Nerves of the Palate

• The sensory nerves of the palate, which are branches of the pterygopalatine ganglion, are the greater and lesser palatine nerves.
• They accompany the arteries through the greater and lesser palatine foramina, respectively.

• The greater palatine nerve supplies the gingivae, mucous membrane, and glands of the hard palate.

• The lesser palatine nerve supplies the soft palate.

• Another branch of the pterygopalatine ganglion, the nasopalatine nerve, emerges from the incisive foramen and supplies the mucous membrane of the anterior part of the hard palate.

•  Provides a rigid support system
• Protects delicate structures (e. g., the protection provided by the bones of the vertebral column to the spinal cord)
• Bones supply calcium to the blood; are involved In the formation of blood cells (hemopoiesis)
• Bones serve as the basis of attachment of muscles; form levers in the joint areas, aIlowing movement

Eye 

At week 4, two depressions are evident on each of the forebrain hemispheres.  As the anterior neural fold closes, the optic pits elongate to form the optic vesicles.  The optic vesicles remain connected to the forebrain by optic stalks. 
The invagination of the optic vesicles forms a bilayered optic cup.  The bilayered cup becomes the dual layered retina (neural and pigmented layer)
Surface ectoderm forms the lens placode, which invaginates with the optic cup.
The optic stalk is deficient ventrally to contain choroids fissure to allow blood vessels into the eye (hyaloid artery).  The artery feeds the growing lens, but will its distal portion will eventually degenerate such that the adult lens receives no hyaloid vasculature.
At the 7th week, the choroids fissure closes and walls fuse as the retinal nerve get bigger.
The anterior rim of the optic vesicles forms the retina and iris.  The iris is an outgrowth of the distal edge of the retina.
Optic vesicles induces/maintains the development of the lens vesicle, which forms the definitive lens.  Following separation of the lens vesicle from the surface ectoderm, the cornea develops in the anterior 1/5th of the eye.
The lens and retina are surrounded by mesenchyme which forms a tough connective tissue, the sclera, that is continuous with the dura mater around the optic nerve.  
Iridopupillary membrane forms to separate the anterior and posterior chambers of the eye.  The membrane breaks down to allow for the pupil
Mesenchyme surrounding the forming eye forms musculature (ciliary muscles and pupillary muscles – from somitomeres 1 and 2; innervated by CN III), supportive connective tissue elements and vasculature.

Eyelids

Formed by an outgrowth of ectoderm that is fused at its midline in the 2nd trimester, but later reopen.

• The tongue is divided into halves by a medial fibrous lingual septum that lies deep to the medial groove.
• In each half of the tongue there are four extrinsic and four intrinsic muscles.

• The lingual muscles are all supplied by the hypoglossal nerve (CN XII).
• The only exception is palatoglossus, which is supplied by the pharyngeal branch of the vagus nerve, via the pharyngeal plexus.

•     Part of the axial skeleton; strong, flexible rod
      Supports the head
      Gives base to the ribs
      Encloses the spinal cord
      
  o    Vertebrae
      Consists of 34 bones composing the spinal column
  •    Cervical-7 bones
  •    Thoracic-12 bones
  •    Lumbar-5 bones
  •    Sacral- 5 bones.
  •    Coccygeal-4 to 5 bones

      In the adult the vertebrae of the sacral and coccygeal regions are united into two bones, the sacrum and me coccyx
      
  o    Curvatures-from a lateraI view there are four curves, alternately convex and concave ventrally
      Two convex curves are the cervical and lumbar
      Two concave curves are the thoracic and sacral

  o    Vertebra morphology

      Each vertebra differs in size and shape hut has similar components
      Body-central mass of bone
  •    Weight bearing
  •    Fonns anterior part of the vertebra
  •    Encloses the vertebral foramen
      Pedicles of the arch-two thick columns that extend backward from the body to meet with the laminae of the neural arch 

•     Process (7)
  •    One spinous, two transverse, two superior articular, and two inferior articular
  o    Spinous process extends backward from the point of the union of thetwo laminae
  o    Transverse processes project laterally at either side from the junction of the lamina and the pedicle
  o    Articular processes arise near the junction of the pedicle and the lamina- superior processes project upward:inferior processes project downward
  •    Surfaces of the processes are smooth

  o    Inferior articular processes of the vertebra fit into the superior articular processes below
  o    Form true joints, but the contacts established serve to restrict movement

  Distinguishing features

  Cervical region- triangular shape

  •    All have foramina in the transverse process upper six transmit the vertebral artery
  •    Spinous processes are short
      o    C3 to C5 are bifurcated
      o    C7 is long-prominence felt at the back of the neck
  •    Have small bodies (except for C1 vertebra)
  •    C1 vertebra (atlas)
  o    No body
  o    Anterior and posterior arch and two lateral masses
  o    Superiorarticular processes articulate with the condyles of the occipital bone
  •    C2 vertebra (axis)-process on the upper surface of the body (dens) forms a pivot about which the axis rotates

  Thoracic region

  •    Presence of facets for articulation with the ribs (distinguishing feature)
  •    Processes are larger and heavier than those of the cervical region
  •    Spinous process is directed downward at a sharp angle
  •    Circular vertebral foramen

   Lumbar region
   
  •    Large and heavy bodies
  •    Four transverse lines separate the bodies of the vertebrae on the pelvic surface
  •    Triangular shape-fitted between the  halves of the pelvis
  •    Four pairs of dorsal sacral foramina communicate with four pairs of pelvic sacral foramina

  Sacral vertebrae 
  •    Five (sometimes six) vertebrae are fused in the adult to form the sacrum
  •    The sacrum articulates above with L5, laterally with the hip bones, and inferiorly with the coccyx.
  •    It has a roughly triangular appearance with a pelvic and dorsal surface, a lateral mass on each side, and a base and apex.
  •    An anesthetic for the spinal nerves may be injected extradurally through the sacral hiatus (caudal analgesia)
  •    The sacral canal (which contains the dura, cauda equina, and filum terminale) extends from the base to the sacral hiatus. 
  •    The apex of the sacrum may be fused with the coccyx.

  
  Coccygeal vertebrae

  •    Four to five modular pieces fused together
  •    Triangular shape with the base above and the apex below

  F Defects

  •    Lordosis-exaggerated lumbar concavity
  •    Scoliosis-lateral curvature of any region
  •    Kyphosis-exaggerated convexity in the thoracic region

The External Ear

• The auricle (L. auris, ear) is the visible, shell-like part of the external ear.
• It consists of a single elastic cartilage that is covered on both surfaces with thin, hairy skin.
• The external ear contains hairs, sweat glands, and sebaceous glands.
• The cartilage is irregularly ridged and hollowed, which gives the auricle its shell-like form.
• It also shapes the orifice of the external acoustic meatus.

The Ear Lobule

• The ear lobule (earlobe) consists of fibrous tissue, fat and blood vessels that are covered with skin.
• The arteries are derived mainly from the posterior auricular artery and the superficial temporal artery.
• The skin of the auricle is supplied by the great auricular and auriculotemporal nerves.

• The great auricular nerve supplies the superior surface and the lateral surface inferior to the external acoustic meatus with nerve fibres from C2.
• The auriculotemporal nerve supplies the skin of the auricle superior to the external acoustic meatus.

The External Acoustic Meatus

• This passage extends from the concha (L. shell) of the auricle to the tympanic membrane (L. tympanum, tambourine). It is about 2.5 cm long in adults.
• The lateral 1/3 of the S-shaped canal is cartilaginous, whereas its medial 2/3 is bony.

• The lateral third of the meatus is lined with the skin of the auricle and contains hair follicles, sebaceous glands, and ceruminous glands.
• The latter glands produce cerumen (L. cera, wax).

• The medial two-thirds of the meatus is lined with very thin skin that is continuous with the external layer of the tympanic membrane.

• The lateral end of the meatus is the widest part. It has the diameter about that of a pencil.
• The meatus becomes narrow at its medial end, about 4 mm from the tympanic membrane.
• The constricted bony part is called the isthmus.

• Innervation of the external acoustic meatus is derived from three cranial nerves:

1. The auricular branch of the auriculotemporal nerve (derived from the mandibular, CN V³).
2. The facial nerve (CN VII) by the branches from the tympanic plexus.
3. The auricular branch of the vagus nerve (CN X).

The Tympanic Membrane

• This is a thin, semi-transparent, oval membrane at the medial end of the external acoustic meatus.
• It forms a partition between the external and middle ears.
• The tympanic membrane is a thin fibrous membrane, that is covered with very thin skin externally and mucous membrane internally.

• The tympanic membrane shows a concavity toward the meatus with a central depression, the umbo, which is formed by the end of the handle of the malleus.
• From the umbo, a bright area referred to as the cone of light, radiates anteroinferiorly.

• The external surface of the tympanic membrane is supplied by the auriculotemporal nerve.
• Some innervation is supplied by a small auricular branch of the vagus nerve (CN X); this nerve may also contain some glossopharyngeal and facial nerve fibres.