-> This is a wedge-shaped bone (G. sphen, wedge) is located anteriorly to the temporal bones.
-> It is a key bone in the cranium because it articulates with eight bones (frontal, parietal, temporal, occipital, vomer, zygomatic, palatine, and ethmoid).
-> It main parts are the body and the greater and lesser wings, which spread laterally from the body.
-> The superior surface of its body is shaped like a Turkish saddle (L. sella, a saddle); hence its name sella turcica.
-> It forms the hypophyseal fossa which contains the hypophysis cerebri or pituitary gland.
-> The sella turcica is bounded posteriorly by the dorsum sellae, a square plate of bone that projects superiorly and has a posterior clinoid process on each side.
-> Inside the body of the sphenoid bone, there are right and left sphenoid sinuses. The floor of the sella turcica forms the roof of these paranasal sinuses.
-> Studies of the sella turcica and hypophyseal fossa in radiographs or by other imaging techniques are important because they may reflect pathological changes such as a pituitary tumour or an aneurysm of the internal carotid artery. Decalcification of the dorsum sellae is one of the signs of a generalised increase in intracranial pressure.

The Sublingual Glands

• These are the smallest of the three paired salivary glands and the most deeply situated.
• They are almond-shaped and lie in the floor of the mouth between the mandible and the genioglossus muscle.
• The paired glands unite to form a horseshoe-shaped glandular mass around the lingual frenulum.

• Numerous small ducts (10 to 12) open into the floor of the mouth.
• Sometimes one of the ducts opens into the submandibular duct.

• The nerves the accompany the submandibular and sublingual glands are derived from the lingual and chorda tympani nerves and from the sympathetic nerves.
• The parasympathetic secretomotor fibres are from the submandibular ganglion.

The Oral Cavity

• The oral cavity (mouth) consists of two parts: the vestibule and the mouth proper.

• The vestibule is the slit-like spaced between the cheeks and the lips and the teeth and gingivae.
• It is the entrance of the digestive tract and is also used for breathing.
• The vestibule communicates with the exterior through the orifice of the mouth.

• The oral cavity is bounded:
• Externally: by the cheeks and lips.
• Roof of oral cavity: formed by the palate.
• Posteriorly: the oral cavity communicates with the oropharynx.

The Ear

• The ear contains the vestibulocochlear organ and consists of three main parts: external, middle, and internal.
• It has two functions, balance and hearing.

• The tympanic membrane (eardrum) separates the external ear from the middle ear.
• The auditory tube joins the middle ear or tympanic cavity to the nasopharynx.

The Medial Pterygoid Muscle

• This is a thick, quadrilateral muscle that also has two heads or origin.
• It embraces the inferior head of the lateral pterygoid muscle.
• It is located deep to the ramus of the mandible.

• Origin: deep head—medial surface of lateral pterygoid plate and pyramidal process of palatine bone, superficial head—tuberosity of maxilla.
• Insertion: medial surface of ramus of mandible, inferior to mandibular foramen.
• Innervation: mandibular nerve via medial pterygoid nerve.

• It helps to elevate the mandible and closes the jaws.
• Acting together, they help to protrude the mandible.
• Acting alone, it protrudes the side of the jaw.
• Acting alternately, they produce a grinding motion.

Muscles Moving the Auditory Ossicles

The Tensor Tympani Muscle

• This muscle is about 2 cm long.

• Origin: superior surface of the cartilaginous part of the auditory tube, the greater wing of the sphenoid bone, and the petrous part of the temporal bone.
• Insertion: handle of the malleus.
• Innervation: mandibular nerve (CN V³) through the nerve to medial pterygoid.

• The tensor tympani muscle pulls the handle of the malleus medially, tensing the tympanic membrane, and reducing the amplitude of its oscillations.
• This tends to prevent damage to the internal ear when one is exposed to load sounds.

The Stapedius Muscle

• This tiny muscle is in the pyramidal eminence or the pyramid.

• Origin: pyramidal eminence on the posterior wall of the tympanic cavity. Its tendon enters the tympanic cavity by traversing a pinpoint foramen in the apex of the pyramid.
• Insertion: neck of the stapes.
• Innervation: nerve to the stapedius muscle, which arises from the facial nerve (CN VII).

• The stapedius muscle pulls the stapes posteriorly and tilts its base in the fenestra vestibuli or oval window, thereby tightening the anular ligament and reducing the oscillatory range.
• It also prevents excessive movement of the stapes.