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behind the zygomatic process of the frontal bone above; inferiorly it passes through the alveolar process of the maxilla in the interval between the first and second molar
teeth. The cranial, orbital, nasal, and maxillary cavities are all exposed, together with the roof of the mouth.
The anterior cranial fossa is deepest in its centre, where its floor is formed by the cribriform plate of the ethmoid ; this corresponds to the level of the zygomatico-frontal suture laterally. On either side the floor of the fossa bulges upwards, owing to the arching of the roof of the
orbit. Of the orbital walls, the 10 lateral is the thickest and stoutest;
the superior, medial, and inferior 11 walls, which separate the orbit
from the cranial cavity, the eth
moidal cells, and the maxillary 13 sinus, respectively, are all thin.
The cavity of the maxillary sinus lying to the lateral side of the nasal cavity is well seen. Its roof, which separates it from the orbital cavity, is thin and traversed by the infraorbital canal. Its medial wall, with which the inferior concha articulates, is very slender, and forms the lateral walls of both the middle and inferior meatuses of the nose.
Its lateral wall is 17
stouter where it arches up to bracket the temporal process of the zygomatic bone. Its floor, which rests upon the superior surface of the alveolar border of the maxilla, sinks below the level
of the hard palate. The fangs Fig. 176.–FRONTAL SECTION PASSING INFERIORLY THROUGH
of the teeth sometimes project THE INTERVAL BETWEEN THE FIRST and Second Molar Teeth. into the floor of the cavity. The frontal and maxillary bones, where cut, are coloured blue ;
The nasal cavities are narrow the ethmoid, inferior conchæ, and zygomatic red; the vomer yellow. above, where they lie between 1. Groove for sagittal sinus. 12. Zygomatico-frontal suture. the orbital cavities, from which 2. Crest for attachment of falx 13. Infra-orbital groove. they are separated by the cells cerebri. 14. Maxillary sinus.
within the labyrinth of the 3. Crista galli of ethmoid. 15. Canal for the anterior alveolar 4. Cribriform plate of ethmoid.
The roof which cornerve and vessels exposed.
ethmoid. 5. Perpendicular part of eth- 16. Inferior concha.
responds to the cribriform plate moid, assisting in the forma- 17. Inferior meatus of nose. is narrow, and lies between the
tion of the nasal septum. 18. Alveolar process of maxilla. 6. Labyrinth of ethmoid con- 19. Groove for posterior palatine septum medially and the labysisting of the ethmoidal cells.
rinth on either side.
nerve and greater palatine 7. Lamina papyracea of ethmoid. vessels.
At the level of the orbital floor 8. Middle meatus of nose. 20. Palatine process of maxilla. the nasal cavities expand later9. Middle concha.
21. Maxillary crest forming part ally, the middle meatus running 10. Opening from middle meatus of nasal septum.
into maxillary sinus. 22. Voiner forming part of nasal longitudinally in the angle formed 11. Orbital surface of maxilla.
by the labyrinth of the ethmoid
with the body of the maxilla, overhung by the middle concha. This channel is seen to have the ethmoidal cells superior to it, the orbital cavity above and to the lateral side, the maxillary sinus laterally, whilst its floor is formed by the superior surface of the inferior concha.
The inferior meatus, much more roomy, runs along under cover of the inferior
concha. Laterally it is related to the maxillary sinus, whilst its floor is formed by the concave superior surface of the hard palate.
The hard palate is arched below, whilst its superior surface is concave upwards on either side of the median crest which supports the nasal septum. The sides of the arch below correspond to the medial surfaces of the alveolar processes and fall in line with the lateral walls of the nasal cavities superiorly. The summit of the arch lies a quarter of an inch above the level of the floor of the maxillary sinus.
The next section (Fig. 177) passes through the pterygo - palatine and temporal fosse inferiorly, and cuts the cranial vault about half an inch in front of the bregma. The floor of the anterior cranial fossa is seen to be formed by the upper surface of the body and small wings of the sphenoid, and is almost horizontal. At the median plane the sphenoidal sinuses are exposed, separated by a thin bony partition, on either side of which the openings by which they communicate with the nasal cavities are seen. The section passes in front of the optic foramen, the groove of which may be seen on the inferior surface of the small wing of the sphenoid close to the body, and lays open
-10 the superior orbital fissure which here leads forwards into the orbit, and which, inferiorly and laterally, is continuous with the cleft between the maxilla and the lower edge of the great wing of the sphenoid—the inferior orbital fissure. This also leads into the orbit.
The nasal cavities, now much diminished in height, are roofed in above by
20 the inferior surface of the body of the sphenoid and the alæ of the vomer, whilst the lateral walls are seen to be Fig. 177.-FRONTAL SECTION PASSING THROUGH THE formed by the thin perpendicular parts
PTERYGO-PALATINE Fossa. of the palate bones, lateral to which
1. Depression for arach- 10. Zygomatic process of the rounded posterior surface of the
maxilla, maxilla is directed backwards, here 2. Groove for sagittal sinus. 11. Surface of maxilla which forming the anterior wall of the 3. Crista galli of ethmoid.
forms the anterior wall pterygo - palatine fossa
4. Opening of sphenoidal of the pterygo-palatine
sinus into superior fossa. which lies between the anterior part of
meatus of nose through 12. Spheno-palatine foramen. the pterygoid process behind and the
spheno - ethmoidal re- 13. Opening of pterygo-palamaxilla anteriorly. As will be seen, cess.
tine canal. the medial wall of this space is formed
5. Superior orbital fissure. 14. Perpendicular part of
6. Part of middle fossa by the perpendicular part of the palate,
formed by cerebral 15. Pterygoid fossa. which is, however, deficient above im- surface of great wing 16. Superior meatus of nose. mediately below the inferior surface of of sphenoid.
17. Middle meatus of nose. the body of the sphenoid. In the in- 7. Zygomatic crest of great 18. Inferior meatus of nose. terval between the orbital process, which
wing of sphenoid. 19. Inferior concha.
8. Inferior orbital fissure. 20. Middle concha. lies in front of the section, and the 9. Zygomatic process of 21. Maxillary crest and vomer sphenoidal process, which lies behind, temporal.
forming nasal septum. this forms the spheno-palatine foramen. Laterally the section has passed through the inferior orbital fissure, which is continuous above with the pterygo-palatine fossa. Inferiorly the section passes through the line of fusion of the pterygoid processes with the pyramidal process of the palate
bone and the union of the latter with the maxilla. Just above this the opening of the pterygo-palatine canal, which leads from the pterygo-palatine fossa to the inferior surface of the hard palate, is visible; whilst inferiorly a small portion of the lower part of the
pterygoid fossa is cut through. Within the choanæ the middle and inferior conchæ are seen; the inferior border of the former corresponds to the level of the superior border of the zygomatic arch, whilst the attached edge of the latter to the perpendicular part of the palate lies in the same horizontal plane as the inferior margins of that arch. Note also that the medial pterygoid laminæ lie considerably within the lines of the medial surfaces of the alveolar border, and reach some little distance below the level of the hard palate.
The next section (Fig. 178) passes through the mandibular fossa just behind the tuberculum articulare; superiorly, it cuts the vault half an inch behind the bregma. The middle cranial fossa is shown in section, the floor of which descends as low as the level of the inferior surface of the body of the sphenoid, corresponding laterally to a horizontal plane passing through the superior edge of the posterior root of the zygoma.
The body of the sphenoid rises a finger's breadth above this in the median plane; the cavity within it is exposed, whilst on either side and below is seen the groove for the internal carotid artery, leading upwards from the medial part of the foramen lacerum, which is here divided. To the lateral side of the groove is seen the prominent edge of the lingula,
immediately below which is the Fig. 178.-FRONTAL SECTION OF THE SKULL PASSING THROUGH THE MANDIBULAR Fossa JUST BEHIND THE
TUBERCULUM ARTICULARE: posterior aperture of the pterygoid
canal, the inferior edge of which is 1. Crista galli of ethmoid. 15. Great wing of sphenoid in in part concealed by the pterygoid 2. Posterior clinoid process.
front of spine. 3. Optic foramen. 16. Foramen ovale.
tubercle. Immediately lateral to 4. Anterior clinoid process. 17. Lingula.
the foramen lacerum the foramen 5. Orbital part of frontal. 18. Anterior margin of foramen ovale is seen separated from the 6. Small wing of sphenoid. lacerum and opening of surface of the section by a narrow 7. Snture between squamous pterygoid canal.
part of the temporal, and 19. Postero - lateral margin of bridge of bone. Here it is seen to parietal bones.
lateral pterygoid lamina. overlie the root of the lateral ptery8. Superior orbital fissure. 20. Groove for carotid artery. goid lamina. The section passes 9. Cerebral surface of great 21. Pterygoid fossa.
just in front of the foramen spinwing of sphenoid.
22. Scaphoid fossa. 10. Foramen rotundum. 23. Hanulus of medial ptery. osum, and here is visible the stout 11. Squamous part of temporal. goid lamina.
suture between the great wing of 12. Posterior root of zygomatic 24. Inferior concha.
the sphenoid and the squamous part process.
25. Inferior meatus of the nose. of the temporal bone. The man13. Tuberculum articulare. 26. Nasal septum. 14. Mandibular fossa. 27. Opening of sphenoidalsinus.
dibular fossa of the temporal bone 28. Dorsum sellæ.
is cut on either side, and in its
deepest part is separated from the middle cranial fossa by but a thin lamina of bone. The thinness of the squamous part of the temporal and the manner in which it is sutured to the parietal is also well displayed.
The next figure (Fig. 179) displays the anterior surface of the section immediately behind that above described. In the centre is seen the body of the sphenoid, and the
posterior wall of the sinus is now exposed; on either side the apex of the petrous part of the : temporal abuts upon the side of the body of the sphenoid, and the large orifice of the carotid
canal is seen opening on to the posterior wall of the foramen lacerum, which is here divided. In the recess between the lateral wall of the carotid canal and the spine of the sphenoid is the groove leading into the osseous part of the auditory tube, in front of which the base is pierced by the foramen spinosum. Lateral to the angular spine, the mandibular fossa is divided and its thin roof displayed. Crossing it transversely is seen the petrotympanic fissure which divides the fossa into an articular and non-articular part. The floor of the middle cranial fossa is here seen to be formed by the upward slope of the anterior surface of the petrous part of the temporal, which is pierced by the hiatus canalis facialis, and the foramen for the lesser superficial petrosal nerve. On the upper surface of the summit of the petrous part of the temporal the depression for the lodgment of the semilunar ganglion is well seen on either side.
The last section, the anterior surface of which Fig. 180 is a representation, passes vertically through the base immediately in front of the root of the styloid process. In the Fig. 179.- ANTERIOR SURFACE OF THE SECTION OF THE SKULL median plane the basi-occipital is divided a little in front of the 1. Impressio trigemini on apex of 13. Angular spine of the sphenoid. anterior extremities of the oc- petrous bone.
14. Styloid process. cipital condyles ; its upper sur
2. Squamo-parietal suture. 15. Canal for auricular branch of the
3. Groove for posterior branch of vagus with opening of carotid face is concave from side to side middle meningeal artery.
canal in front and above it. and forms a wide groove for the 4. Eminence of superior semi. 16. Position of osseous opening of medulla oblongata and pons.
circular canal (eminentia auditory tube.
17. Jugular foramen. On either side there is a narrow
5. Hiatus facialis.
18. Medial wall of open carotid interval between the lateral edge 6. Posterior root of zygomatic canal. of the basi-occipital and the process of temporal.
19. Canalis hypoglossi. posterior border of the petrous 7. Leads into external acoustic 20. Condyle of occipital bone.
21. Petro-occipital suture. part of the temporal, which in
8. Mandibular fossa.
22. Posterior wall of sphenoidal life is occupied by dense fibrous 9. Tympanic plate.
sinus. tissue; running along the upper 10. Mastoid process.
23. Position of pharyngeal tubercle. surface of this suture is the in- 11. Leading into stylo-mastoid 24. Anterior margin of foramen ferior petrosal sinus. Laterally 12. Roof of carotid canal.
25. Occipital condyle. the section passes through the temporal bone, dividing the cavity of the tympanum and laying open the external acoustic meatus. To the medial side of the tympanic wall the cochlea is exposed, whilst above and lateral to it the canalis facialis is twice divided, the section passing posterior to the angle formed by its genu. Below the cochlea, and separated from it and the medial part of the floor of the tympanum, the carotid canal is in part exposed. Above the tympanum is the epitympanic recess ("attic") leading into the tympanic antrum, the whole being
15 16 17 18 19 20
21 22 23
roofed in by the thin tegmen tympani, which separates it from the middle cranial fossa. The obliquity of the medial end of the external acoustic meatus, together with the
groove for the attachment of the tympanic membrane, is well seen, and the thickness of the upper
wall of that passage is also noteworthy. The floor of the meatus, formed by the tympanic plate, which separates it from the mandibular fossa, is much thinner, but in the region of the root of the styloid process there is a massing together of dense bone.
Figure 181 represents a horizontal section passing through the face a little below the level of the inferior orbital margin, cutting through the root of each pterygoid process posteriorly. The nasal cavities and the maxillary sinuses are thus exposed. The nasal cavity is divided slightly below the inferior edge of the middle concha along the line of the middle meatus. The thin partition, which here separates the nose from the maxillary sinus, is cut through, and the aperture into the sinus laid open.
In front of this, the
canal for the naso-lacrimal duct 9 10 11 12
is cut across, and its relations Fig, 180.– VERTICAL SECTION THROUGH THE SKULL IMMEDIATELY to the maxillary sinus in front IN FRONT OF THE ROOT OF THE STYLOID PROCESS.
and to the lateral side, and 1. Cochlea.
10. Inferior opening of carotid to the nose medially, are well 2. Entrance to the antrum.
canal. 3. Sulcus tympanicus.
displayed. The form of the 11. Jugular foramen. 4. Tympanic bone. 12. Canalis hypoglossi.
maxillary sinus, as exposed, is 5. Tympano-mastoid fissure. 13. Occipital condyle.
triangular, the summit of the 6. Part of mandibular fossa. 14. Foramen magnum.
triangle being directed later7. Tympanic cavity (floor).
15. Basi-occipital. 8. Styloid process.
16. Squamous part of occipital ally towards the root of the 9. Jugular fossa.
zygomatic process. Its anterior
wall, which is here stout, is pierced obliquely by the infra-orbital canal which at this point reaches the facial surface of the maxilla at the infra-orbital foramen. Its posterior wall
, thin and convex backwards, is directed towards the infra-temporal fossa laterally, and to the pterygo-palatine fossa medially, where it lies in front of the pterygoid processes. The latter fossa has been cut across and is seen to correspond to the interval between the posterior and superior surface of the maxilla, and the anterior aspect of the root of the pterygoid process. Laterally, it is seen to communicate with the infra-temporal fossa by means of the pterygomaxillary fissure which is here cut across; medially, it opens into the nose by the sphenopalatine foramen, which is also divided. On one side the anterior orifice of the pterygoid canal is seen opening on to the posterior wall of the fossa. On the other side, the canal has been laid open, by removing its lower wall, so as to expose its whole length as it leads backward to the anterior edge of the foramen lacerum. In the middle line, the nasal septum, here formed by the vomer and perpendicular part of the ethmoid, is shown in section. A line passing through the inferior orbital fissures cuts the zygomatic arch where the zygomatic process of the temporal articulates with the zygomatic bone.