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.

3. Crista galli of ethmoid.

4. Cribriform plate of ethmoid.
5. Perpendicular part of eth-
moid, assisting in the forma-
tion of the nasal septum.
6. Labyrinth of ethmoid con-
sisting of the ethmoidal cells.
7. Lamina papyracea of ethmoid.
8. Middle meatus of nose.
9. Middle concha.

10. Opening from middle meatus into maxillary sinus.

11. Orbital surface of maxilla.

20.

21.

22.

22

20 19

FIG. 176.-FRONTAL SECTION PASSING INFERIORLY THROUGH

THE INTERVAL BETWEEN THE FIRST AND SECOND MOLAR TEETH.
The frontal and maxillary bones, where cut, are coloured blue;
the ethmoid, inferior concha, and zygomatic red; the vomer yellow.
1. Groove for sagittal sinus. 12. Zygomatico-frontal suture.
2. Crest for attachment of falx 13. Infra-orbital groove.
cerebri.

Maxillary sinus.

14. 15.

12

14

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 ethmoidal 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. 15 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 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 of the teeth sometimes project into the floor of the cavity.

The nasal cavities are narrow above, where they lie between the orbital cavities, from which they are separated by the cells within the labyrinth of the ethmoid. The roof which corresponds to the cribriform plate is narrow, and lies between the septum medially and the labyrinth on either side.

At the level of the orbital floor the nasal cavities expand laterally, the middle meatus running longitudinally in the angle formed 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

Canal for the anterior alveolar
nerve and vessels exposed.
Inferior concha.

Inferior meatus of nose.
Alveolar process of maxilla.
Groove for posterior palatine
nerve and greater palatine
vessels.

Palatine process of maxilla.

Maxillary crest forming part
Vomer forming part of nasal

of nasal septum.

septum.

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 fossæ 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 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.

2.

3.

4.

1. Depression for arach- 10.
noideal granulation.

Groove for sagittal sinus. 11.
Crista galli of ethmoid.
Opening of sphenoidal
sinus into superior
meatus of nose through
spheno- ethmoidal re-

cess.

5. Superior orbital fissure.
6. Part of middle fossa
formed by cerebral
surface of great wing
of sphenoid.
Zygomatic crest of great
wing of sphenoid.
8. Inferior orbital fissure.

9. Zygomatic process of
temporal.

12.
13.

14.

The nasal cavities, now much diminished in height, are roofed in above by the inferior surface of the body of the sphenoid and the alæ of the vomer, whilst the lateral walls are seen to be formed by the thin perpendicular parts of the palate bones, lateral to which the rounded posterior surface of the maxilla is directed backwards, here forming the anterior wall of the pterygo - palatine fossa- the space which lies between the anterior part of the pterygoid process behind and the maxilla anteriorly. As will be seen, the medial wall of this space is formed by the perpendicular part of the palate, which is, however, deficient above immediately below the inferior surface of the body of the sphenoid. In the in- 7. terval between the orbital process, which lies in front of the section, and the sphenoidal process, which lies behind, 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

Zygomatic process of maxilla.

Surface of maxilla which forms the anterior wall of the pterygo-palatine fossa.

Spheno-palatine foramen. Opening of pterygo-palatine canal.

Perpendicular part of
palate bone.
Pterygoid fossa.

Superior meatus of nose. 17. Middle meatus of nose.

15.
16.

18. Inferior meatus of nose.

19. Inferior concha.
20. Middle concha.

21. Maxillary crest and vomer
forming nasal septum.

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 concha 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 lamina 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 posterior aperture of the pterygoid canal, the inferior edge of which is in part concealed by the pterygoid tubercle. Immediately lateral to the foramen lacerum the foramen ovale is seen separated from the surface of the section by a narrow bridge of bone. Here it is seen to overlie the root of the lateral pterygoid lamina. The section passes just in front of the foramen spin

17. Lingula.

18. Anterior margin of foramen
lacerum and opening of
pterygoid canal.

20.

Postero-lateral margin of
lateral pterygoid lamina.
Groove for carotid artery.
21. Pterygoid fossa.
22. Scaphoid fossa.

23.

Hamulus of medial ptery- osum, and here is visible the stout goid lamina. suture between the great wing of 24. Inferior concha. the sphenoid and the squamous part 25. Inferior meatus of the nose. of the temporal bone. The man26. Nasal septum. 27. Opening of sphenoidal sinus. dibular fossa of the temporal bone 28. Dorsum sellæ. is cut on either side, and in its deepest part is separated from the The thinness of the squamous part of to the parietal is also well displayed.

2

1. Crista galli of ethmoid. 2. Posterior clinoid process. 3. Optic foramen.

4. Anterior clinoid process.
5. Orbital part of frontal.

6. Small wing of sphenoid.
7. Suture between squamous

part of the temporal, and

parietal bones.

8. Superior orbital fissure.

9. Cerebral surface of great wing of sphenoid.

10. Foramen rotundum.

11. Squamous part of temporal. 12. Posterior root of zygomatic

process.

13. Tuberculum articulare. 14. Mandibular fossa.

19.

27 26

25 24

FIG. 178.-FRONTAL SECTION OF THE SKULL PASSING THROUGH THE

MANDIBULAR FOSSA JUST BEHIND THE TUBERCULUM ARTICULARE.

middle cranial fossa by but a thin lamina of bone. the temporal and the manner in which it is sutured

1

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 5 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 median plane the basi-occipital is divided a little in front of the anterior extremities of the occipital condyles; its upper surface is concave from side to side and forms a wide groove for the medulla oblongata and pons. On either side there is a narrow interval between the lateral edge of the basi-occipital and the posterior border of the petrous part of the temporal, which in life is occupied by dense fibrous tissue; running along the upper surface of this suture is the in

2

2.

3.

1. Impressio trigemini on apex of 13.
petrous bone.
14.
15.

21 22 23

15 16 17 18 19 20 FIG. 179.-ANTERIOR SURFACE OF THE SECTION OF THE SKULL IMMEDIATELY BEHIND THE PRECEDING SECTION.

Squamo-parietal suture.

Groove for posterior branch of
middle meningeal artery.

4. Eminence of superior semi- 16.
circular canal (eminentia
arcuata).

5. Hiatus facialis.

6.

Angular spine of the sphenoid.
Styloid process.
Canal for auricular branch of the
vagus with opening of carotid
canal in front and above it.
Position of osseous opening of
auditory tube.

17. Jugular foramen.

18. Medial wall of open carotid
canal.

19. Canalis hypoglossi.
20. Condyle of occipital bone.
21. Petro-occipital suture.
22. Posterior wall of sphenoidal
sinus.

7.

meatus.

8. Mandibular fossa.
9. Tympanic plate.
10. Mastoid process.

11. Leading into stylo-mastoid
foramen.

ferior petrosal sinus. Laterally 12. Roof of carotid canal.
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

23. Position of pharyngeal tubercle. 24. Anterior margin of foramen

magnum.
25. Occipital condyle.

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.

HORIZONTAL SECTION.

1

1. Cochlea.

2. Entrance to the antrum.

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 is cut across, and its relations to the maxillary sinus in front and to the lateral side, and

10. Inferior opening of carotid to the nose medially, are well

canal.

displayed. The form of the maxillary sinus, as exposed, is triangular, the summit of the triangle being directed later

13. Occipital condyle.

14. Foramen magnum.
15. Basi-occipital.

16. Squamous part of occipital ally towards the root of the
zygomatic process. Its anterior
wall, which is here stout, is

bone.

3. Sulcus tympanicus.

4. Tympanic bone.

5. Tympano-mastoid fissure.

6. Part of mandibular fossa. 7. Tympanic cavity (floor). 8. Styloid process.

9. Jugular fossa.

9 10 11 12 13 14

FIG. 180.-VERTICAL SECTION THROUGH THE SKULL IMMEDIATELY
IN FRONT OF THE ROOT OF THE STYLOID PROCESS.

11. Jugular foramen.
12. Canalis hypoglossi.

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.