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fuse at their lower edges, and by forward growth invade the posterior end of each anterior paraseptal cartilage, thus forming a deep groove in which the septal cartilage is lodged (Fawcett). As growth goes on the groove becomes reduced by the further fusion of the lateral plates and the absorption of the cartilage, until the age of puberty, by which time the lateral laminae have united to form a median plate, the primitively divided condition of which is now only represented by the eversion of the alæ and the grooving along the anterior border. According to Fawcett, the ossification of the Jacobsonian cartilage produces a hitherto undescribed element in the formation of the osseous nasal septum.
The nasal bones, two in number, lie in the interval between the frontal processes of the maxillæ, there forming the bridge of the nose. Each bone is of elongated quadrangular form, having two surfaces an inner and outer and four borders. The outer surface, somewhat constricted about its middle, is convex from side to side, and slightly concavo-convex from above downwards. Near its centre there is usually the opening of a nutrient canal.
Groove for internal
The inner surface is not so extensive as the outer, as the superior and anterior articular borders encroach somewhat upon it above. Concave from side to side, and also from above downwards, it is covered, in the recent condition, by the mucous membrane of the nose. Running downwards along this surface is a narrow groove (sulcus ethmoidalis) which transmits the anterior ethmoidal nerve. The anterior or medial border, thin below, is thick above, and, in conjunction with its fellow at the opposite side, with which it articulates, forms a median crest posteriorly, which is united to the spine of the frontal, the perpendicular plate of the ethmoid, and the septal cartilage of the nose, in that order from above downwards. The posterior or lateral border, usually the longest, is serrated and bevelled to fit on to the anterior edge of the frontal process of the maxilla. The superior border forms a wide toothed surface, which articulates with the medial part of the nasal notch of the frontal bone anteriorly; whilst, posteriorly, it rests in contact with the root of the nasal process of the same bone. The inferior border is thin and sharp, and is connected below with the lateral cartilage of the nose, and is usually deeply notched near its medial extremity.
THE RIGHT NASAL BONE.
A, Lateral side; B, Medial side.
Connexions. The nasal bone articulates with its fellow of the opposite side, with the frontal above, posteriorly with the perpendicular plate of the ethmoid and with the frontal process of the maxilla. It is also united to the septal and lateral cartilages of the nose.
Ossification. The nasal bones are each developed from a single centre, which makes its appearance, about the end of the second month, in the membrane covering the anterior part of the cartilaginous nasal capsule. Subsequent to birth the underlying cartilaginous stratum disappears, persisting, however, below in the form of the lateral nasal cartilage, and behind as the septal cartilage of the nose.
Ossa Suturarum (O.T. Wormian).
Along the line of the cranial sutures and in the region of the fontanelles, isolated bones of irregular form and variable size are occasionally met with. These are the once socalled Wormian bones, named after the Danish anatomist Wormius. They are now called ossa suturarum (sutural bones). Their presence depends on the fact that they are either developed from distinct ossific nuclei, or it may be from a division of the primary ossific deposit. Their occurrence may also be associated with certain pathological conditions
which modify the development of the bone. They usually include the whole thickness of the cranial wall, or they may only involve the outer or inner tables of the cranial bones. They are most frequent in the region of the lambda and the lambdoid suture. They occur commonly about the pterion, and in this situation are called epipteric bones (Flower). By their fusion with one or other of the adjacent bones they here lead to the occurrence of a fronto-squamosal suture. Their presence has also been noted along the line of the sagittal suture, and sometimes in metopic skulls in the inter-frontal suture. They are occasionally met with at the asterion and more rarely at the obelion. They appear less frequently in the face, but their presence has been noted around the lacrimal bone, and also at the extremity of the inferior orbital fissure, where they may form an independent nodule wedged in between the great wing of the sphenoid, the zygomatic, and the maxillary bones.
The bones of the face, seven in number, comprise two maxilla, two palates, two zygomatics, with the mandible or lower jaw.
The maxillæ, of which there are two, unite to form the upper jaw. Each consists of a body, with which are connected four projections, named respectively the zygomatic, frontal, alveolar, and palatine processes.
The body (corpus) is of pyramidal form, and contains within it a hollow called the maxillary sinus. It has four surfaces a facial or antero-lateral, an infratemporal or postero-lateral, an orbital or supero-lateral, and a nasal or medialand four processes-the malar, frontal, alveolar, and palatine.
Surfaces. The facies anterior (antero-lateral surface) is confluent below with the alveolar process. Above, it is separated from the orbital aspect by the margo infraorbitalis (infra-orbital margin), whilst medially it is limited by the free margin of the nasal notch, which ends below in the pointed spina nasalis anterior (anterior nasal spine). Posteriorly it is separated from the infra-temporal surface by
the inferior border of the zygomatic process. The facial aspect of the bone is ridged by the sockets of the teeth (juga alveolaria). The ridge corresponding to the root of the canine tooth is usually the most pronounced; medial to this, and overlying the roots of the incisor teeth, is the shallow incisive fossa, whilst placed laterally, on a higher level, is the deeper canine fossa, the floor of which is formed in part by the projecting zygomatic process. Above this, and near the infraorbital margin, is the infra-orbital foramen,
FIG. 157. THE RIGHT MAXILLA (Lateral View).
the external opening of the infra-orbital canal, which transmits the infra-orbital nerve and artery.
The infra-temporal or posterolateral surface is separated above from the orbital aspect by a rounded free edge, which forms the anterior margin of the inferior orbital fissure in the articulated skull. Inferiorly and anteriorly it is separated from the anterior surface
by the zygomatic process Ridge for middle,
and its free lower border.
tine fossæ. It is pierced in a downward direction by the apertures of the alveolar canals (foramina alveolaria), two or more in number, which transmit the corresponding nerves and vessels to the molar teeth. Its lower part, slightly more prominent where it overhangs the root of the third molar, is often called the tuber maxillare (maxillary tuberosity).
The planum orbitale (orbital surface), smooth and plane, is triangular in shape and forms part of the floor of the orbit. Its anterior edge corresponds to the infra-orbital margin; its posterior border coincides with the anterior boundary of the inferior orbital fissure. Its thin medial edge, which may be regarded as the base of the triangle, is notched in front to form the sulcus lacrimalis (lacrimal groove), behind which it articulates with the lacrimal bone for a short distance, then for a greater length with the lamina papyracea of the ethmoid, and terminates posteriorly in a surface for articulation with the orbital process of the palate bone. Its lateral angle corresponds to the base of the zygomatic process. Traversing its substance is the infra-orbital canal, the anterior opening of which has been already noticed on the anterior aspect of the body. Behind, however, owing to deficiency of its roof, the canal forms a groove which lips the edge of the bone which constitutes the anterior boundary of the inferior orbital fissure. If this canal be laid open, the orifices of the middle and anterior alveolar canals will be seen, which transmit the corresponding vessels and nerves to the premolar, canine and incisor teeth.
FIG. 158. THE RIGHT MAXILLA (Medial Aspect).
The facies nasalis (nasal surface) of the body is directed medially towards the nasal cavity. Below, it is confluent with the superior surface of the palatine process; anteriorly it is limited by the sharp edge of the nasal notch; above and anteriorly it is continuous with the medial surface of the frontal process; behind this it is deeply channelled by the lacrimal groove, which is converted into a canal by articulation with the lacrimal and inferior conchal bones. The channel so formed conveys the naso-lacrimal duct from the orbital cavity above to the inferior nasal meatus below. Behind this groove the upper edge of this area corresponds to the medial margin of the orbital surface, and articulates from before backwards with the lacrimal, lamina papyracea of the ethmoid, and the orbital process of the palate bone. The posterior border, rough for articulation with the palate bone, is traversed obliquely from above downwards and slightly medially by a groove, which, by articulation with the palate bone, is converted into the pterygo-palatine canal, which transmits
the greater palatine artery and anterior palatine nerve. Towards its upper and posterior part the nasal surface of the body displays the irregular, more or less triangular, opening of the maxillary sinus. This aperture which, in the articulated skull opens into the middle meatus of the nose, is much reduced in size by articulation with the lacrimal, ethmoid, palate, and inferior conchal bones. In front of the lacrimal groove the nasal surface is ridged horizontally by the crista conchalis (inferior conchal crest), to which the inferior conchal bone is attached. Below this the bone forms the lateral wall of the inferior nasal meatus, receiving the termination of the lacrimal groove. Above, and for some little distance also on the medial side of the frontal process, it constitutes the smooth lateral wall of the atrium of the middle meatus.
Processes. The processus zygomaticus (zygomatic process), which placed on the antero-lateral surface of the body, is confluent anteriorly with the facial surface of the body; posteriorly, where it is concave from side to side, with the infra-temporal surface; whilst superiorly, where it is rough and articular, it forms the apex of the triangular orbital surface, and supports the zygomatic bone. Inferiorly, its anterior and posterior surfaces meet to form an arched border, which fuses with the alveolar process opposite the root of the first molar tooth, and serves to separate the anterior from the infra-temporal surfaces of the body.
The processus frontalis (frontal process) arises from the upper and anterior part of the body. It has two surfaces-one lateral, the other medial. The lateral is divided into two by a vertical ridge (crista lacrimalis anterior), which is the upward extension of the infra-orbital margin. The narrow strip of bone behind this ridge is hollowed out, and leads into the lacrimal groove below. Posteriorly the edge of the frontal process here articulates with the lacrimal, and so forms the fossa for the lodgment of the lacrimal sac (fossa sacci lacrimalis). In front of the vertical crest, to which the medial palpebral ligament is attached, the lateral surface is confluent below with the facial surface of the body, and forms the side of the root of the nose. Here may often be seen a vascular groove entering the bone. Its anterior edge is rough, or grooved, for articulation with the nasal bone. Superiorly the summit of the process is serrated for articulation with the nasal notch of the frontal bone. The medial surface of the frontal process is directed towards the nasal cavity. It is crossed obliquely from below upwards and backwards by a ridge —the agger nasi or ethmoidal crest which is considered to be a vestige of the nasoturbinal which is met with in some mammals. Below this the bone is smooth and forms the upper part of the atrium of the middle meatus, whilst the ridge itself articulates posteriorly with the anterior part of the middle conchal bone, formed by the inferior concha of the ethmoid bone.
The processus alveolaris (alveolar process) projects from the inferior surface of the body of the bone below the level of the palatal process. Of curved form, it completes, with its fellow of the opposite side, the alveolar arch, in which are embedded, in sockets or alveoli, the roots of the teeth of the maxilla; ordinarily in the adult, when dentition is complete, each alveolar process supports eight teeth. Piercing the medial surface of the alveolar border behind the incisor teeth two small vascular foramina are usually visible. When any or all the teeth are shed the alveoli become absorbed, and the process may under these circumstances be reduced to the level of the plane of the palatine process. Posteriorly the alveolar process ends below the maxillary tuberosity of the body; anteriorly it shares in the formation of the intermaxillary suture.
The processus palatinus (palatine process), of the form of a quadrant, lies in the horizontal plane; it has two surfaces-superior and inferior-and three borders, a straight medial, a more or less straight posterior, and a curved lateral, by which latter it is attached to the medial side of the body and alveolar process as far back as the interval between the second and third molar teeth. Its inferior surface, together with that of its fellow, forms the anterior three-fourths of the vaulted hard palate; it is rough and pitted for the glands of the mucous membrane of the roof of the mouth, and is grooved, near the alveolar margin, by one or two channels which pass forward from the pterygo - palatine canal and transmit the
anterior palatine nerve and greater palatine artery. Its superior surface, smooth and concave from side to side, forms the floor of the corresponding nasal cavity. Its medial border, broad and serrated, rises in a ridge superiorly, so as to form with its fellow of the opposite side the nasal crest, which is grooved superiorly to receive the inferior border of the vomer. In front of its articulation with the vomer this ridge rises somewhat higher, being named the incisor crest, anterior to which it projects beyond the free border of the nasal notch, and together with its fellow forms the pointed projection called the anterior nasal spine. These parts support the septal cartilage of the nose. Immediately to the lateral side of the incisor crest the superior surface of the palatine process is pierced by a foramen which leads downwards, forwards, and a little medially, to open into a broad groove on the medial border of the bone immediately behind the central incisor tooth. When the two maxillæ are articulated, the two grooves form the oval foramen incisivum, into which the two afore-mentioned foramina open like the limbs of a Y; these are called the foramina of Stensen, and represent the channels by which in lower animals the organs of Jacobson open into the mouth. In man they afford a means of establishing an anastomosis between the vessels of the mouth and nose. In front and behind these, and lying within the fossa and in the line of the suture, are the smaller foramina of Scarpa, which transmit the naso-palatine nerves, the right nerve usually passing through the posterior foramen, the left through the anterior. The posterior border of the palatine process, which is sharp and thin, falls in line with the interval between the second and third molar, and articulates with the horizontal part of the palate bone.
Sinus Maxillaris. The maxillary sinus lies within the body of the bone, and is of corresponding pyramidal form, its base being directed towards the nasal cavity, with the middle meatus of which it communicates, its summit extending laterally into the root of the zygomatic process. It is closed in anteriorly, posteriorly, and above by the thin walls which form the anterior, infra-temporal, and orbital surfaces of the body. Inferiorly it overlies the alveolar process in which the molar teeth are implanted, more particularly the first and second, the sockets of which are separated from it by a thin layer of bone.
The angles and corners of this cavity are frequently groined by narrow ridges of bone, one superiorly corresponds to the relief formed by the infra-orbital canal. A vascular and nervous groove is often exposed, curving along the floor of the maxillary sinus just above the alveoli of the teeth. The interior of the cavity is lined by an extension from the mucous membrane of the nose.
Connexions. The maxilla articulates with the nasal, frontal, lacrimal, and ethmoid bones above, laterally with the zygomatic, and occasionally with the sphenoid, posteriorly and medially with the palate, whilst on its medial side it unites with its fellow of the opposite side, and also supports the inferior concha and the vomer.
Ossification.—The maxilla (proper) are developed in the connective tissue around the oral aperture of the embryo. Ossification commences in membrane from one centre in the neighbourhood of the canine tooth germ. From this centre growth takes place rapidly in several directions, viz., upwards on the lateral side of the nasal capsule to form the posterior part of the frontal process, backwards to form the zygomatic process, downwards to form the lateral wall of the alveolar process, and medially to form the palatine process. From the latter a process descends downwards on the medial side of the teeth to form the medial wall of the alveolar process. At first a large gap intervenes between the greater part of the palatine process and the zygomatic process, but bridges of bone ultimately connect the two, separating the various tooth germs, and so forming the tooth sockets. About the fourth month the maxilla invades a small lateral cartilaginous process of the nasal capsule (Mihalkovics), and incorporates it within itself. The infra-orbital nerve is at first placed considerably above the orbital surface of the maxilla, and only comes in contact with it in the second month when a groove is formed on the bone, which by the uprising of its lateral wall and its folding over medialwards finally encloses the nerve and forms the infra-orbital canal and foraThis account of the ossification of the maxilla, which differs considerably from that given in previous editions, is based on the work of Mall and Fawcett. In the early stages of the development of the bone the alveolar groove, in which the teeth are