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.

The Palate

• The palate forms the arched roof of the mouth and the floor of the nasal cavities.
• The palate consists of two regions: the anterior 2/3 or bony part, called the hard palate, and the mobile posterior 1/3 or fibromuscular part, known as the soft palate.

• 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 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.

The Auditory Tube

• This is a funnel-shaped tube connecting the nasopharynx to the tympanic cavity.

• Its wide end is towards the nasopharynx, where it opens posterior to the inferior meatus of the nasal cavity.
• The auditory tube is 3.5 to 4 cm long; its posterior 1/3 is bony and the other 2/3 is cartilaginous.
• It bony part lies in a groove on the inferior aspect of the base of the skull, between the petrous part of the temporal bone and the greater wing of the sphenoid bone.

• The function of the auditory tube is to equalise pressure of the middle ear with atmospheric pressure.