Orbital part of frontal bone

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Orbital part of frontal bone
Frontal bone. Outer surface. (The Pars orbitalis is the bottom third.)
Frontal bone. Inner surface. (The Pars orbitalis is the bottom third.)
Latin	pars orbitalis ossis frontalis
Gray's	subject #33 137
Dorlands/Elsevier	p_07/12617384

The orbital or horizontal part of the frontal bone (pars orbitalis) consists of two thin triangular plates, the orbital plates, which form the vaults of the orbits, and are separated from one another by a median gap, the ethmoidal notch.

[edit] Surfaces

• The inferior surface of each orbital plate is smooth and concave, and presents, laterally, under cover of the zygomatic process, a shallow depression, the lacrimal fossa, for the lacrimal gland; near the nasal part is a depression, the fovea trochlearis, or occasionally a small trochlear spine, for the attachment of the cartilaginous pulley of the obliquus oculi superior.
• The superior surface is convex, and marked by depressions for the convolutions of the frontal lobes of the brain, and faint grooves for the meningeal branches of the ethmoidal vessels.
  • The ethmoidal notch separates the two orbital plates; it is quadrilateral, and filled, in the articulated skull, by the cribriform plate of the ethmoid.
    • The margins of the notch present several half-cells which, when united with corresponding half-cells on the upper surface of the ethmoid, complete the ethmoidal air cells.
  • Two grooves cross these edges transversely; they are converted into the anterior and posterior ethmoidal canals by the ethmoid, and open on the medial wall of the orbit.
    • The anterior canal transmits the nasociliary nerve and anterior ethmoidal vessels,
    • the posterior, the posterior ethmoidal nerve and vessels.

• In front of the ethmoidal notch, on either side of the frontal spine, are the openings of the frontal air sinuses.
  • These are two irregular cavities, which extend backward, upward, and lateralward for a variable distance between the two tables of the skull; they are separated from one another by a thin bony septum, which often deviates to one or other side, with the result that the sinuses are rarely symmetrical.
  • Absent at birth, they are usually fairly well-developed between the seventh and eighth years, but only reach their full size after puberty.
  • They vary in size in different persons, and are larger in men than in women.
  • They are lined by mucous membrane, and each communicates with the corresponding nasal cavity by means of a passage called the frontonasal duct.

[edit] Additional images

The seven bones which articulate to form the orbit.

Medial wall of left orbit.

[edit] External links

• SUNY Labs 29:st-0202 (orbital plate)
• Roche Lexicon - illustrated navigator, at Elsevier 34256.000-1

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained herein may be outdated. Please edit the article if this is the case, and feel free to remove this notice when it is no longer relevant.

v • d • e Bones of head and neck: the cranium of the skull Occipital Squama external (Inion/External occipital protuberance, Nuchal lines) - planes (Occipital, Nuchal) - internal (Cruciform eminence, Internal occipital protuberance, Sagittal sulcus, Internal occipital crest) Lateral parts Condyle (Condyloid fossa, Condylar canal) - Hypoglossal canal - jugular (Jugular process, Jugular tubercle) Basilar part Pharyngeal tubercle Other Foramen magnum Parietal Parietal eminence - Temporal line - Parietal foramen Frontal Squama Frontal suture - Frontal eminence - external (Superciliary arches, Glabella) - foramina (Supraorbital, Cecum) - Zygomatic process - internal (Sagittal sulcus, Frontal crest) Orbital part Ethmoidal notch - Lacrimal fossa - Trochlear fovea - Frontal sinus - Frontonasal duct Temporal Squama Articular tubercle - Suprameatal triangle - Mandibular fossa - Petrotympanic fissure - Zygomatic process Mastoid part Mastoid foramen - Mastoid process (Mastoid cells) - Mastoid notch - Occipital groove - Sigmoid sulcus - Mastoid antrum (Entrance) Petrous part Carotid canal - Facial canal (Hiatus) - Internal auditory meatus - Aqueduct of cochlea - Stylomastoid foramen fossae (Subarcuate fossa, Jugular fossa) - canaliculi (Inferior tympanic, Mastoid) - Styloid process - Petrosquamous suture (note: ossicles in petrous part, but not part of temporal bone) Tympanic part Suprameatal spine Sphenoid Surfaces Superior surface: Sella turcica (Dorsum sellae, Tuberculum sellae, Hypophysial fossa, Posterior clinoid processes) - Ethmoidal spine - Chiasmatic groove - Middle clinoid process - Petrosal process - Clivus Lateral surface: Carotid groove - Sphenoidal lingula Anterior surface: Sphenoidal sinuses Great wings foramina (Rotundum, Ovale, Vesalii, Spinosum) - Spine - Infratemporal crest - Sulcus for auditory tube Small wings Superior orbital fissure - Anterior clinoid process - Optic canal Pterygoid processes fossae (Pterygoid, Scaphoid) - pterygoid plates (Lateral, Medial) - Pterygoid canal - Hamulus Other Body - Sphenoidal conchae Ethmoid Plates Cribriform plate (Crista galli, Olfactory foramina) - Perpendicular plate Surfaces Lateral surface Orbital lamina - Uncinate process Medial surface Superior nasal concha - Superior meatus - Middle nasal concha - Middle meatus Labyrinth Ethmoid sinus - ethmoidal foramina (Posterior, Anterior)