Structure of the Nasal Septum

• This part bony, part cartilaginous septum divides the chamber of the nose into two narrow nasal cavities.
• The bony part of the septum is usually located in the median plane until age 7; thereafter, it often deviates to one side, usually the right.

• The nasal septum has three main components: (1) the perpendicular plate of the ethmoid bone; (2) the vomer, and (3) the septal cartilage.

• The perpendicular plate, which forms the superior part of the septum, is very thin and descends from the cribiform plate of the ethmoid bone.
• The vomer, which forms the posteroinferior part of the septum, is a thin, flat bone. It articulates with the sphenoid, maxilla and palatine bones.

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 Skeleton of the Nose

• The immovable bridge of the nose, the superior bony part of the nose, consists of the nasal bones, the frontal processes of the maxillae, and the nasal part of the frontal bones.

• The movable cartilaginous part consists of five main cartilages and a few smaller ones.
• The U-shaped alar nasal cartilages are free and movable.
• They dilate and constrict the external nares when the muscles acting on the external nose contract.

The Nasal Cavities

• The nasal cavities are entered through the anterior nares or nostrils.
• They open into the nasopharynx through the choanae.

The Roof and Floor of the Nasal Cavity

• The roof is curved and narrow, except at the posterior end.

• The floor is wider than the roof.
• It is formed from the palatine process of the maxilla and the horizontal plate of the palatine bone.

The Walls of the Nasal Cavity

• The medial wall is formed by the nasal septum; it is usually smooth.

• The lateral wall is uneven owing to the three longitudinal, scroll-shaped elevations, called the conchae (L. shells) or turbinates (L. shaped like a top).
• These elevations are called the superior, middle and inferior conchae according to their position.

• The superior and middle conchae are parts of the ethmoid bone, whereas the inferior conchae are separate bones.

• The inferior and middle conchae project medially and inferiorly, producing air passageways called the inferior and middle meatus (L. passage). Note: the plural of "meatus" is the same as the singular.
• The short superior conchae conceal the superior meatus.
• The space posterosuperior to the superior concha is called the sphenoethmoidal recess.

The Cheeks

• The cheeks (L. buccae) form the lateral wall of the vestibule of the oral cavity.
• They have essentially the same structure as the lips with which they are continuous.

• The principal muscular component of the cheeks is the buccinator muscle.
• Superficial to the fascia covering this muscle is the buccal fatpad that gives cheeks their rounded contour, especially in infants.

• The lips and cheeks act as a functional unit (e.g. during sucking, blowing, eating, etc.).
• They act as an oral sphincter in pushing food from the vestibule to the oral cavity proper.
• The tongue and buccinator muscle keep the food between the molar teeth during chewing.

Sensory Nerves of the Cheeks

• These are branches of the maxillary and mandibular nerves.
• They supply the skin of the cheeks and the mucous membrane lining the cheeks.

Nerves of the Palate

• The sensory nerves of the palate, which are branches of the pterygopalatine ganglion, are the greater and lesser palatine nerves.
• They accompany the arteries through the greater and lesser palatine foramina, respectively.

• The greater palatine nerve supplies the gingivae, mucous membrane, and glands of the hard palate.

• The lesser palatine nerve supplies the soft palate.

• Another branch of the pterygopalatine ganglion, the nasopalatine nerve, emerges from the incisive foramen and supplies the mucous membrane of the anterior part of the hard palate.

Vessels of the Palate

• The palate has a rich blood supply from branches of the maxillary artery.