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ventricle may be opened up by making a somewhat larger trephine opening parating the posterior extremities of the tonsillar lobes of the cerebellum. expose a hemisphere of the cerebellum, trephine over the centre of a line drawn ne tip of the mastoid process to the external occipital protuberance. expose both hemispheres of the cerebellum a flap is turned downwards by g a curved incision between the bases of the mastoid processes, the centre of ision reaching upwards to a little above the inion. The occipital arteries are

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Fig. 1069.-CRANIO-CEREBRAL TOPOGRAPHY. uiding lines (Chiene's), deep black ; sutures, fine black; meningeal arteries, red ; sulci, blue. lla.

C. Mid-point of AB. nal occipital protuberance (inion).

CD is drawn parallel to AM. joint between G and 0.

z. Post-auricular point. oint between M and 0.

VW. Guide to anterior limit of transverse sinus. point between T and 0.

Y. Tympanic antrum. natic process of frontal.

X?. Site at which subarachnoid space may be opened. of zygoma (pre-auricular point).

X? Site for draining lateral ventricle (Kocher). point of EP.

X. Site for draining lateral ventricle (Keen). point of Ps.

but the anterior extremities of the incision should, if possible, be kept the mastoid emissary veins. As the flap contains the suboccipital muscles ne itself may be removed. If more room is required, the opening in the ay reach above the level of the transverse sinuses without wounding them y can be displaced along with the dura. The occipital sinus is divided n two ligatures. After dividing the dura a hemisphere of the cerebellum

displaced towards the median plane to enable the finger to be passed between it and the posterior surface of the petrous portion of the temporal bone as far as the acoustic nerve, which occupies the angle between the cerebellum and the pons.

Meningeal Arteries. When the calvaria is removed the meningeal arteries are found to adhere firmly to the dura. Of these vessels the middle meningeal artery is the only one of surgical importance. It is frequently lacerated in fractures of the skull; the blood is generally extravasated between the dura and the bone, and the bleeding point lies beneath the clot. After entering the cranial cavity through the foramen spinosum, the main trunk, which is usually about 1} in. in length, runs laterally and slightly forwards to bifurcate into anterior and posterior divisions at a point a finger's-breadth above the middle of the zygomatic arch, viz., at or close behind the point N, Fig. 1069. When the main trunk is short the bifurcation takes place opposite the middle of the zygomatic arch.

The anterior and larger division passes upwards, with a slight forward convexity, a little behind the spheno-squamosal suture and across the pterion to the sphenoid angle of the parietal bone. From that point the vessel is continued upwards and slightly backwards, behind the coronal suture; it gives off branches which ascend over the motor area. The position and general direction of the anterior branch may be said to correspond to the line MN; it follows, therefore, that the artery will be encountered in trephining over the lower and anterior part of the Rolandic area, especially over the motor centres for the tongue and face.

The posterior division passes almost horizontally backwards, towards the mastoid angle of the parietal bone.

To expose the trunk of the vessel and its bifurcation, the trephine is applied immediately above the middle of the zygomatic arch. To expose the anterior division the pin of the trephine may be applied at the point A, which strikes the artery as it crosses the pterion and grooves the sphenoidal angle of the parietal bone. The inferior segment of the disc of bone removed is much thicker than the superior, as it involves the prominent ridge which passes from the tip of the great wing of the sphenoid on to the sphenoidal angle of the parietal bone. At the sphenoidal angle of the parietal bone, the artery frequently runs in a canal for å distance of half an inch. It follows, therefore, that a considerable thickness of bone has to be sawn through at the inferior segment of the circle before the dise can be removed, and during the removal bleeding may occur from the artery as it lies in the canal.

Vogt localises the anterior division at a point a thumb's-breadth behind the tubercle on the posterior border of the zygomatic bone and two fingers’-breadth above the zygoma.

Krönlein trephines at a point 14 in. behind the zygomatic process of the frontal, on a line drawn from the supra-orbital margin backwards parallel to Reid's base-line. If the centre of the trephine be placed at the mid-point of the lower third of the line MA, the anterior division will be reached above the canal and the ridge at the sphenoidal angle of the parietal; if the bleeding-point is lower down, the trephine opening may be enlarged downwards along the line AN.

The course of the posterior division may be indicated upon the surface by drawing a line backwards from the point N parallel to PR, that is to say, a finger'sbreadth above the zygoma and the supra-mastoid crest.

When the frontal branch of the anterior division is injured, the clot is in the fronto-temporal region, and involves more especially the motor area for the face, and, on the left side, Broca's convolution ; when the anterior division is wounded, the clot, which is larger, involves the parietotemporal region, and the motor symptoms are due to pressure upon the centres for the arm and face; in injuries to the posterior division the clot overlies the parieto-occipital region, and the localising symptoms are sensory (Krönlein). In more extensive meningeal hæmorrhage the clo; may cover the greater part of the hemisphere.

The superior sagittal sinus, which enlarges as it extends backwards, occupies the median plane of the vertex from the glabella to the internal occipital protuberance where it opens into the confluens sinuum, and becomes continuous usually with the right transverse sinus. Opening into the sinus, especially in the posterior part of the parietal region, are the para-sinoidal sinuses, into which arachnoideal granulations project. In opening the skull over the posterior part of the vertex, the edge of the trephine should be kept at least three-quarters of an inch from the median plane

ne transverse sinus may be mapped out on the surface by drawing a line, ly convex upwards, through a point a little above the inion to the asterion 1. behind and 1 in. above the centre of the external acoustic meatus) at, or le in front of, the point R, Fig. 1069, and thence in a downward and forward ion to a point } in. inferior and posterior to the centre of the external acoustic is, where it finally curves medially and forwards to open into the jugular which occupies the jugular foramen. According to Moorhead the highest f the sinus lies a finger's-breadth above the middle of a line extending from ion to the middle of the external acoustic meatus. The anterior border of scending or mastoid portion of the sinus may be mapped out by drawing a W from a point a finger's-breadth behind the post-auricular point of the -ral crest to the anterior border of the tip of the mastoid process. In Is of the sinus the hæmorrhage is very free, owing to the inability of its to collapse, but the bleeding is easily controlled by plugging. the cerebral arteries, the middle supplies almost the whole of the motor area, e of its lenticulo-striate branches, which enters the brain at the anterior per1 substance, is called “the artery of cerebral hæmorrhagefrom the frequency rupture in apoplexy. The extravasated blood involves the motor part of the al capsule. The postero-medial central branches of the posterior cerebral , which enter the brain at the posterior perforated substance, supply the nus and walls of the third ventricle; hæmorrhage from one of these branches is rupture into the ventricle. The postero-lateral central branches of the poscerebral artery supply the thalamus, and when one of these vessels ruptures morrhage is apt to invade the posterior or sensory part of the internal capsule. milunar Ganglion.—The topography of the semilunar ganglion is of imce in relation to its surgical extirpation for trigeminal neuralgia. anglion is situated in the dura at the apex of the petrous portion of the ral bone, at the medial part of the middle fossa of the base of the skull. irgeon reaches it by an extra-dural route through an opening in the anterior wer part of the temporal fossa immediately above the zygomatic arch. The s removed down to or, even better, beyond the level of the infra-temporal which forms the boundary line between the lateral and basal portions of the m. By temporarily resecting and depressing the zygomatic arch a portion

floor of the middle fossa, medial to the infra-temporal crest, can be ed. The dura is separated from the fossa so as to admit of the ligature of iddle meningeal artery immediately after its entrance into the cranium h the foramen spinosum. By separating the dura still further in a medial rward direction, the mandibular division of the trigeminal nerve is exposed nters the foramen ovale, and, after it, the smaller maxillary division, as it in a forward and slightly downward direction to enter the foramen rotundum. oose the ganglion itself and the trunk of the nerve the dura is then carefully ted in a backward and medial direction ; in doing this care must be taken

wound the cavernous sinus and the trochlear and abducent nerves which its lateral wall. The oculo-motor nerve and the carotid artery are less to be injured. The ganglion has a grayish-red colour and a felted surface, che portio inajor or trunk of the trigeminal nerve is almost white, and striated adinally. After dividing the mandibular and maxillary divisions of the nerve o their foramina of exit, the ganglion is seized with forceps and removed by ng it away from its trunk and the first division. r.--The skin covering the lateral surface of the auricle is tightly bound to the perichondrium, hence inflammations of it are attended with little ng but much pain. The posterior auricular artery, which ascends along the at the posterior attachment of the auricle, is immediately anterior to the n for opening the tympanic antrum. e external acoustic canal, the general direction of which is medially, for

and downwards, possesses various curves of practical importance. The t part of the upward convexity, which is also the narrowest part of the canal, ated at the centre of its osseous portion ; beyond this the floor sinks to form ss in which foreign bodies are liable to be imprisoned. Of the two horizontal curves the lateral is convex forwards, the medial concave forwards. The skin of the osseous portion of the canal is thin and fused with the periosteum, hence when chronically inflamed it is liable 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

Roof of tympanic antrum
Posterior part of middle fossa of skull

Posterior branch of middle meningeal artery

Anterior branch of middle meningeal artery

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Portion of cerebellar fossa forming posterior wall of

tympanic antrum Interior of transverse sinus

Anterior limit of transverse sinus

Spheno-temporal sinus
Tympanic antrum

Trunk of middle meningeal artery

Tegmen tympani
Membrana tympani

Chorda tympani nerve

Head of malleus Fig. 1070.–VIEW OF THE LATERAL WALL OF THE MIDDLE EAR. Section through the left temporal bone of a child, to show the relations of the tympanum and tympanic antram

to the middle and posterior fossæ of the skull.

compact bone, a superior and an inferior, which are continuous, the former with the inner table, the latter with the outer table of the skull. The superior plate passes medially to the petro-squamosal suture, where it becomes continuous with the lateral edge of the tegmen tympani, which roofs over the epitympanic recess and the tympanic antrum; the lower plate bends downwards and medially at its deepest part to form the lower and lateral wall of the recess and the anterior part of the lateral wall of the antrum (Trautmann). It follows, therefore, that when the tympanic antrum is abnormally small, due to sclerosis of the bone, or when it is encroached upon by a far-forward transverse sinus, it, along with the epitympanic recess, can be opened by perforating the junction of the upper and posterior walls of the osseous canal, the instrument being directed medially and slightly upwards. Upon the upper and posterior segment of the external acoustic margin is the suprameatal spine ; this small but important process, developed from the squamous portion,

can usually be distinctly Posterior tympano- made out in the living submalleolar fold Lateral process of

ject by pressing upwards Membrana flaccida

and backwards with the Anterior tympano

forefinger placed in the malleolar fold

Postero-superior external acoustic meatus. quadrant

The lower half of the Handle of malleus Antero-superior

Postero-inferior

posterior wall of the osseous quadrant

quadrant

canal (posterior part of the

Cone of light Antero-inferior

tympanic plate) is fused quadrant

with the anterior part of the mastoid process, and

closes the lower and anterior Fig. 1071. – LEFT TYMPANIC MEMBRANE (as viewed from the external acoustic meatus). 3. (From Howden.)

set of mastoid cells border

cells) Anteriorly and inferiorly the osseous canal is related respectively to the mandibular articulation and the parotid gland; hence it follows that blows upon the

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icture the tympanic plate as well as the base of the skull, that pain on
is usually complained of in acute inflammatory affections of the meatus
ear, and that in young children, in whom the tympanic plate is incom-
fied, suppurative inflammation is liable to extend from the ear to the
lon.
y, to obtain a view of the membrana tympani a speculum and a reflecting
mployed; the auricle is pulled upwards, backwards, and laterally in order to

Middle fossa of skull usor tym pani muscle

Processus cochlearifornis

Eminence of lateral
semicircular canal

Tympanic antrnm

Tranverse sinus

Posterior fossa of skull

Auditory tube

Rudimentary mastoid process
Facial nerve
Pyramid

Section of jugular fossa
Retro-pharyngeal lymph gland

Stapes
Internal carotid artery

Internal jugular vein Promontory
Fig. 1072.-View OF THE LABYRINTHINE WALL OF THE MIDDLE EAR.
hrough the left temporal bone of a child, to show the relations of the tympanum and tympanic antrum

to the middle and posterior fossæ of the skull.

ten the cartilaginous part of the canal. The healthy membrane is pearly gray, semi-
e, slightly concave, and obliquely placed, being inclined laterally, especially above
hind.
he handle and lateral process of the malleus, both embedded in the membrana tympani,
e only objects distinctly seen when the healthy ear is examined with the speculum.
Groove for posterior branch of middle meningeal artery
Aditus ad antrum

Middle cranial fossa

Tegmen tympani

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Epitympanic recess

-- Chorda tym pani nerve
Tensor tympani muscle

Tympanic antrum

Handle of malleus
-Carotid canal
-Tympanie membrane

--Styloid process
Mastoid process

Stylo-mastoid foramen
Fig. 1073. — SECTION THROUGH LEFT TEMPORAL BONE, SHOWING TYMPANIC WALL OF TYMPANIC CAVITY, ETC.
The lateral process of the malleus projects laterally, and presents itself, therefore, as a
distinct knob-like projection at the superior part of the membrane ; passing forwards and
backwards from this process are the anterior and posterior malleolar folds of the membrana ;
they form the lower limit of the pars flaccida of the 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 backwards to the point of maximur

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