Ethmoid and Sphenoid Bone

Ethmoid Bone

Located deep within skull, posterior to facial skeleton

Forms part of: lateral walls of nasal cavity, medial walls of ocular orbit, floor of cranium, and nasal septum

Parts of the Ethmoid

1. Horizontal or Cribriform Plate

2. Lateral Labyrinths

3. Perpendicular Plate

Cribriform Plate

Horizontal portion of the bone

Spongy, has foramen that olfactory nerve passes through

Fits into the Ethmoid notch of the frontal bone to form part of the floor of the cranium

Has crista galli

Crista Galli

An attachment for the meninges of the brain, extending superiorly

Lateral Labyrinths

Form part of the orbits of the eye

Form part of the lateral wall of nasal cavity

Contain ethmoid sinuses

Have medial and superior nasal concha on each side

Ethmoid Sinuses

Most complex of the paranasal sinuses

Perpendicular Plate

Extends inferiority from center of horizontal plate

Forms part of the nasal septum, the division between the nostrils

Nasal Septum

Divides the nasal cavity into two spaces

Extends from nostrils to nasopharynx

Composed of septal cartilage and bone posteriorly

Sphenoid Bone

Articulates with all other cranial bones, and three facial bones

Forms part of the lateral cranial wall, ocular orbit, oropharynx, nasopharynx

Parts of the Sphenoid

1. Body

2. Greater Wings

3. Lesser Wings

4. Pterygoid Processes

Body

Sphenoid sinuses

Articulates with basilar portion occipital bone

On superior aspect has sella turcica, which houses pituitary gland

Greater Wings

Forms part of lateral cranial wall

Forms posterior portion of orbit of eye

Contributes to cranial floor

Located immediately anterior to petrous portion of temporal bone

Lesser Wings

Contributes to floor of cranial cavity, immediately posterior to horizontal portion of frontal bone

Contributes to the posterior roof of the orbit of the eyes

Pterygoid Processes

Left and right processes that descend from the place where the greater wings meet the body

Each process is divided into a medial and lateral plate

Hamulus

A hook-like projection at the end of the medial plate