of the facial canal is here thin and not infrequently deficient, in which case inflammation may readily spread from the tympanum to the facial nerve. The lateral wall of the aditus is formed by the deepest part of the upper and lateral wall of the osseous external acoustic meatus.
The posterior wall of the tympanum, below the aditus ad antrum, is formed by diploic bone which contains the descending portion of the facial canal.
The tympanic antrum is to be considered, developmentally as well as anatomically, as an extension upwards and posteriorly of the tympanum (Fig. 1073). Its anatomy and relations will be best understood by studying it in the child, in whom it is relatively larger than in the adult. Situated above and posterior to the tympanic cavity proper, its lateral wall is formed by a triangular plate of bone which descends, behind the external acoustic process, from the squamous portion. Posteriorly, this triangular plate is separated from the petro-mastoid element by the squamomastoid suture, which overlies the posterior part of the antrum and transmits small veins to the surface. The suture does not become completely ossified until a year or two after birth, and remains of it may frequently be detected in the adult bone. The anterior and superior portion of the triangular plate turns medially at an angle to form the upper and posterior wall of the rudimentary osseous canal, as well as the floor of the epitympanic recess.
In the adult the lateral wall of the tympanic antrum is formed by a plate of bone, fromtoin. in thickness, which occupies the triangular and somewhat depressed area between the ridge extending, posteriorly and slightly upwards, from the posterior root of the zygoma (supra-mastoid portion of temporal crest), and the superior and posterior quadrant of the osseous external acoustic meatus; upon the latter is the supra-meatal spine, immediately posterior to which, upon the floor of the above triangle, is a crescentic depression, the fossa mastoidea. The lateral wall of the antrum is felt through the skin as a slight depression immediately behind the auricle, and immediately inferior to the ridge formed by the supra-mastoid crest; below the depression is the prominence corresponding to the insertion of the sterno-mastoid muscle. Trautmann has pointed out, however, that the supramastoid crest, which varies considerably in its obliquity, is sometimes situated a little above the level of the roof of the antrum, and that it is safer, therefore, to
take the level of the superior border of the osseous meatus as the guide in order to feri avoid opening the middle fossa of the skull. In children the supra-mastoid creste is not developed, so that if the operator mistake the posterior root of the zygoma for the crest, he will open into the middle fossa of the skull immediately in front the fa of the epitympanic recess. The upper and posterior quadrant of the osseous meatus is therefore the only reliable guide to the antrum in the child.
The medial wall is formed by a thick plate of spongy bone which separates the ter antrum from that portion of the posterior fossa lying between the aqueduct offl the vestibule and the groove for the sigmoid portion of the transverse sinus, and which contains the posterior semicircular canal.
The roof, which slopes downwards and forwards, is formed by the posterior and thinnest part of the tegmen tympani.
The floor is on a lower level than the aditus, and is therefore unfavourably placed for natural drainage.
The mastoid process begins to develop in the second year. As development advances the diplöe surrounding the antrum in the child becomes excavated to
form the mastoid cells, which radiate from the antrum, and either directly or indirectly communicate with it by small openings. In the pneumatic type of mastoid the whole of the process is excavated by these cells, which extend upwards into the squamous portion, forwards to the posterior wall of the osseous meatus (border-cells), and backwards into the occipital bone. Pus retained within the "border-cells" may bulge into, and rupture through, the posterior wall of the osseous meatus. Less frequently the mastoid cells are absent, the bone consisting either of osseous tissue similar to that of the diplöe, or of dense bone (sclerosed type. The mastoid portion of the temporal bone is grooved, upon its medial surface by the sigmoid portion of the transverse sinus. The average distance of the foremost part of the sinus from the supra-meatal spine is 1 cm. The right sinus usually receives the superior sagittal sinus, and when this is the case it is larger and farther forward than the left; in extreme cases it may reach to within 2 or 3 mm. of the meatus. The average minimum distance of the transverse sinus from the outer surface of the mastoid is about 1 cm., but when the sinus is large and far forward the thickness may be reduced to 1 or 2 mm.
The facial nerve, after entering the facial canal at the bottom of the interna acoustic meatus, lies immediately above and behind the fenestra vestibuli, betweer it and the prominence of the lateral semicircular canal; thence it descends almos vertically in the mastoid wall of the tympanum in. posterior and medial to the
nferior half of the deepest part of the posterior wall of the external osseous canal nd emerges through the stylo-mastoid foramen (Fig. 1073).
In the infant, in consequence of the absence of the mastoid process, the exit of he facial nerve from the stylo-mastoid foramen is unprotected and exposed upon he lateral rather than upon the basal surface of he skull, at a point immediately behind the posterior segment of the tympanic horse-shoe. It follows, therefore, that, in infancy, the incision o expose the antrum should not be curved too far downwards and forwards, otherwise the facial nerve may be divided. In the infant the position of the tympanic antrum is relatively higher than in the adult, because in the former the upper wall of the osseous canal inclines towards the vertical plane instead of being horizontal.
The lymph vessels from the auricle and external meatus open into the posterior and anterior auricular lymph glands, the latter receiving also the lymph from the middle ear. The efferent
vessels from those glands open into the superior sub-sternomastoid glands; hence it is that those groups of glands are so frequently found to be diseased secondary to tuberculosis of the middle ear; and care must be taken not to mistake an
abscess in one of the mastoid glands for sub- FIG. 1077.- RIGHT FRONTAL SINUS OF periosteal mastoid suppuration associated with middle-ear disease.
VERY LARGE DIMENSIONS; LEFT SINUS
To open the tympanic antrum the surgeon makes a curved incision a little behind the attachment of the auricle, and chisels or drills away the bone immediately above and behind the postero-superior quadrant of the external osseous meatus. In this operation the middle fossa of the skull is avoided by keeping below the supra-mastoid crest; the transverse sinus, by keeping close to the external acoustic canal and by chiselling obliquely to the surface in opening the mastoid cells; the descending portion of the facial nerve is avoided by not encroaching upon the inferior half of the deepest part of the posterior wall of the osseous canal. In extending the operation from the tympanic antrum through the aditus into the epitympanic recess, the lateral semicircular canal and the curve of the facial nerve, which lie in relation to the medial wall of the aditus, are liable to injury, and must be protected either by a curved probe, or, better, by a Stacke's protector, passed from the antrum through the aditus into the tympanic cavity.
The frontal air sinuses are two cavities situated immediately above the root of the nose between the two tables of the frontal bone. Each sinus at its most dependent part communicates, by means of the naso-frontal duct, either directly with the middle meatus of the nose, or indirectly with that channel through its infundibulum. A bony septum, rarely incomplete, separates the two sinuses; it is usually median in position below, but it may deviate to one or other side above (Figs. 1075 and 1076).
The sinuses vary considerably in their size and shape, independently of the degree of development of the glabella and superciliary arches (Fig. 1077). According to Logan Turner, the dimensions of an average-sized sinus are: height, 11 in., from the lower end of the fronto-maxillary suture vertically upwards; breadth, 1 in., from the median septum horizontally laterally; depth, in., from the anterior wall backwards along the orbital roof. The sinus may exist merely as recesses limited to a small area of bone above the nose, or it may extend upwards on to the forehead for more than two inches; laterally it may be limited by the bony wall of the temporal fossa, while posteriorly it may reach as far back as the optic foramen. The anterior wall is thickest, but the thickness may vary from 1 to 5 mm. The floor is the thinnest wall, hence when pus is retained within the cavity, it tends to point at the superior and medial angle of the orbit. Intra-cranial suppuration may arise in connexion with sinus disease by extension through the roo
or the posterior wall. The muco-periosteal lining, which readily strips from the bone, is thin and pale, and provided with mucus-secreting glands.
In many individuals, by the aid of trans-illumination, the extent of the sinuses and the position of the intervening septum may be mapped out upon the forehead. For this Septum of frontal sinuses Crista galli Left frontal sinus Right frontal sinus
Floor of anterior fossa of skull
Frontal process of maxilla
FIG. 1078.-VERTICAL FRONTAL SECTION THROUGH THE NOSE AND FRONTAL SINUSES.
purpose a small electric lamp is placed against the floor of the sinus, beneath the medial third of the supra-orbital margin.
The skiagraphic appearances of the frontal sinuses are of importance clinically and give more information than trans-illumination. Antero-posterior skiagrams show the vertical extent of the sinus, the degree of asymmetry, and the presence or absence of recesses, with their intervening septum. An orbital expansion is indicated by a welldefined shadow with a sharply-defined upper margin, extending laterally parallel to and immediately above the medial half or more of the supra-orbital margin. A profile skiagram shows not only the height of the sinuses but also their antero-posterior diameter, as well as the degree to which they extend backwards between the roof of the orbit and the floor of the anterior fossa of the skull. While it is exceptional to meet with frontal sinuses before the age of five years, they are almost invariably present by the seventh or eighth year.
In exploring the sinus, the opening in the bone should be made close to the median plane, immediately above the root of the nose. In marked cases of deviation of the septum one sinus may extend so far across the median plane of the forehead as to reduce the other to a mere slit; in such cases the surgeon may fail to open the diseased sinus when the operation is performed through the anterior wall. The sinus frequently contains incomplete partitions, which give rise to the formation of pockets and recesses usual found towards the lateral angle of the sinus; when dealing with chronic suppuration c the sinuses, special attention should be paid to these recesses as well as to the backward extension of the cavity along the orbital roof. The anterior ethmoidal cells are closely related to the thin medial or nasal portion of the floor of the sinus and its duct of erit hence suppuration very frequently co-exists in both cavities. In some cases pus 1 directly from the frontal sinus and infundibulum along the hiatus semilunaris into th maxillary sinus, which opens into the back part of the hiatus. Killian's operation for the cure of chronic suppuration in the sinus consists in the removal of its anterior an inferior walls, the supra-orbital margin being left to prevent the falling in of the eyebro By removing the frontal process of the maxilla good access may at the same time be obtained to the ethmoidal cells and free drainage established between the frontal sincs and the nasal cavity. (Skiagraphs of Frontal Sinuses, see Plates I. and II.)