O 
OBLIQUE ORBITAL LINE:
The radiographic shadow of the greater wing of the sphenoid bone, projected through the orbit.
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OBLIQUE VIEW:
A view or perspective that is rotated off axis from the three cardinal imaging planes:Sagittal - Coronal - Axial
OBTURATOR EXTERNUS MUSCLE:
Muscle which originates at the pubis, ischium, and the superficial surface of the obturator membrane, and inserts into the trochanteric fossa of the femur. It contributes to the lateral (external) rotation of the thigh.
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OBTURATOR FORAMEN:
The opening between the os pubis and the ischium.
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OBTURATOR INTERNUS MUSCLE:
Muscle which originates at the pelvic surface of the hip bone, the margin of the obturator foramen, the ramus of ischium, the inferior ramus of pubis, and the internal surface of the obturator membrane, and inserts into the greater trochanter of the femur. It contributes to lateral rotation of the thigh.
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OCCIPITAL ARTERY:
Originates from the external carotid and branches into the auricular, meningeal, mastoid, descending occipital, and sternocleidomastoid rami arteries.
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OCCIPITAL BONE:
The bone situated at the inferior and posterior portion of the cranium, articulates with the two parietal bones (at the lambdoid suture) and the temporal bones as well as the sphenoid bone and the atlas (C1).
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OCCIPITAL LOBE:
The cerebral lobe from the posterior pole to the parietooccipital fissure medially and continuous with the parietal lobe laterally. The occipital lobe is immediately above the tentorium, and is supplied by the posterior cerebral artery.
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ODONTOID PROCESS (DENS) (C1):
The "tooth-like" projection from the superior surface of the axis, which ascends to articulate with the atlas, allowing the head to rotate on the cervical spine.
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OLECRANON PROCESS:
The bony projection of the distal ulna at the elbow, which helps form the trochlear notch. On extension of the arm, the olecranon "hides" in the olecranon fossa of the distal humerus.
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OPACIFIED:
Made to be opaque to X-ray irradiation, due to the introduction of contrast material - as in a barium study (Upper GI, Barium Enema), arteriogram, myelogram, etc.
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OPHTHALMIC ARTERY:
Originates from the internal carotid and branches into the lacrimal, supraorbital, central artery of the retina, ciliary, posterior and anterior ethmoid, palpebral, supratrochlear, and dorsal nasal arteries.
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OPTIC NERVE:
The second cranial nerve, responsible for the special sensation of sight. This is not really a "nerve", but is actually a post-synaptic white-matter tract that connects the retinal ganglion cells to the occipital (visual) cortex, via the chiasm, lateral geniculate body, and the optic radiations.
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ORAL CAVITY:
Cavity of the mouth including the inside of the cheek, palate, oral mucosa, teeth, tongue, and glands that open into the cavity itself.
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OROPHARYNX:
The portion of the pharynx below the soft palate and above the upper edge of the epiglottis.
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OSTIA:
(ostium pl.) The opening of a tubular organ or between two cavities.
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OUTER TABLE OF SKULL:
The outer layer of compact bone, part of the flat bones of the skull.
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Bug Report
Portions © 1997, 2002 J.G. Smirniotopoulos, M.D. and others.