The Paranasal Sinuses

• These sinuses are air-filled extensions of the respiratory part of the nasal cavity.
• They are in the following bones, frontal, ethmoid, sphenoid and the maxilla.

The Frontal Sinuses

• These are located between the outer and inner tables of the frontal bone, posterior to the superciliary arches.

The Ethmoidal Sinuses

• These comprise of several small cavities, called ethmoidal air cells, within the ethmoidal labyrinth (G. labyrinthos, a maze) of the lateral mass of the ethmoid bone.

The Sphenoidal Sinuses

• These occupy a variable amount in the body of the sphenoid bone and may extend into the wings.

The Maxillary Sinuses

• These are the largest pair of paranasal sinuses.
• They are pyramidal-shaped cavities that may occupy the entire bodies of the maxillae.

-> 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).

A. Anatomic position-erect body position with the arms at the sides and the palms  upward

B. Plane or section

1. Definition-imaginary flat surface formed by an extension through an axis

2. Median plane-a vertical plane. that divides a body into right and left halves

3. Sagittal plane

• Any plane parallel to the median plane
• Divides the body into right and left portions

4. Frontal plane

• Vertical plane that forms at right angles to the sagittal plane
• Divides the body into anterior and posterior sections
• Synonymous with the term coronal plane

5. Transverse plane

• Horizontal plane that forms at right angles to the sagittal and frontal planes
• Divides the body into upper and lower portions
• Synonymous with the term horizontal plane

C. Relative positions

1. Anterior

• Nearest the abdominal surface and the front of the body
• Synonymous with the term ventral
• In referring to hands and forearms, the terms palmar and Volar are used

2. Posterior

• Back of the body
• Synonymous with the term dorsal

3. Superior

• Upper or higher
• Synonymous with the term cranial (head)

4. Inferior

• Below or lower
• Synonymous with the term caudal (tail)
• In referring to the top of the foot and the sole of the foot. the terms dorsal and plantar are used respectively

5. Medial-near to the median plane

6. Lateral-farther away from the median plane

7. Proximal-near the source or attachment

8. Distal-away from the source or. attachment

9. Superficial-near the surface

10. Deep-away from the surface

11. Afferent-conducting toward a structure

12. Efferent-conducting away from a structure

• Skull 
  Cranium
  o    Superior portion formed by the frontal. parietal, and occipital bones
  o    Lateral portions formed by the temporal and sphenoid bones
  o    Cranial base formed by the temporal. sphenoid, and ethmoid bones
  o    Fontanels-soft spots in which ossification is incomplete at birth

  Frontal bone
  o    Forms the forehead
  o    Contains the frontal sinuses
  o    Forms the roof of the orbits
  o    Union with the parietal bones forms the coronal suture

  Parietal bones
  o    Union with the occipital bone forms the lambdoid suture
  o    Union with the temporal bone forms the squamous suture
  o    Union with the sphenoid bone forms the coronal suture

  Temporal bones
  o    Contains the external auditory meatus and middle and inner ear structures
  o    Squamous portion-above the meatus: zygomatic process-articulates with the zygoma
  o    to form the zygomatic arch 

  •    Petrous portion
  o    Contains organs of hearing and equilibrium 
  o    Prominent elevation on the floor of the cranium

  •    Mastoid portion
  o    Protuberance behind the ear

  o    Mastoid process
  •    Glenoid fossa-articulates with the condyle on the mandible
  •    Styloid process-anterior to the mastoid process; several neck muscles attach here
  •    Stylomastoid foramen-located between the styloid and mastoid processes; facial nerve emerges through this opening
  •    Jugular foramen-located between the petrous portion and the occipital bone: cranial nerves IX. X, and XI exit
   

• Ossification

• Intramembranous-found in the flat bones of the face
  • Mesenchymal cells cluster and form strands
  • Strands are cemented in a uniform network. Which is known as osteoid
  • Calcium salts are deposited; osteoid is converted to bone
  • Trabeculae are formed and make cancellous bone with open spaces known as marrow cavities
  • Periosteum forms on the inner and outer surfaces of the ossification centers
  • Surface bone becomes compact bone
• Endochondral-primary type of ossification In the human

Extrinsic Muscles of the Tongue (p. 746)

The Genioglossus Muscle

• This is a bulky, fan-shaped muscle that contributes to most of the bulk of the tongue.
• It arises from a short tendon from the genial tubercle (mental spine) of the mandible.
• It fans out as it enters the tongue inferiorly and its fibres attach to the entire dorsum of the tongue.
• Its most inferior fibres insert into the body of the hyoid bone.
• The genioglossus muscle depresses the tongue and its posterior part protrudes it.

The Hyoglossus Muscle

• This is a thin, quadrilateral muscle.
• It arises from the body and greater horn of the hyoid bone and passes superoanteriorly to insert into the side and inferior aspect of the tongue.
• It depresses the tongue, pulling its sides inferiorly; it also aids in retrusion of the tongue.

The Styloglossus Muscle

• This small, short muscle arises from the anterior border of the styloid process near its tip and from the stylohyoid ligament.
• It passes inferoanteriorly to insert into the side and inferior aspect of the tongue.
• The styloglossus retrudes the tongue and curls its sides to create a trough during swallowing.

The Palatoglossus Muscle 

• Superior attachment: palatine aponeurosis.
• Inferior attachment: side of tongue.
• Innervation: cranial part of accessory nerve (CN XI) through the pharyngeal branch of vagus (CN X) via the pharyngeal plexus.

• This muscle, covered by mucous membrane, forms the palatoglossal arch.

• The palatoglossus elevates the posterior part of the tongue and draws the soft palate inferiorly onto the tongue.