•     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

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 Hard Palate

• The anterior bony part of the palate is formed by the palatine process of the maxillae and the horizontal plates of the palatine bones.

• Anteriorly and laterally, the hard palate is bounded by the alveolar processes and the gingivae.
• Posteriorly, the hard palate is continuous with the soft palate.

• The incisive foramen is the mouth of the incisive canal.
• This foramen is located posterior to the maxillary central incisor teeth.
• This foramen is the common opening for the right and left incisive canals.
• The incisive canal and foramen transmit the nasopalatine nerve and the terminal branches of the sphenopalatine artery.

• Medial to the third molar tooth, the greater palatine foramen pierces the lateral border of the bony palate.
• The greater palatine vessels and nerve emerge from this foramen and run anteriorly into two grooves on the palate.

• The lesser palatine foramen transmits the lesser palatine nerve and vessels.
• This runs to the soft palate and adjacent structures.

Muscles of the Tongue

• 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.

Extrinsic Muscles of the Tongue

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 Palatopharyngeus Muscle

• Superior attachment: hard palate and palatine aponeurosis.
• Inferior attachment: lateral wall of pharynx.
• Innervation: cranial part of accessory nerve (CN XI) through the pharyngeal branch of vagus (CN X) via the pharyngeal plexus.

• This thin, flat muscle is covered with mucous membrane to form the palatopharyngeal arch.
• It passes posteroinferiorly in this arch.

• This muscle tenses the soft palate and pulls the walls of the pharynx superiorly, anteriorly and medially during swallowing. 

Intrinsic Muscles of the Tongue

The Superior Longitudinal Muscle of the Tongue

• The muscle forms a thin layer deep to the mucous membrane on the dorsum of the tongue, running from its tip to its root.
• It arises from the submucosal fibrous layer and the lingual septum and inserts mainly into the mucous membrane.

• This muscle curls the tip and sides of the tongue superiorly, making the dorsum of the tongue concave.

The Inferior Longitudinal Muscle of the Tongue

• This muscle consists of a narrow band close to the inferior surface of the tongue.
• It extends from the tip to the root of the tongue.
• Some of its fibres attach to the hyoid bone.

• This muscle curls the tip of the tongue inferiorly, making the dorsum of the tongue convex.

The Transverse Muscle of the Tongue

• This muscle lies deep to the superior longitudinal muscle.
• It arises from the fibrous lingual septum and runs lateral to its right and left margins.
• Its fibres are inserted into the submucosal fibrous tissue.

• The transverse muscle narrows and increases the height of the tongue.

The Vertical Muscle of the Tongue

• This muscle runs inferolaterally from the dorsum of the tongue.
• It flattens and broadens the tongue.
• Acting with the transverse muscle, it increases the length of the tongue.

Muscles Around the Nose

The Nasalis Muscle

• This muscle consists of a transverse (compressor naris) and alar (dilator naris) parts.
• It is supplied by the buccal branch of the facial nerve.

• 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)