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.

• 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

The skull, the skeleton of the head, is the most complex bony structure in the body because it:

1. Encloses the brain, which is irregular in shape;
2. Houses the organs of special senses for seeing, hearing, tasting, and smelling; and
3. Surrounds the openings in to the digestive and respiratory tracts.

• In the anatomical position, the skull is oriented so that the inferior margin of the orbit (eye socket) and the superior margin of the external acoustic meatus (auditory canal) are horizontal. This is called the orbitomenial plane (Frankfort plane).

• The term cranium (L. skull) is sometimes used when referring to the skull without the mandible (lower jaw), but the cranium is often used when referring to the part of the skull containing the brain.
• The superior part is the box-like structure called the calvaria (cranial vault, brain case); the remainder of the cranium, including the maxilla (upper jaw), orbits (eyeball sockets) and nasal cavities, forms the facial skeleton.
• The term skullcap (calotte) refers to the superior part of the calvaria, which is removed during autopsies and dissections. The inferior aspect of the cranium is called the cranial base.

The Middle Ear

• This part of the ear is in a narrow cavity in the petrous part of the temporal bone.
• It contains air, three auditory ossicles, a nerve and two small muscles.
• The middle ear is separated from the external acoustic meatus by the tympanic membrane.

• This cavity includes the tympanic cavity proper, the space directly internal to the tympanic membrane, and the epitympanic recess, the space superior to it.

• The middle ear is connected anteriorly with the nasopharynx by the auditory tube.
• Posterosuperiorly, the tympanic cavity connects with the mastoid cells through the aditus ad antrum (mastoid antrum).
• The tympanic cavity is lined with mucous membrane that is continuous with the mucous membrane of the auditory tube, mastoid cells, and aditus ad antrum.

Contents of the Tympanic Cavity or Middle Ear

• This cavity contains the auditory ossicles (malleus, incus and stapes); the stapedius and tensor tympani muscles; the chorda tympani nerve (a branch of the facial nerve, CN VII); and the tympanic plexus of nerves.

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.