-> Most of the facial skeleton is formed by nine bones: four paired (nasal, zygomatic, maxilla, and palatine) and one unpaired (mandible).
-> The calvaria of the new-born infant is large compared with the relatively small fascial skeleton.
-> This results from the small size of the jaws and the almost complete absence of the maxillary and other paranasal sinuses in the new-born skull.
-> These sinuses form large spaces in the adult facial skeleton. As the teeth and sinuses develop during infancy and childhood, the facial bones enlarge.
-> The growth of the maxillae between the ages of 6 and 12 years accounts for the vertical elongation of the child’s face.

The Nasal Bones 

-> These bones may be felt easily because they form the bridge of the nose.
-> The right and left nasal bones articulate with each other at the internasal suture.
-> They also articulate with the frontal bones, the maxillae, and the ethmoid bones.
-> The mobility of the anteroinferior portion of the nose, supported only by cartilages, serves as a partial protection against injure (e.g., a punch in the nose). However, a hard blow to the anterosuperior bony portion of the nose may fracture the nasal bones (broken nose).
-> Often the bones are displaced sideways and/or posteriorly.

The Maxillae 

-> The skeleton of the face between the mouth and the eyes is formed by the two maxillae.
-> They surround the anterior nasal apertures and are united in the medial plane at the intermaxillary suture to form the maxilla (upper jaw).
-> This suture is also visible in the hard palate, where the palatine processes of the maxillae unite.
-> Each adult maxilla consists of: a hollow body that contains a large maxillary sinus; a zygomatic process that articulates with its mate on the other side to form most of the hard palate; and alveolar processes that form sockets for the maxillary (upper) teeth.
-> The maxillae also articulate with the vomer, lacrimal, sphenoid, and palatine bones.
-> The body of the maxilla has a nasal surface that contributes to the lateral wall of the nasal cavity; an orbital surface that forms most of the floor of the orbit; an infratemporal surface that forms the anterior wall of the infratemporal fossa; and an anterior surface that faces partly anteriorly and partly anterolaterally and is covered buy facial muscles.
-> The relatively large infraorbital foramen, which faces inferomedially, is located about 1 cm inferior to the infraorbital margin; it transmits the infraorbital nerve and vessels.
-> The incisive fossa is a shallow concavity overlying the roots of the incisor teeth, just a shallow concavity overlying the roots of the incisor teeth, just inferior to the nasal cavity. This fossa is the injection site for anaesthesia of the maxillary incisor teeth.
-> If infected maxillary teeth are removed, the bone of the alveolar processes of the maxillae begins to be reabsorbed. As a result, the maxilla becomes smaller and the shape of the face changes.
-> Owing to absorption of the alveolar processes, there is a marked reduction in the height of the lower face, which produces deep creases in the facial skin that pass posteriorly from the corners of the mouth.

The Mandible 

-> This is a U-shaped bone and forms the skeleton of the lower jaw and the inferior part of the face. It is the largest and strongest facial bone.
-> The mandibular (lower) teeth project superiorly from their sockets in the alveolar processes.
-> The mandible (L. mandere, to masticate) consists of two parts: a horizontal part called the body, and two vertical oblong parts, called rami.
-> Each ramus ascends almost vertically from the posterior aspect of the body.
-> The superior part of the ramus has two processes: a posterior condylar process with a head or condyle and a neck, and a sharp anterior coronoid process.
-> The condylar process is separated from the coronoid process by the mandibular notch, which forms the concave superior border of the mandible.
-> Viewed from the superior aspect, the mandible is horseshoe-shaped, whereas each half is L-shaped when viewed laterally.
-> The rami and body meet posteriorly at the angle of the mandible.
-> Inferior to the second premolar tooth on each side of the mandible is a mental foramen (L. mentum, chin) for transmission of the mental vessels and the mental nerve.
-> In the anatomical position, the rami of the mandible are almost vertical, except in infants and in edentulous (toothless) adults.
-> On the internal aspect of the ramus, there is a large mandibular foramen.
-> It is the oblong entrance to the mandibular canal that transmits the inferior alveolar vessels and nerve to the roots of the mandibular teeth.
-> Branches of these vessels and the mental nerve emerge from the mandibular canal at the mental foramen.
-> Running inferiorly and slightly anteriorly on the internal surface of the mandible from the mandibular foramen is a small mylohyoid groove (sulcus), which indicates the course taken by the mylohyoid nerve and vessels.
-> These structures arise from the inferior alveolar nerve and vessels, just before they enter the mandibular foramen.
-> The internal surface of the mandible is divided into two areas by the mylohyoid line, which commences posterior to the third molar tooth. -> Just superior to the anterior end of the mylohyoid line are two small, sharp mental spines (genial tubercles), which serve as attachments for the genioglssus muscles.

The Zygomatic Bones 

-> The prominences of the cheeks (L. mala), the anterolateral rims and much of the infraorbital margins of the orbits, are formed by the zygomatic bones (malar bones, cheekbones).
-> They articulate with the frontal, maxilla, sphenoid, and temporal bones.
-> The frontal process of the zygomatic bone passes superiorly, where it forms the lateral border of the orbit (eye socket) and articulates with the frontal bone at the lateral edge of the supraorbital margin.
-> The zygomatic bones articulate medially with the greater wings of the sphenoid bone. The site of their articulation may be observed on the lateral wall of the orbit.
-> On the anterolateral aspect of the zygomatic bone near the infraorbital margin is a small zygomaticofacial foramen for the nerve and vessels of the same name.
-> The posterior surface of the zygomatic bone near the base of its frontal process is pierced by a small zygomaticotemporal foramen for the nerve of the same name.
-> The zygomaticofacial and zygomaticotemporal nerves, leaving the orbit through the previously named foramina, enter the zygomatic bone through small zygomaticoorbital foramina that pierces it orbital surface.
-> The temporal process of the zygomatic bone unites with the zygomatic process of the temporal bone to form the zygomatic arch.
-> This arch can be easily palpated on the side of the head, posterior to the zygomatic prominence (malar eminence) at the inferior boundary of the temporal fossa (temple).
-> The zygomatic arches form one of the useful landmarks for determining the location of the pterion. These arches are especially prominent in emaciated persons.
-> A horizontal plane passing medially from the zygomatic arch separates the temporal fossa superiorly from the infratemporal fossa inferiorly.

Other Bones

There are several other, very important bones in the skull, including the palatine bone, ethmoid bone, vomer, inferior concha and the ossicles of the ear (malleus, incus and stapes). These, however, are covered to greater detail where they are relevant in the head (e.g., ethmoid bone with the orbit and nasal cavity).

• Bones begin to form during the eighth week of embryomic life in the fibrous membranes (intramembranous ossification) and hyaline cartilage (endochondral ossification)

BONE

 A rigid form of CT, Consists of matrix and cells

 Matrix contains:

 organic component 35% collagen fibres

 inorganic salts 65% calcium phosphate (58,5%),  calcium carbonate (6,5%)

2 types of bone - spongy (concellous)

 compact (dense)

 Microscopic elements are the same

 Spongy bone consists of bars (trabeculae) which branch and unite to form a meshwork

 Spaces are filled with bone marrow

 Compact bone appears solid but has microscopic spaces

 In long bones the shaft is compact bone

 And the ends (epiphysis) consists of spongy bone covered with compact bone

Flat bones consists of 2 plates of compact bone with spongy bone in-between

 Periosteum covers the bone

 Endosteum lines marrow cavity and spaces

 These 2 layers play a role in the nutrition of bone tissue

 They constantly supply the bone with new osteoblasts for the repair and growth of bone

Microscopically

 The basic structural unit of bone is the Haversian system or osteon

 An osteon consists of a central Haversian canal

- In which lies vessels nerves and loose CT

- Around the central canal lies rings of lacunae

- A lacuna is a space in the matrix in which lies the osteocyte

- The lacunae are connected through canaliculi which radiate from the lacunae

- In the canaliculi are the processes of the osteocytes

- The canaliculi link up with one another and also with the Haversian canal

- The processes communicate with one another in the canaliculi through gap junctions

- Between two adjacent rows of lacunae lie the lamellae, 5-7µm thick

- In three dimensions the Haversian systems are cylindrical

- The collagen fibres lie in a spiral in the lamellae

- Perpendicular to the Haversian canals are the Volkman's canals

- They link up with the marrow cavity and the Haversian canals

- Some lamellae do not form part of a Haversian system

- They are the:

- Inner circumferential lamellae - around the marrow cavity

- Outer circumferential lamellae - underneath the outer surface of the bone

- Interstitial lamellae - between the osteons

Endosteum

Lines all cavities like marrow spaces, Haversian- and Volkman's canals

Consists of a single layer of squamous osteoprogenitor cells with a thin reticular CT layer underneath it

Continuous with the inner layer of periosteum

Covers the trabeculae of spongy bone

Cells differentiate into osteoblasts (like the cells of the periosteum)

Periosteum

 Formed by tough CT

 2 layers

Outer fibrous layer:  Thickest, Contains collagen fibres,

Some fibres enter the bone - called Sharpey's fibres

Contains blood vessels.

Also fibrocytes and the other cells found in common CT

Inner cellular layer

Flattened cells (continuous with the endosteum)

Can divide and differentiate into osteoprogenitor cells

spindle shaped

little amount of rough EPR

poorly developed Golgi complex

play a prominent role in bone growth and repair

Osteoblasts

Oval in shape, Have thin processes, Rough EPR in one part of the cell (basophilic)

On the other side is the nucleus, Golgi and the centrioles in the middle, Form matrix

Become trapped in the matrix

Osteocytes

Mature cells, Less basophilic than the osteoblasts, Lie trapped in the lacunae, Their processes lie in the canaliculi, Processes communicate with one another through gap junctions, Substances (nutrients, waste products) are passed on from cell to cell

Osteoclasts

 Very large,  Multinucleate (up to 50),  On inner and outer surface of bone,  Lie in depressions on the surface called Howships lacunae,  The cell surface facing the bone has short irregular processes

Acidophylic

 Has many lysosomes, polyribosomes and rough EPR

 Lysosomal enzymes are secreted to digest the bone

 Resorbs the organic part of bone

Histogenesis

Two types of bone development.

- intramembranous ossification

- endochondral ossification

In both these types of bone development temporary primary bone is deposited which is soon replaced by secondary bone. Primary bone has more osteocytes and the mineral content is lower.

Initially, four clefts exist; however, only one gives rise to a definite structure in adults.