• BONES OF THE CRANIUM   Occipital (1) Frontal    (1) Sphenoid (1) Ethmoid  (1) Parietal    (2) Temporal  (2)

  BONES OF THE FACE   Mandible (1) Vomer     (1) Maxillae  (2) Zygomae  (2) Lacrimal   (2) Nasal        (2) Inferior nasal conchae (2) Palatine     (2)

   

• Articulations

  Classified according to their structure, composition,and movability
  •    Fibrous joints-surfaces of bones almost in direct contact with limited movement
      o    Syndesmosis-two bones united by interosseous ligaments
      o    Sutures-serrated margins of bones united by a thin layer of fibrous tissue
      o    Gomphosis-insertion of a cone-shaped process into a socket

  •    Cartilaginous joints-no joint cavity and contiguous bones united by cartilage
      o    Synchondrosis-ends of two bones approximated by hyaline cartilage
      o    Symphyses-approximating bone surfaces connected by fibrocartilage

  •    Synovial joints-approximating bone surfaces covered with cartilage; may be separated by a disk; attached by ligaments 
      o    Hinge-permits motion in one plane only
      o    Pivot-permits rotary movement in which a ring rotates around a central axis
      o    Saddle-opposing surfaces are convexconcave. allowing great freedom of motion
      o    Ball and socket - capable of movement in an infinite number of axes; rounded head of one bone moves in a cuplike cavity of the approximating bone

  Bursae
  •    Sacs filled with synovial fluid that are present where tendons rub against bone or where skjn rubs across bone
  •    Some bursae communicate with a joint cavity 
  •    Prominent bursae found at the elbow. hip, and knee'

  Movements
  •    Gliding
      o    Simplest kind of motion in a joint
      o    Movement on a joint that does not involve any angular or rotary motions
  •    Flexion-decreases the angle formed by the union of two bones
  •    Extension-increases the angle formed by the union of two bones
  •    Abduction-occurs by moving part of the appendicular skeleton away from the median plane of the body
  •    Adduction-occurs by moving part of the appendicular skeleton toward the median plane of the body
  •    Circumduction
      o    Occurs in ball-and-socket joints
      o    Circumscribes the conic space of one bone by the other bone
  •    Rotation-turning on an axis without being displaced from that axis
   

The Oropharynx

• The oral part of the pharynx has a digestive function.
• It is continuous with the oral cavity through the oropharyngeal isthmus.
• The oropharynx is bounded by the soft palate superiorly, the base of the tongue inferiorly, and the palatoglossal and palatopharyngeal arches laterally.

• It extends from the soft palate to the superior border of the epiglottis.

The Palatine Tonsils

• These are usually referred to as "the tonsils".
• They are collections of lymphoid tissue the lie on each side of the oropharynx in the triangular interval between the palatine arches.

• The palatine tonsils vary in size from person to person.
• In children, the palatine tonsils tend to be large, whereas in older persons they are usual small and inconspicuous.
• The visible part of the tonsil is no guide to its actual size because much of it may be hidden by the tongue and buried in the soft palate.

• This is the posterior curtain-like part, and has no bony support. It does, however, contain a membranous aponeurosis.
• The soft palate, or velum palatinum (L. velum, veil), is a movable, fibromuscular fold that is attached to the posterior edge of the hard palate.
• It extends posteroinferiorly to a curved free margin from which hangs a conical process, the uvula (L. uva, grape).

• The soft palate separates the nasopharynx superiorly and the oropharynx inferiorly.

• During swallowing the soft palate moves posteriorly against the wall of the pharynx, preventing the regurgitation of food into the nasal cavity.

• Laterally, the soft palate is continuous with the wall of the pharynx and is joined to the tongue and pharynx by the palatoglossal and palatopharyngeal folds.

• The soft palate is strengthened by the palatine aponeurosis, formed by the expanded tendon of the tensor veli palatini muscle.
• This aponeurosis attaches to the posterior margin of the hard palate.

Tongue 
Appears at 4th week.
Musculature derived from mesoderm of occipital somites.  Precursor muscles cells migrate to region of tongue and are innervated by general sensory efferent fibers of CN XII.
Mucosa derived from anterior endoderm lining arches 1-4; accordingly, innervation depends on arch derivation:
              Mucosa of anterior 2/3 of tongue comes from the first arch -> CN V
              Mucosa of posterior 1/3 of tongue comes from third and forth arch -> CN IX, X
Special taste of anterior 2/3 of tongue comes from CN VII.
Special taste of posterior 1/3 of tongue comes from CN X.
Tongue freed from floor of mouth by extensive degeneration of underlying tissue.  Midline frenulum continues to anchor tongue to floor of mouth.

Thyroid Gland

Develops as in growth of mucosal epithelium located in the midline of the tongue (at foramen cecum).  It descends along front of pharyngeal gut, but remains connected to tongue by thyrooglossal duct, which is obliterated later in development.  Thyroid gland descends to a point just caudal to laryngeal cartilages. 

Facial structures (general)

a) medial nasal prominence forms midline of nose, philtrum and primary palate
b) lateral nasal prominence forms alae of nose
c) maxillary prominence forms cheek region and lateral lip
d) clefts can form at inter-prominence fusion lines

Nose

At the time of anterior neural tube closure, mesenchyme around forebrain, frontonasal prominence (FNP), has smooth rounded extended contour.  Nasal placodes (thickening of surface ectoderm to become peripheral neural tissue) develop on frontolateral aspects of FNP.  Mesenchyme swells around nasal placode producing a medial and lateral nasal prominence (nasomedial and nasolateral processes).  These nasal prominences form the nose.

Mouth 

Stomadeum (primitive oral cavity) forms between frontonasal prominence and first pharyngeal arch.  The first pharyngeal arch forms the dorsal maxillary prominence and ventral mandibular prominence.  The maxillary prominence will merge with medial nasal prominences, pushing them closer to cause fusion.  Fused medial nasal prominences will form midline of nose and midline of upper lip (philtrum) and primary palate (first 4 teeth).

Nasolacrimal structures

Maxillary and lateral nasal prominences are separated by deep furrow, the nasolacrimal groove.  Ectoderm in floor of groove forms epithelial cord, which detaches from overlying ectoderm.  The epithelial cord canalizes to form the nasolacrimal duct.  The upper end of the duct widens to form the lacrimal sac.  After detachment of the cord, the maxillary and lateral nasal prominences merge with each other, resulting in the formation of a nasolacrimal duct that runs from the medial corner of the eye to the inferior meatus of the nasal cavity.  
The maxillary prominences enlarge to form the cheeks and maxillae.
The lateral nasal prominences form the alae of the nose.

Secondary (hard) palate

Main part of definitive palate formed by two palatine shelves derived from intraoral bilateral extensions of the maxillary prominences.  These appear at the 6th week.  They are directed obliquely downward on each side of the tongue; they move down when mandible gets bigger.  
At the seventh week, they ascend to attain a horizontal position, then fuse to form the secondary palate.  At the time the palatine shelves fuse, the nasal septum (an outgrowth of median tissue of the frontonasal prominence) grows down and joins the cephalic aspect of the newly formed palate
Anteriorly, shelves fuse with triangular primary palate.  The incisive foramen marks the midline between the primary and secondary palate.

External Ear

The auricle is derived from 6 auricular hillocks (mesenchymal proliferations) along the dorsal aspect of arches 1 (top of ear) and 2 (bottom of ear).  These fuse to form the definitive auricle.  At the mandible grows, the ear is pushed upward and backward from its initial horizontal position on the neck.
The EAM is derived from the 1st pharyngeal arch.  
The eardrum (tympanic membrane) is composed of 3 layers of cells: 1) ectodermal epithelial lining of bottom of EAM; 2) endodermal epithelium lining of tympanic cavity; 3) intermediate layer of connective tissue.
The eardrum is composed of multiple cell layers because it represents the first pharyngeal membrane, and thus lies at the junction of the first pharyngeal pouch and cleft.

Middle Ear

The middle ear consists of an auditory tube (from the 1st pharyngeal pouch, along with tympanic cavity) and the ossicles (from pharyngeal arches 1 and 2 cartilage).  
The first arch cartilage forms the malleus and incus.  The tensor tympani (muscle of the malleus) is derived from the fourth somitomere (associated with the first arch) and is therefore innervated by CN V.
The second arch cartilage forms the stapes.  The stapedius (muscles of the stapes) is derived from the sixth somitomere (associated with the second arch) and is therefore innervated by CN VII.
The ossicles are initially embedded in mesenchyme, but in the 8th month, the mesenchyme degenerates and an endodermal epithelial lining of the tympanic cavity envelops the ossicles and connects them to the wall of the cavity in a mesentery-like fashion.

Inner Ear

The inner ear is derived thickening of surface ectoderm on both sides of the hindbrain (otic placodes).  The placodes invaginate to form otic vesicles (otocytes).  The vesicles then divide into ventral and dorsal components.
The ventral component forms the saccule and cochlear duct.
The dorsal component forms the utricle and semicircular canals and endolymphatic duct.

Cochlear Duct

Derived from an outgrowth of the saccule during the 6th week.  The outgrowth penetrates the surrounding mesenchyme in a spiral fashion.  The surrounding mesenchyme forms the cartilage and undergoes vacuolization.
The scala vestibule and scale tympani form and surround the cochlear duct.  They are filled with periplymp to receive mechanical vibrations of ossicles. The mechanical stimuli activates sensory (ciliary) cells in the cochlear duct.  

Semicircular canals

The utricle is initially three flattened outpocketings, which lose the central core.  From this three semicircular canals are forms, each at 90 degree angles from one another.  Sensory cells arise in the ampulla at one end of each canal, in the utricle and saccule. 

The Orbital Margin

• The frontal, maxillary and zygomatic bones contribute equally to the formation of the orbital margin.

• The supraorbital margin is composed entirely of the frontal bone.
• At the junction of its medial and middle thirds is the supraorbital foramen (sometimes a notch), which transmits the supraorbital nerves and vessels.

• The lateral orbital margin is formed almost entirely of the frontal process of the zygomatic bone.

• The infraorbital margin is formed by the zygomatic bone laterally and the maxilla medially.

• The medial orbital margin is formed superiorly by the frontal bone and inferiorly by the lacrimal crest of the frontal process of the maxilla.
• This margin is distinct in its inferior half only.