DESCRIPTIVE AND SURGICAL ANATOMY

THE SKULL

 

BONES OF THE FACE.

The Facial Bones are fourteen in number, viz.:

• Two Nasal
• Two Palate
• Two Superior Maxillary
• Two Inferior Turbinated
• Two Lachrymal
• Vomer
• Two Malar
• Inferior Maxillary

NASAL BONES

The Nasal Bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper Dart of the face, formine bv their function the bridge of the nose. Each bone presents for examina­tion two surfaces, and four borders. Theoafer surface is concave from above downwards, con­vex from side to side, it is covered by the Compressor nasi mus­cle, marked by nu­merous small arterial furrows, and perforated about its centre by a foramen, sometimes rlnnhlp. for thfi transmission of a small vein. Sometimes this foramen is absent on one or both sides, and occasionally the foramen coecum opens on this surface. The inner surface is concave from side to side, convex from above downwards; in which direction it is traversed by a well marked longitudinal groove, sometimes a canal, for the passage of a branch of the nasal nerve. The superior border is narrow, thick, and serrated for articulation with the nasal notch of the frontal bone. The infe­rior border is broad, thin, sharp, directed obliquely downwards, outwards and backwards; serving for the attachment of the lateral cartilage of the nose. This border presents about its centre a notch, which transmits the branch of the nasal nerve above referred to, and is prolonged at its inner extremity into a sharp spine, which, when articulated with the opposite bone, forms the nasal angle. The external border is serrated, bevelled at the expense of the internal surface above, and of the external below, to articulate with the nasal process of the superior maxillary. The internal border, thicker above than below, articulates with its fellow of the opposite side, and is prolonged behind into a vertical crest, which forms part of the septum of the nose; this crest articulates with the nasal spine of the frontal above, and the perpendicular plate of the ethmoid below.

 

Nasal Bones

Development. By one centre for each bone, which appears about the same period as in the vertebrae.

Articulations. With four bones; two of the cranium, the frontal and ethmoid, and two of the face, the opposite nasal and the superior maxillary.

No muscles are directly attached to this bone.

SUPERIOR MAXILLARY BONE

The Superior Maxillary is one of the most important bones of the face in a surgical point of view, on account of the number of diseases to which some of its parts are liable. Its minute examination becomes, therefore, a matter of consi­derable importance. It is the largest bone of the face, excepting the lower jaw, and forms, by its union with its fellow of the opposite side, the whole of the up­per jaw. Each bone assists in the formation of three cavities, the roof of the mouth, the floor and outer wall of the nose, and the floor of the orbit; enters into the formation of two fossae, the zygomatic and spheno-maxillary, and two fissures, the spheno-maxillary, and pterygo-maxillary. Each bone presents for examination a body and four processes, malar, nasal, alveolar, and palatine.

The body is somewhat quadrilateral, and is hollowed out in its interior to form a large cavity, the antrum of Highmore. It presents for examination four sur­faces, an external or facial, a posterior or zygomatic, a superior or orbital, and an internal.

The external or facial surface is directed forwards and outwards. In the median line of the bone, just above the incisor teeth, is a depression, the incisive or myrtiform fossa, which gives origin to the Depressor labii superioris alseque nasi. Above and a little external to it, the Compressor naris arises. More external and immediately beneath the orbit, is another depression, the canine fossa, larger and deeper than the incisive fossa, from which it is separated by a vertical ridge, the canine eminence, corresponding to the socket of the canine tooth. The canine fossa gives origin to the Levator anguli oris. Above the canine fossa is the infra orbital foramen, the termination of the infra-orbital canal; it transmits the infra-orbital nerve and artery. Above the infra-orbital foramen is the margin of the orbit, which affords partial attachment to the Levator labii superioris proprius muscle.

The posterior or zygomatic surface is convex, directed backwards and outwards, and forms part of the zygomatic fossa. It presents about its centre two or three grooves leading to canals in the substance of the bone; they are termed the poste­rior dental canals, and transmit the posterior dental vessels and nerves. At the lower part of this surface is a rounded eminence, the maxillary tuberosity, especially prominent after the growth of the wisdom-tooth, rough on its inner side for articulation with the tuberosity of the palate bone. At the upper and inner part of this surface is the commencement of a groove, which, running down on the nasal surface of the bone, is converted into a canal by articulation with the palate bone, forming the posterior palatine canal.

Superior Maxillary Bone, Outer Surface

The superior or orbital surface is thin, smooth, irregularly quadrilateral, and forms part of the floor of the orbit. It is bounded internally by an irregular margin which articulates with three bones; in front, with the lachrymal; in the middle, with the os plan urn of the ethmoid; and behind, with the orbital process of the palate bone; posteriorly, by a smooth rounded edge which enters into the formation of the spheno-maxillary fissure, and which sometimes articulates at its anterior extremity with the orbital plate of the sphenoid; bounded externally by the malar process, and in front by part of the circumference of the orbit continuous, on the inner side, with the nasal, on the outer side, with the malar process. Along the middle line of this surface is a deep groove, the infra-orbital, for the passage of the infra-orbital nerve and artery. This groove commences at the middle of the posterior border of the bone, and, passing forwards, termiriates in a canal which subdivides into two branches; one of the canals, the infra-orbital, opens just below the margin of the orbit; the other, the smaller and most posterior one, runs in the substance of the anterior wall of the antrum; it is called the anterior dental, trans­mitting the anterior dental vessels and nerves to the front teeth of the upper jaw. The internal surface is unequally divided into two parts by a hori­zontal projection of bone, the palatine process; that portion above the palate-pro­cess forms part of the outer wall of the nose; the portion below it forms part of the cavity of the mouth. The superior division of this surface presents a large irregular shaped opening leading into the antrum of Highmore. At the upper border of this aperture are a number of broken cellular cavities, which, in the ar­ticulated skull, are closed in by the ethmoid and lachrymal bon'es. Below the aperture, is a smooth concavity which forms part of the inferior meatus of the nose, traversed by a fissure, the maxillary fissure, which runs from the lower part of the orifice of the antrum obliquely downwards and forwards, and receives the maxillary process of the palate. Behind it, is a rough surface which articulates with the perpendicular plate of the palate bone, traversed by a groove which, com-mencing near the middle of the posterior border, runs obliquely downwards and forwards, and forms, when completed by its articulation with the palate bone, the posterior palatine canal. In front of the opening in the antrum is a deep groove, converted into a canal by the lachrymal and inferior turbinated bones, and lodging the nasal duct. More anteriorly is a well marked rough ridge, the inferior turbi­nated crest, for articulation with the inferior turbinated bone. The concavity above this ridge forms part of the middle meatus of the nose, whilst that below it forms part of the inferior meatus. The inferior division of this surface is concave, rough and uneven, and perforated by numerous small foramina for the passage of nutrient vessels.

Superior Maxillary Bone, Inner Surface

The Antrum of Highmore, or Maxillary Sinus, is a large triangular-shaped cavity, hollowed out of the body of the maxillary bone; its apex, directed out­wards, is formed by the malar process; its base, by the outer wall of the nose. Its walls are everywhere exceedingly thin, its roof being formed by the orbital plate, its floor by the alveolar process, bounded in front by the facial surface, and behind by the zygomatic. Its inner wall, or base, presents, in the disarticulated bone, a large irregular aperture, which communicates with the nasal fossae. The margins of this aperture are thin and ragged, and the aperture itself is much con­tracted by its articulation with the ethmoid above, the inferior turbinated below, and the palate bone behind. In the articulated skull, this cavity communicates with the middle meatus of the nose generally by two small apertures left between the above-mentioned bones. In the recent state, usually only one small opening exists, near the upper part of the cavity, sufficiently large to admit the end of a probe, the rest being filled in by the lining membrane of the sinus.

Crossing the cavity of the antrum are often seen several projecting laminae of bone, similar to those seen in the sinuses of the cranium; and on its outer wall are the posterior dental canals, transmitting the posterior dental vessels and nerves to the teeth. Projecting into the floor are several conical processes, corresponding to the roots of the first and second molar teeth; in some cases, the floor is even per­forated by the teeth in this situation. It is from the extreme thinness of the walls of this cavity, that we are enabled to explain how tumours, growing from the antrum, encroach upon the adjacent parts, pushing up the floor of the orbit and displacing the eyeball, projecting inward into the nose, protruding forwards on to the cheek, and making their way backwards into the zygomatic fossa, and down­wards into the mouth.

The Malar Process is a rough triangular eminence, situated at the angle of separation of the facial from the zygomatic surface. In front, it is concave, forming part of the facial surface; behind, it is also concave, and forms part of the zygomatic fossa; superiorly, it is rough and serrated for articulation with the malar bone; whilst below, a prominent ridge, marks the division between the facial and zygomatic surfaces.

The Nasal Process is a thick triangular plate of bone, which projects upwards, inwards, and backwards, by the side of the nose, forming its lateral boundary. Its external surface is concave, smooth, perforated by numerous foramina, and gives attachment to the Levator labii superioris alaeque nasi, the Orbicularis palpebrarum, and Tendo oculi. Its internal surface forms part of the inner wall of the nares; it articulates above with the frontal, and presents a rough uneven surface which articulates with the ethmoid bone, closing in the anterior ethmoid cells; below this is a transverse ridge, the superior turbinated crest, for articulation with the middle turbinated bone of the ethmoid, bounded below by a smooth concavity, which forms part of the middle meatus; below this is the inferior turbinated crest (already de­scribed), for articulation with the inferior turbinated bone; and still more inferiorly, the concavity which forms part of the inferior meatus. The anterior border of the nasal process is thin, and serrated for articulation-with the nasal bone: its poste­rior border thick, and hollowed into a groove for the nasal duct; of the two margins of this groove, the inner one articulates with the lachrymal bone, the outer one forming part of the circumference of the orbit. Just where this border joins the orbital surface is a small tubercle, the lachrymal tubercle. This serves as a guide to the surgeon in the performance of the operation for fistula lachrymalis. The lachrymal groove in the articulated skull is converted into a canal by the lachrymal bone, and lachrymal process of the inferior turbinated; it is directed downwards, and a little backwards and outwards, is about the diameter of a goose-quill, slightly narrower in the middle than at either extremity, and lodges the nasal duct.

The Alveolar Process is the thickest part of the bone, broader behind than in front, and excavated into deep cavities for the reception of the teeth. These cavities are eight in number, and vary in size and depth according to the teeth they contain: those for the canine teeth being the deepest; those for the molars being widest, and subdivided into minor cavities; those for the incisors being single, but deep and narrow.

The Palate Process, thick and strong, projects horizontally inwards from the inner surface of the bone. It is much thicker in front than behind, and forms the floor of the nares, and the roof of the mouth. Its upper surface is concave from side to side, smooth, and forms part of the floor of the nose. In front is seen the upper orifice of the anterior palatine (incisor) canal, which leads into a fossa formed by the junction of the two superior maxillary bones, and situated imme­diately behind the incisor teeth. It transmits the anterior palatine vessels, the naso-pulatine nerves passing through the inter-maxillary suture. The inferior surface, also concave, is rough and uneven, and forms part of the roof of the mouth. This surface is perforated by numerous foramina for the passage of nutritious vessels, channelled at the back part of its aveolar border by a longi­tudinal groove, sometimes a canal, for the transmission of the posterior palatine vessels, and a large nerve, and presents little depressions for the lodgment of the pala­tine glands. This surface presents anteriorly the lower orifice of the anterior pala­tine fossa. The outer border is firmly united with the rest of the bone. The inner border is thicker in front than behind, raised above into a ridge, which, with the corresponding ridge in the opposite bone, forms a groove for the reception of the vomer. The anterior margin is bounded by the thin concave border of the opening of the nose, prolonged forwards internally into a sharp process, forming, with a similar process of the opposite bone, the anterior nasal spine. The pos­terior border is serrated for articulation with the horizontal plate of the palate bone.

Development of Superior Maxillary Bone

Development. This bone is formed at such an early period, and ossifi­cation proceeds in it with such rapidity, that it has been found impracticable hitherto to determine with accu­racy its number of centres. It appears, however, probable that it has four centres of develop­ment, viz., one for the nasal and facial portions, one for the orbital and malar, one for the incisive, and one for the palatal portion, in­cluding the entire palate except the incisive segment. The inci­sive portion is indicated in young bones by a fissure, which marks off a small segment of the palate, including the two incisor teeth. In some animals, this remains permanently as a separate piece, constituting the intermaxillary bone; and in the human subject, where the jaw is malformed, a detached piece is often found in this situation, most probably depending upon arrest of de­velopment of this centre. The maxillary sinus appears at an

earlier period than any of the other sinuses, its development commencing about the fourth month of foetal life.

Articulations. With nine bones; two of the cranium—the frontal and ethmoid, and with seven of the face, viz., the nasal, malar, lachrymal, inferior turbinated, palate, vomer, and its fellow of the opposite side. Sometimes it articulates with the orbital plate of the sphenoid.

Attachment of Muscles. Orbicularis palpebrarum, Obliquus inferior oculi, Leva-tor labii superioris alaeque nasi, Levator labii superioris proprius, Levator anguli-oris, Compressor naris, Depressor alae nasi, Masseter, Buccinator.

THE LACHRYMAL BONES

The Lachrymal are the smallest and most fragile of all the bones of the face, situated at tne iront part 01 tne inner wan 01 me orbit, and resemble somewhat in form, thinness, and size, a finger-nail; hence they are termed the ossa unguis.

Lachrymal Bones

Each bone presents for examination, two surfaces and four borders. The external or orbital surface is divided by a vertical ridge into two parts. The portion of bone in front of this ridge presents a smooth, concave, longitu­dinal groove, the free margin of which unites with the nasal process of the superior maxillary bone, completing the lachrymal groove. The upper part of this groove lodges the lachrymal sac; the lower part is continuous with the lachrymal canal, and lodges the nasal duct. The portion of bone be­hind the ridge is smooth, slightly concave, and forms part of the inner wall of the orbit. The

ridge, and part of the orbital surface immediately behind it, affords attachment to the Tensor tarsi: it terminates below in a small hook-like process, which articu­lates with the lachrymal tubercle of the superior maxillary bone, and completes the upper orifice of the lachrymal canal. It sometimes exists as a separate piece, which is then called the lesser lachrymal bone. The internal or nasal surface presents a depressed furrow, corresponding to the elevated ridge on its outer surface. The surface of bone in front of this forms part of the middle meatus; and that behind it articulates with the ethmoid bone, filling in the anterior ethmoidal cells. Of the four borders, the anterior is the longest, and articulates with the nasal process of the superior maxillary bone. The posterior, thin and uneven, articulates with the os planum of the ethmoid. The superior border, the shortest and thickest, articulates with the internal angular process of the frontal bone. The inferior is divided by the lower edge of the vertical crest into two parts, the posterior articulating with the orbital plate of the superior maxillary bone; the anterior portion being prolonged downwards into a pointed process, which articulates with the lachrymal process of the inferior turbinated bone, assisting in the formation of the lachrymal canal.

Development. By a single centre, which makes its appearance soon after ossi­fication of the vertebrae has commenced.

Articulations. With four bones; two of the cranium, the frontal and ethmoid, and two of the face, the superior maxillary and the inferior turbinated.

Attachment of Muscles. The Tensor tarsi.

THE MALAR BONES

The Malar are two small quadrangular bones, situated at the upper and outer part of the face, forming the prominence of the cheek, part of the outer wall and floor of the orbit, and part of the tem­poral and zygomatic fossae. Each bone presents for examination an external and an internal surface; four processes, the frontal, orbital, maxillary, and zygomatic; and four borders.

Malar Bones

The external surface is smooth, convex, perforated near its centre by one or two small apertures, the malar canals, for the passage of small nerves and vessels, covered by the Orbicularis pal pebrarum mus­cle, and affords attachment to the Zygomaticus major and minor muscles.

The internal surface, directed backwards and inwards, is concave, presenting internally a rough triangular surface, for articulation with the superior maxillary bone; and externally, a smooth concave surface, which forms the anterior boundary of the tem­poral fossa above, wider below, where it forms part of the zygomatic fossa. This surface presents a little above its centre the aperture of one or two malar canals, and affords attachment to part of two muscles, the temporal above, and the masseter below. Of the four processes, the frontal is thick and serrated, and articulates with the external angular process of the frontal bone. The orbital process is a thick and strong plate, which projects backwards from the orbital margin of the bone. Its upper surface, smooth and concave, forms, by its junction with the great ala of the sphenoid, the outer wall of the orbit. Its under surface, smooth and convex, forms part of the temporal fossa. Its anterior margin is smooth and rounded, forming part of the circumference of the orbit. Its superior margin, rough, and verted into a canal by its articulation with the tuberosity of the superior maxil­lary bone, and forming the posterior palatine canal. Near this groove, the orifices of one or two small canals, accessory posterior palatine, may frequently be seen. The anterior border is serrated, bevelled at the expense of its inferior surface, and articulates with the palate process of the superior maxillary bone. The posterior border is concave, free, and serves for the attachment of the soft palate. Its inner extremity is sharp and pointed, and when united with the opposite bone, forms a projecting process, the posterior nasal spine, for the attachment of the Azygos uvulae. The external border is united with the lower part of the perpen­dicular plate almost at right angles. The internal border, the thickest, is serrated for articulation with its fellow of the opposite side; its superior edge is raised into a ridge, which, united with the opposite bone, forms a groove, in which the vomer is received.

The Vertical Plate is thin, of an oblong form, and directed upwards and a little inwards.

The internal surface pre­sents at its lower part a broad shallow depression, which forms part of the lateral boundary of the in­ferior meatus. Immediately above this is a well marked horizontal ridge, the infe­rior turbinated crest, for the articulation of the in­ferior turbinated bone; above this, a second broad shallow depression may be seen, which forms part of the lateral boundary of the middle meatus, sur­mounted above by a hori­zontal ridge, less prominent than the inferior, the superior turbinated crest, for the articulation of the middle turbinated bone. Above the superior turbinated crest is a narrow horizontal groove, which forms part of the superior meatus. The external surface is rough and irregular throughout the greater part of its extent, for articulation with the inner surface of the superior maxillary bone, its upper and back part being smooth where it enters into the formation of the zygomatic fossa; it is also smooth in front, where it covers the orifice of the antrum. This surface presents towo'ds its back part a deep groove, converted into a canal, the posterior palatine, by its articulation with the superior maxillary bone. It transmits the posterior pala­tine vessels and a large nerve. The anterior border is thin, irregular, and presents opposite the inferior turbinated crest, a pointed projecting lamina, the maxillary process of the palate bone, which is directed forwards, and closes in the lower and back part of the opening of the antrum, being received into a fissure that exists at the inferior part of this aperture. The posterior border presents a deep groove, the edges of which are serrated for articulation with the ptery-goid process of the sphenoid. At the lower part of this border is seen a pyramidal process of bone, the pterygoid process or tuberosity of the palate, which is received into the angular interval between the two pterygoid plates of the sphenoid at their inferior extremity. This process presents at its back part three grooves, a median and two lateral ones. The former is smooth, and forms part of the pterygoid fossa, affording attachment to the Internal pterygoid muscle;whilst the lateral grooves are rough and uneven, for articulation with the anterior border of each pterygoid plate. The base of this process, continuous with the horizontal portion of the bone, presents the apertures of the accessory descending palatine canals; whilst its outer surface is rough, for articulation with the inner surface of the body of the superior maxillary bone. The superior border of the vertical plate presents two well marked processes, separated by an intervening notch or foramen. The anterior,or larger,is called the orbital process; the posterior, the sphenoidal. The Orbital Process, directed upwards and outwards, is placed on a higher level than the sphenoidal. It presents five surfaces, which enclose a hollow cellular cavity, and is connected to the perpendicular plate by a narrow constricted neck. Of these five surfaces, three are articular, two non-articular, or free surfaces. The three articu­lar are the anterior or maxillary surface, which is directed for­wards, outwards, and downwards, is of an oblong form, and rough for articulation with the superior maxillary bone. The posterior or sphenoidal surface, is directed backwards, upwards, and inwards. It ordinarily presents a small half-cellular cavity which communicates with the sphenoidal sinus, and the margins of which are serrated for articulation with the vertical part of the sphenoidal turbinated bone. The internal or ethmoidal surface is directed inwards, upwards and forwards, and articulates with the lateral mass of the ethmoid bone. In some cases, the cellular cavity above-mentioned opens on this surface of the bone, it-then commu­nicates with the posterior ethmoidal cells. More rarely it opens on both surfaces, and then communicates with the posterior ethmoidal cells, and the sphenoidal sinus. The non-articular or free surfaces of the orbital process are the superior or orbital, directed upwards and outwards, of a triangular form, concave, smooth, articulating with the superior maxillary bone, and forming the back part of the floor of the orbit. The external or zygomatic surface, directed outwards, back­wards and downwards, is of an oblong form, smooth, and forms part of the zygomatic fossa. This surface is separated from the orbital by a smooth rounded border, which enters into the formation of the spheno-maxillary fissure.

Left Plate Bone

The Sphenoidal Process of the palate bone is a thin compressed plate, much smaller than the orbital, and directed upwards and inwards. It presents three surfaces and two borders. The superior surface, the smallest of the three, articu­lates with the horizontal part of the sphenoidal turbinated bone; it presents a groove which contributes to the formation of the pterygo-palatine canal. The internal surface is concave, and forms part of the outer wall of the nasal fossa. The external surface is divided into two parts, an articular, and a non-articular portion; the non-articular portion is smooth and free, forming part of the zygo­matic fossa, whilst behind is a rough surface for articulation with the inner surface of the pterygoid process of the sphenoid. The anterior border forms the posterior boundary of the spheno-palatine foramen. The posterior border, serrated at the expense of the outer table, articulates with the internal surface of the pterygoid process.

Sometimes the two processes are united above, and form between them a complete foramen, or the notch is crossed by one or more spiculae of bone, so as to form two or more foramina. In the articulated skull, this foramen opens into the back part of the outer wall of the superior meatus, and transmits the spheno-palatine vessels and nerves.

Development. From a single centre, which makes its appearance at the angle of junction of the two plates of the bone. From this point ossification spreads; in­wards, to the horizontal plate; downwards, into the tuberosity; and upwards, into the vertical plate. In the foetus, the horizontal plate is much longer than the vertical; and even after it is fully ossified, the whole bone is remarkable for its shortness.

Articulations. With seven bones; the sphenoid, ethmoid, superior maxillary, inferior turbinated, vomer, opposite palate, and sphenoidal turbinated.

Attachment of Muscles. The Tensor palati, Azygos uvulae, Internal and External pterygoid.

THE INFERIOR TURBINATED BONES

The Inferior Turbinated bones are situated one on each side of the outer wall of the nasal fossae. Each bone consists of a layer of thin 'spongy' bone, curled upon itself like a scroll, hence its name 'turbinated;' and extending horizontally across the outer wall of the nasal fossa, immediately below the orifice of the antrum. Each bone presents two surfaces, two borders, and two extremities.

The internal surface is convex, perforated by numerous apertures, and traversed by longitudinal grooves and canals for the lodgment of arteries and veins. In the recent state it is covered by the lining membrane of the nose. The external surface is concave, and forms part of the inferior meatus. Its upper border is thin, irregular, and connected to various bones along the outer wall of the nose. It may be divided into three por­tions; of these, the anterior articu­lates with the inferior turbinated crest of the superior maxillary bone; the posterior with the inferior turbinated crest of the palate bone; the middle portion of the superior border presents three well marked processes, which vary much in their size and form. Of these the anterior and smallest, is situated at the junction of the anterior fourth with the posterior three-fourths of the bone; it is small and pointed, and is called the lachrymal process, for it articulates with the anterior inferior angle of the lachrymal bone, and by its margins, with the groove on the back of the nasal process of the superior maxillary, and thus assists in forming the lachrymal canal. At the junction of the two middle fourths of the bone, but encroaching on the latter, a broad thin plate, the ethmoidal process, ascends to join the unciform process of the ethmoid; from the lower border of this process, a thin lamina of bone curves downwards and outwards, hooking over the lower edge of the orifice of the antrum, which it narrows below; it is called the maxillary process, and fixes the bone firmly on to the outer wall of the nasal fossa. The inferior border is free, thick and cellular in structure, more especially in the centre of the bone. Both extremities are more or less narrow and pointed. If the bone is held so that its outer concave surface is directed backwards (i.e., towards the holder), and its superior border, from which the lachrymal and ethmoidal processes project, upwards, the lachrymal process will be directed to the side to which the bone belongs.

Inferior Turbinated Bone

Development. By a single centre which makes its appearance about the middle of foetal life.

Articulations. With four bones; one of the cranium, the ethmoid, and three of the face, the superior maxillary, lachrymal and palate.

No muscles are attached to this bone.

THE VOMER

The Vomer is a single bone, situated vertically at the back part of the nasal fossae, and forming part of the septum of the nose. It is thin, somewhat like a ploughshare in form, but it varies in different individuals, being frequently bent to one or the other side; it presents for examination two surfaces and four borders.

Vomer

The lateral surfaces are smooth, marked with small furrows for the lodgment of blood-vessels, and by a groove on each side, sometimes a canal, the naso-palatine, which runs obliquely downwards and forwards to the intermaxillary suture between the two ante­rior palatine canals; it trans­mits the naso-palatine nerve. The superior border, the thickest, presents a deep groove, bounded on each side by a horizontal projecting ala of bone; the groove receives the rostrum of the sphenoid, whilst the alas are over­lapped and retained by laminae which project from the under surface of the body of the sphenoid at the base of the pterygoid processes. At the anterior part of the groove a fissure is left for the transmission of blood-vessels to the substance of the bone. The inferior border, the longest, is broad and uneven in front, where it arti­culates with the two superior maxillary bones; thin and sharp behind where it joins with the palate bones. The upper half of the anterior border usually pre­sents two laminae of bone, which receive between them the perpendicular plate of the ethmoid, the lower half consisting of a single rough edge, also occasionally channelled, which is united to the triangular cartilage of the nose. The posterior border is free, concave, and separates the nasal fossae from one another behind. It is thick and bifid above, thin below.

Development. The vomer at an early period consists of two lamina united below, but separated above by a very considerable interval. Ossification commences in it at about the same period as in the vertebrae.

Articulations. With six bones; two of the cranium, the sphenoid and ethmoid; :and four of the face, the two superior maxillary, the two palate bones, and with the cartilage of the septum.

The vomer has no muscles attached to it. PREVIOUS PAGE  NEXT PAGE