The Temporomandibular Joint

• This articulation is a modified hinge type of synovial joint.
• The articular surfaces are: (1) the head or condyle of the mandible inferiorly and (2) the articular tubercle and the mandibular fossa of the squamous part of the temporal bone.

• An oval fibrocartilaginous articular disc divides the joint cavity into superior and inferior compartments. The disc is fused to the articular capsule surrounding the joint.

• The articular disc is more firmly bound to the mandible than to the temporal bone.

• Thus, when the head of the mandible slides anterior on the articular tubercle as the mouth is opened, the articular disc slides anteriorly against the posterior surface of the articular tubercle

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.

The Orbital Vessels

• The orbital contents are supplied chiefly by the ophthalmic artery.
• The infraorbital artery, the continuation of the maxillary, also contributes blood to this region.
• Venous drainage is through the superior orbital fissure to enter the cavernous sinus.

The Ophthalmic Artery

• This artery arises from the internal carotid artery as it emerges from the cavernous sinus.
• It passes through the optic foramen within the dural sheath of the optic nerve and runs anteriorly, close to the superomedial wall of the orbit.

The Central Artery of the Retina

• This is the one of the smallest but most important branches of the ophthalmic artery.
• It arises inferior to the optic nerve until it approaches the eyeball.
• It then pierces the optic nerve and runs within it to emerge through the optic disc.
• The central artery of the retina spreads over the internal surface of the retina and supplies it.

The Ophthalmic Veins

The Superior Ophthalmic Vein

• The superior ophthalmic vein anastomoses with the facial vein.
• It has no valves and blood can flow in either direction.
• It crosses superior to the optic nerve, passes through the superior orbital fissure and ends in the cavernous sinus.

The Inferior Ophthalmic Vein

• This begins as a plexus on the floor of the orbit.
• It communicates with the inferior orbital fissure with the pterygoid plexus, crosses inferior to the optic nerve, and ends in either the superior ophthalmic vein or the cavernous sinus.

-> This bone forms much of the base and posterior aspect of the skull.
-> It has a large opening called the foramen magnum, through which the cranial cavity communicates with the vertebral canal.
-> It is also where the spinal cord becomes continuous with the medulla (oblongata) of the brain stem.
-> The occipital bone is saucer-shaped and can be divided into four parts: a squamous part (squama), a basilar part (basioccipital part), and two lateral parts (condylar parts).
-> These four parts develop separately around the foramen magnum and unite at about the age of 6 years to form one bone.
-> On the inferior surfaces of the lateral parts of the occipital bone are occipital condyles, where the skull articulates with C1 vertebra (the atlas) at the atlanto-occipital joints.
-> The internal aspect of the squamous part of the occipital bone is divided into four fossae: the superior two for the occipital poles of the cerebral hemispheres, and the inferior two, called cerebellar fossae, for the cerebellar hemispheres.

• Cartilage model is covered with perichondrium that is converted to periosteum

• Diaphysis-central shaft
• Epiphysis-located at either end of the diaphysis
• Growth in length of the bone is provided by the emetaphyseal plate located between the epiphyseal cartilage and the diaphysis

• Blood capillaries and the mesenchymal cells infiltrate the spaces left by the destroyed chondrocytes

• Osteoblasts are derived from the undifferentiated cells; form an osseous matrix in the cartilage
• Bone appears at the site where there was cartilage

      Microscopic structure

• Compact bone is found on the exterior of all bones; canceIlous bone is found in the interior
• Surface of compact bone is covered by periosteum that is attached by Sharpey's fibers
• Blood vessels enter the periosteum via Volkmann's canals and then enter the haversian canals that are formed by the canaliculi and lacunae

•  

• Marrow
  • FiIls spaces of spongy bone
  • Contains blood vessels and blood ceIls in various stages of development
  • Types
• Red bone marrow
  • Formation of red blood ceIls (RBCs) and some white blood cells (WBCs) in this location
  • Predominate type of marrow in newborn
  • Found in spongy bone of adults (sternum, ribs, vertebrae, and proximal epiphyses of long bones)
•  Yellow bone marrow
  • Fatty marrow
  • Generally replaces red bone marrow in the adult, except in areas mentioned above
•  
• Ossification is completed as the proximal epiphysis joins with the diaphysis between the twentieth and twenty-fifth year

• 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