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angles, respectively; the superior angle is cut off by the cribriform plate; whilst the sides correspond to the frontal and nasal bones anteriorly, and the sphenoidal conchæ, sphenoidal process of the palate, and the ala of the vomer posteriorly. The cavity is therefore deep towards its middle, but gradually becomes shallower in front and behind where the piriform aperture and choana are situated. The piriform opening of the nose, which is of half-heart shape, is larger than that of the choanæ (O.T. posterior nares), and is directed forwards and downwards; the choanæ are of rhomboidal form, and slope backwards and downwards. The inferior meatus is the channel which is overhung by the inferior concha, and its floor is formed by the side-to-side concavity of the upper surface of the hard palate. Opening into it above, under cover of the anterior part of the inferior concha, is the canal for the naso-lacrimal duct; whilst its floor is pierced in front near the middle line by the canalis incisivus. The middle meatus is the hollow between the middle and inferior conchæ; it slopes from above downwards and backwards, and is overhung by the free curved edge of the middle concha, beneath which there is a passage called the infundibulum, leading upwards and forwards to open superiorly into the frontal sinus, as well as into some of the anterior ethmoidal cells. Under cover of the centre of the middle concha and continuous with the infundibulum in front there is a curved groove, the hiatus semilunaris, into which open one or more orifices from the maxillary sinus. Above this groove there is a rounded eminence, the bulla ethmoidalis, overlying the middle ethmoidal cells, which usually open on its surface. The superior meatus, about half the length of the middle meatus, is placed between the superior and middle conchæ in the posterior and upper part of the cavity; it receives the openings of the posterior ethmoidal cells. Near its posterior extremity the spheno-palatine foramen pierces its lateral wall, and brings it in relation with the pterygopalatine fossa. The sphenoidal sinus opens on the roof of the nose, above the level of the superior conchæ, into a depression called the spheno-ethmoidal recess.
Septum Nasi.-If the opposite half of the section in which the osseous nasal septum is retained be now studied, it will be seen to be formed by the crests of the maxillary and palate bones below, on which rests the vomer, the posterior border of which being free, forms the posterior edge of the nasal septum, which slopes obliquely upwards and backwards towards the inferior surface of the body of the sphenoid. Here the vomer articulates with the rostrum of the sphenoid. In front of this the vomer articulates with the perpendicular part of the ethmoid, and between them anteriorly there is an angular recess into which the cartilaginous septum fits. Superiorly and anteriorly the osseous septum is completed by the articulation of the perpendicular part of the ethmoid with the nasal spine of the frontal, together with the nasal crest formed by the union of the nasal bones; whilst posteriorly and superiorly the perpendicular plate of the ethmoid articulates with the median sphenoidal crest of the sphenoid. In most instances the osseous septum is not perfectly vertical, but is deflected towards one or other side.
Air-sinuses in Connexion with the Nasal Cavities.-Connected with the nasal cavities are a number of air-sinuses. These are found within the body of the sphenoid, the labyrinth of the ethmoid, the orbital process of the palate bone, the body of the maxilla, and the superciliary arch of the frontal bone.
The sphenoidal sinus, of variable size, occupies the interior of the body of the sphenoid. In some cases it extends towards the roots of the pterygoid processes. In front it is formed in part by the absorption of the sphenoidal conchæ and is divided up into two cavities by a sagittally placed partition, which, however, is frequently displaced to one or other side. It opens anteriorly into the roof of the nose in the region of the spheno-ethmoidal recess.
The ethmoidal sinuses are placed between the lateral aspects of the upper part of the nasal cavities, and the cavities of the orbits, from which they are separated by thin and papery walls. These air-spaces are completed by the articulation of the ethmoid with the maxilla, lacrimal, frontal, sphenoid, and palate bones, and are divided into three groups-an anterior, middle, and posterior. The latter communicates with the superior meatus; the anterior and middle open either independently or in conjunction with the infundibulum into the middle meatus.
The sinus in the orbital process of the palate bone either communicates with the sphenoidal sinus, or else assists in closing in some of the posterior ethmoidal cells. Its communication with the nasal cavity is through one or other of these spaces.
The maxillary sinus lies to the lateral side of the nasal cavity, occupying the body of the maxilla. Its walls, which are relatively thin, are directed upwards to the orbit, forwards to the face, backwards to the infra-temporal and pterygo-palatine fossæ, and medially to the nose. In the latter situation the perpendicular part
of the palate bone, the uncinate process of the ethmoid, the maxillary process of the inferior concha, and a small part of the lacrimal bone assist in the formation of the thin osseous partition which separates it from the nasal cavity. The floor corresponds to the alveolar border of the maxilla, and differs from the other walls in being stout and thick; it is, however, deeply pitted inferiorly by the alveoli for the teeth. The sinus opens by a narrow orifice in the floor of the hiatus semilunaris into the middle meatus. Occasionally there are two openings.
The frontal sinuses lie, one on either side, between the inner and outer tables of the frontal bone over the root of the nose, and extend laterally under the superciliary arches. The partition which separates them is usually central, though it may be deflected to one or other side. Each communicates with the nose through a passage called the infundibulum, which opens inferiorly into the anterior part of the corresponding middle meatus, below the ethmoidal bulla and continuous with the hiatus semilunaris.
Vomer of sphenoid
FIG. 174. THE NASAL SEPTUM AS SEEN FROM THE LEFT SIDE.
The frontal, maxillary, and sphenoid bones are coloured red; the nasal, vomer, and basi-occipital blue; the perpendicular part of the ethmoid and the horizontal part of the palate bone are left uncoloured.
The fact should not be overlooked that the air-spaces within the temporal bone, viz., the tympanic cavity and the mastoid air-cells, are brought into communication with the naso-pharynx through the auditory tubes. Further details regarding the air-sinuses and the mode of their growth will be found under the description of the individual bones.
The relations of many parts of the cranium are best displayed in a series of frontal (coronal) sections.
By sawing off a thin slice from the front of the lower part of the frontal bone above, and carrying the section downwards through the medial wall of the orbit and the frontal process of the maxilla, into the piriform aperture below, a number of important relations are revealed (see Fig. 175). In the frontal region the extent and arrangement of the frontal sinuses are displayed. The partition between the two sinuses, be it noted, is usually complete and central in position, though it may occasionally be perforated or oblique. The sinuses are hardly ever symmetrical, the right being usually the smaller of the two. (Logan Turner, Edin. Med. Journ. 1898.)
The infundibulum on either side, leading from the frontal sinus above to the middle
meatus below, is seen with the middle concha medial to it, and the anterior ethmoidal cells to its lateral side above. If the section passes through the canal for the nasolacrimal duct the continuity of that channel leading from the orbit above to the inferior meatus of the nose below is clearly shown. Its medial wall above, by which it is separated from the cavity of the nose, is formed by the thin lacrimal bone; below, it passes under cover of the inferior concha to open into the anterior part of the inferior meatus. It is
1. Frontal sinus.
2. Septum of frontal sinus deflected towards the right. 3. Infundibulum leading from sinus to middle meatus. 4. Anterior ethmoidal air-sinuses.
5. Middle concha.
FIG. 175.-PART OF THE FRONTAL, NASAL, AND MAXILLARY BONES REMOVED IN ORDER TO
DISPLAY THE RELATION OF THE VARIOUS CAVITIES EXPOSED.
The frontal and maxillary bones, where cut, are coloured blue; the ethmoid and the inferior concha red; the lacrimal and vomer yellow.
7. Cavity of maxillary sinus laid open.
9. Inferior meatus of nose.
10. Inferior concha.
11. Nasal septum.
Canal for naso-lacrimal duct laid open through-
separated from the maxillary sinus laterally by a thin lamina of bone. The cavity of the maxillary sinus is seen to extend upwards and forwards so as to pass over the lateral side as well as slightly in front of the canal for the naso-lacrimal duct.
The lower margins of the middle concha lie pretty nearly on a level with the most dependent parts of the orbital margins, whilst the lower borders of the inferior conchæ are placed a little above the lower margin of the piriform opening on a level with the lowest point of the zygomatico-maxillary suture.
Such a section will reveal any deflection of the nasal septum should it exist, and will also show that but a narrow cleft separates the upper part of the septum, on either side, from the medial surface of the superior concha.
The next section (Fig. 176) passes through the anterior part of the temporal fossa just
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.
10. Opening from middle meatus into maxillary sinus.
11. Orbital surface of maxilla.
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 conchæ, and zygomatic red; the vomer yellow. 1. Groove for sagittal sinus. 2. Crest for attachment of falx cerebri.
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 laby
rinth on either side.
12. Zygomatico-frontal suture.
Canal for the anterior alveolar
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
Palatine process of maxilla.
of nasal 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.
Superior orbital fissure. 6. Part of middle fossa
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 interval 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
14. formed by cerebral 15. surface of great wing 16. of sphenoid. 17. 18.
1. Depression for arach- 10. Zygomatic
Superior meatus of nose.
7. Zygomatic crest of great
19. Inferior concha.
20. Middle concha.
9. Zygomatic process of 21. Maxillary crest and vomer