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You are watching: Which of the following bones is not part of the orbit?

StatPearls . Endowment Island (FL): StatPearls Publishing; 2021 Jan-.


Anatomy, Head and Neck, Orbit Bones

Caleb L. Shumway; Mahsaw Motlagh; Matthew Wade.

Author Information

The orbit is a pear shape, through the optic nerve at the stem, and also holds about 30 cc volume. The enntrance gate to the globe anteriorly is about 35 mm high and also 45 mm wide. The depth from orbit rim come the orbit apex procedures 40 to 45 mm in adults. The maximum broad is 1 cm behind the anterior orbit margin. Both race and also gender can impact the dimensions of the bony orbit. The orbital cavity contains the globe, nerves, vessels, lacrimal gland, extraocular muscles, tendons, and also the trochlea and fat and other connective tissue. Boost in the volume that the extraocular structures within the orbit can reason proptosis, i m sorry is protrusion that the world and/or displacement (deviation) of the globe from its regular position.

The orbital margin is the anterior opening of the globe and has a quadrilateral spine created by number of of the bones that make up the orbit. The roof that the orbit is developed by the orbit plate the the frontal bone and the lesser soup of the sphenoid.  The fossa of the lacrimal gland lies anterolaterally, behind the zygomatic process of the frontal bone.

Walls of the Orbit

The orbit roof is composed of two components of 2 bones, the orbital plate frontal bone and also the lesser soup of the sphenoid bone. The fossa the the lacrimal gland is in the orbit roof, and it lies anteriorly and laterally behind the zygomatic procedure of the frontal bone. The trochlear fossa is medial and around 4 mm native the orbit margin. This is where the pulley of the exceptional oblique is attached.

The medial orbital wall consists of 4 bones, the frontal procedure of the maxillary bone: the lacrimal bone, the orbit plate the the ethmoid bone, and the lesser soup of the sphenoid bone. The largest component of the medial wall surface is from the ethmoid bone. The frontal process of the lacrimal fossa and also the bony nasolacrimal canal are consistent and extend into the inferior meatus of the sleep cavity. The medial wall of the ethmoid bone is actually very thin and also is referred to as the lamina papyracea. 

The floor the the orbit is composed of three bones: the maxillary bone, the palatine bone, and also the orbital plate the the zygomatic bone. This component of the orbit is likewise the roof the the maxillary sinus. Over there is one infraorbital groove follow me the floor and it travels right into a canal anteriorly where it ultimately exits as the infraorbital foramen. This is the structure that lies below the orbital margin that the maxillary bone. Along the floor the the orbit is the beginning of the inferior oblique muscle. This is the only extraocular muscle that does no originate in ~ the apex that the orbit.

Lateral orbit Wall

The lateral orbital wall is created by two bones: the zygomatic bone and the greater wing the the sphenoid. This is the strongest of the walls of the orbit. Over there is a lateral orbit tubercle, which is an elevation of the orbital margin that the zygomatic bone and is an attachments for numerous important structures. These room the ligament the the lateral rectus muscle, the suspensory ligament the the eyeball (Lockwood ligament), lateral palpebral ligament, aponeurosis of the levator palpebrae superioris muscle, and the Whitnall ligament. 

Orbital Foramina, Fissures, and Ducts

Several openings in the bones of the orbit have anatomic and also clinical applications. 

The optic nerve, the ophthalmic artery, and also choroid plexus sympathetic fibers come from the middle cranial fossa and travel into the orbit via the optic foramen. The optic foramen passes through the lesser soup of the sphenoid bone and also travels inferiorly, anteriorly, and also laterally together it beginning the orbit.

The supraorbital foramen is ~ above the superior margin the the orbit and also contains blood vessels and the supraorbital nerve.  

The anterior ethmoidal foramen is in the frontoethmoidal suture, while the posterior ethmoidal foramen is situated at the junction that the orbit"s roof and medial wall. These 2 foramina transmit the anterior ethmoidal vessels and also nerve and the posterior ethmoidal vessels and also nerve, respectively. 

The nasolacrimal duct drains tears from the eye right into the worse meatus that the nose.

The infraorbital canal originates from the infraorbital groove. This contains the infraorbital nerve, which is the maxillary division of CN V.

The remarkable orbital fissure lies in between the greater and lesser wings of the sphenoid bone. Passing v the superior orbital fissure right into the orbit and above the common tendinous ring are the lacrimal nerve that CN V1, the frontal nerve the CN V1, CN IV (trochlear nerve), and the exceptional ophthalmic vein. Passing through the premium orbital fissure and also the usual tendinous ring space the superior and also inferior divisions of CN III (oculomotor), the nasociliary branch the CN V1, sympathetic root of the ciliary ganglion, and CN through (abducens).

The inferior orbital fissure lies ~ above the floor of the orbit. The premium border is the higher wing the the sphenoid, and the maxilla and palatine bone compose the worse border, with the zygomatic bone laterally. The zygomatic nerve and also the infraorbital nerve pass through this fissure and some infraorbital vessels.

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The infraorbital ship then travel along the floor of the orbit and pass v infraorbital groove anteriorly.<1><2><3>