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expanded area, the vestibule; this is bounded laterally by the lateral crus of the greater alar cartilage, and medially by the lower part of the septum; it is prolonged as a small recess towards the apex of the nose. The vestibule is partly subdivided
Crus laterale ofgreater
by a curved ridge. It is lined with skin and, in its lower half, there are hairs and sebaceous glands; the hairs are curved downwards Crus mediale cartilage to guard the entrance to the nostril. The superior part of the vestibule is smooth, and is limited above and posteriorly by a slightly marked arched prominence, the limen nasi, beyond which the nasal cavity is lined with mucous membrane.
Lower edge of -cartilage of septum
Fatty tissue of
Each nasal cavity, above and behind the vestibule, is divided into a superior or olfactory, and an inferior or respiratory region. The olfactory region is a narrow
slit-like space; it comprises the middle of the superior nasal concha and the corresponding portion of the septum. The respiratory region includes the remaining part of the cavity.
Septum Nasi (Fig. 668). Where the bony septum of the nose is deficient, below and in front, the gap is filled by the septal cartilage. Until the seventh year the nasal septum lies, as a rule, in the median plane, but after this age it is very often bent to one or other side-more frequently to the right-the deflection being greatest usually along the line of junction of the vomer with the perpendicular lamina of
the ethmoid. De
flection of the septum is more common in Euro
pean than in nonEuropean skulls occurring about 53 per cent of the former and in about 28 per cent of the latter (Zuckerkandl). Associated with, or apart from, this deviation, crests or spurs of bone are found, projecting from the septum into one or other nasal cavity, in about 20 per cent of skulls. In the septum, a little above and in front of the naso-palatine recess, is a minute orifice, not always recognisable, from which a blind pouch extends upwards and backwards for a distance of from 2 to 9 mm. This is the vomero-nasal organ of Jacobson, and is supported by the vomero-nasal cartilage. In man this organ is rudimentary, but in many of the lower animals it is well developed (Fig. 673), and probably plays a part in the sense of smell, since it is lined with epithelium similar to that covering the olfactory region, and is supplied by branches of the olfactory nerve.
FIG. 672.-FRONTAL SECTION THROUGH NASAL CAVITIES; ANTERIOR HALF OF
Lateral Wall (Fig. 674). In the lateral wall of the nasal cavity, above the superior nasal concha, is a narrow, recess, the recessus sphenoethmoidalis, into the posterior
part of which the sphenoidal air-sinus opens. The superior meatus of the nose is a short oblique fissure, directed downwards and backwards, under cover of the superior nasal concha; into it the posterior ethmoidal cells open by one or more orifices. A small meatus, bounded superiorly by a concha suprema, frequently exists above the superior meatus. The narrow slit-like interval between the nasal septum and the medial surface of the middle nasal concha is named the olfactory cleft or sulcus.
The middle meatus, situated below and lateral to the middle nasal concha, is a roomy passage, and is continued forwards into a slightly depressed area, termed the atrium meatus nasi, which lies immediately above the vestibule. The atrium is limited superiorly and anteriorly by a low ridge, the agger nasi, the representative of the naso-turbinal found in many animals. When the middle nasal concha has been removed the lateral wall of the meatus is exposed. On it is seen a narrow semilunar cleft, the hiatus semilunaris, bounded above by a rounded elevation, the bulla ethmoidalis, and below by the sharp edge of the processus uncinatus of the
cartilages FIG. 673.-SECTION THROUGH NOSE OF A KITTEN,
showing position of the vomero-nasal organs.
FIG. 674.-VIEW OF THE LATERAL WALL OF THE NOSE-THE NASAL CONCHE HAVING BEEN REMOVED.
ethmoid. The size of the bulla varies with that of the middle ethmoidal cells, which are contained within it and which open on or near its upper surface. Through the hiatus semilunaris the middle meatus. opens into the infundibulum, a curved channel, limited above by the bulla ethmoidalis, and below by the lateral surface of the processus uncinatus. The anterior end of the infundibulum receives
the openings of the anterior ethmoidal cells, and, in rather more than fifty per cent of skulls, is continued upwards as the fronto-nasal duct into the frontal air-sinus; in the remainder it is shut off from the lower end of the fronto-nasal duct by the union of the anterior part of the bulla ethmoidalis with the upper end of the processus uncinatus, and the fronto-nasal duct then opens into the anterior part of the middle meatus. The ostium maxillare or opening of the maxillary sinus is placed below the bulla ethmoidalis, and is hidden by the lower end of the processus uncinatus; an accessory ostium is frequently seen in the middle meatus, above the posterior part of the inferior nasal concha.
The inferior meatus lies below the inferior nasal concha, under cover of the anterior part of which is the slit-like orifice of the naso-lacrimal duct (see p. 825).
The roof is very narrow, except at its posterior part, and is divisible into three portions, fronto-nasal, ethmoidal, and sphenoidal, in accordance with the bones which enter into its formation.
The floor is nearly horizontal from before backwards, and is formed by the palatine process of the maxilla and the horizontal part of the palatine bone. In it, close to the inferior margin of the septum and immediately over the incisive foramen, a slight depression, the naso-palatine recess, is sometimes seen; it is directed downwards and forwards for a short distance, and indicates the position of a communication which existed between the nasal and buccal cavities in early foetal life.
Membrana Mucosa Nasi. The nasal mucous membrane is thick, highly vascular, and firmly bound to the subjacent periosteum and perichondrium. It is continuous, through the choanæ, with the mucous lining of the nasal part of the pharynx; through the naso-lacrimal and lacrimal ducts, with the conjunctiva; and, through the apertures, leading into the air-sinuses, with the delicate lining of these cavities.
Throughout the respiratory region it is covered with columnar, ciliated epithelium, interspersed amongst which are goblet or mucin cells, whilst between the bases of the columnar cells smaller pyramidal cells are interpolated. It contains a freely anastomosing venous plexus, which in some parts, e.g. over the inferior nasal conchæ, forms a cavernous plexus. Many acinous glands, secreting a watery fluid. are embedded in it, and are especially large and numerous in the posterior halves of
Zone of oval
round nuclei Basal cells
the nasal cavities,
while in children Epithelium the mucous
of the olfac- tains a considertory glands able amount of
In the olfactory region the
brane is yellow ish in colour, more delicate, and is covered with non-ciliated columnar epithelium (Figs.
675, 676). Em
bedded in it are
numerous tubular and branched
glands, the olfactory glands, which are lined with polygonal cells and open by fine ducts on its free surface. The epithelium of the olfactory region consists of: (1) supporting cells, (2) olfactory cells, and (3) basal cells.
1. Supporting Cells.-The superficial parts of these cells are columnar in shape and contain fine granules of yellow pigment, whilst the deeper portions are continued
ry for some distance as attenuated or branched processes. These cells contain elliptical or oval nuclei, which are situated at the deep ends of the columnar parts of the cells, and form what is termed the zone of oval nuclei. In many animals the free surface of this columnar epithelium is covered by a thin limiting membrane.
2. Olfactory Cells. - These are bipolar nerve-cells, the central processes of which are continued as the axons of the olfactory nervefibres. They are homologous with the cells of the spinal ganglia, but
differ from them in that processes of
they retain their primitive position in the surface epithelium.
cell bodies are spindleshaped and are arranged in several rows between the deeper, attenuated parts of the supporting cells. Each consists of a large, spherical nucleus with a small amount of enveloping protoplasm;
Body of cell with nucleus
the nuclei form a layer of some thickness, termed the zone. of round nuclei. The peripheral process of each cell is rod-like, and extends between the columnar portions of the supporting cells as far as their free surfaces, where it pierces the external limiting membrane and divides into a number of fine hair-like processes, termed olfactory hairs. The central process is a delicate, beaded filament, and is continued upwards as the axon of an olfactory nerve-fibre.
3. Basal Cells.-These cells are branched, and lie on a basement membrane between the deep extremities of the supporting and olfactory cells.
Olfactory Nerves.-The fibres of the olfactory nerves are devoid of medullary sheaths, and arise, as stated, from the olfactory cells. They are collected into fasciculi which form a plexiform network under the mucous membrane and ascend on the medial and lateral walls of the olfactory region of the nasal cavity. They are lodged, near the base of the skull, in grooves or canals in the ethmoid bone and pass into the cranial cavity through the foramina in the lamina cribrosa of the ethmoid. Immediately above the lamina cribrosa they enter the olfactory bulb, in the glomerular layer of which they subdivide and form synapses with the dendrites. of the mitral cells of the bulb.
The trigeminal nerve supplies branches of ordinary sensation to the nasal mucous membrane as follows:-The septum is chiefly supplied by the naso-palatine nerve, but its posterior part receives some filaments from the spheno-palatine ganglion and from the nerve of the pterygoid canal, and its anterior portion from the naso-ciliary branch of the ophthalmic. The lateral wall is supplied (1) by the upper nasal branches of the nerve of the pterygoid canal and from the spheno-palatine ganglion; (2) by the lower nasal branches derived from the anterior palatine; and in front by (3) the naso-ciliary branch of the ophthalmic. The floor and anterior part of the inferior meatus are supplied by a nasal branch of the anterior superior alveolar nerve.
Blood-vessels.-Arteries. The chief artery of the nose is the spheno-palatine branch of the internal maxillary artery. This reaches the nasal cavity through the spheno-palatine foramen, and divides into (a) posterior nasal, which ramifies over the meatuses and concha and sends branches to the maxillary and frontal sinuses and the ethmoidal cells; and (b) naso-palatine, the artery of the septum. Twigs are given to the upper portion of the cavity by the anterior and posterior ethmoidal arteries, while its posterior part receives some small branches from the descending palatine. The nostrils are supplied by the lateral nasal branch of the external maxillary, and by
the septal artery from the superior labial. The maxillary sinus is partly supplied by the infra orbital artery, whilst the sphenoidal sinus gets its chief supply from the spheno-palatine artery. The veins form a dense cavernous plexus; this condition is well seen in the respiratory region, and especially so over the middle and inferior nasal concha and on the lower part of the septum The venous blood is carried in three chief directions, viz., anteriorly into the anterior facial vein, posteriorly into the spheno-palatine vein, and superiorly into the ethmoidal veins. The ethmoidal veins communicate with the ophthalmic veins and the veins of the dura mater; further, an ethmoidal vein passes up through the lamina cribrosa of the ethmoid, and opens either into the venous plexus of the olfactory bulb or directly into one of the veins on the orbital surface of the frontal lobe of the brain. The lymph vessels form an irregular network in the superficial part of the mucous membrane, and can be injected from the subdural or subarachnoid cavities. The larger vessels are directed posteriorly towards the choanæ, and are collected into two trunks, of which the larger passes to a lymph gland in front of the epistropheus, and the smaller to one or two lymph glands situated near the greater cornu of the hyoid bone.
The development of the nose is described in the section which deals with "General Embryology" (p. 50).
The bulb of the eye (O.T. eyeball) constitutes the peripheral part of the organ of sight; associated with it are certain accessory structures, such as the eyelids and the lacrimal apparatus.
OPTIC NERVE (x4).
Bulbus Oculi.—Situated in the anterior part of the orbital cavity, the bulb of the eye is protected in front by the eyelids, and is pierced behind by the optic nerve. which ramifies in its innermost tunic, the retina. The tendons of the ocular muscles are attached to the outer surface of the bulb, a short distance in front of