hi let's talk about the osteology of the orbit the orbit is the region of the cranium where the eye
and supporting structures and neurovascular of the I live colloquially we would refer to this
is the eye socket and it is comprised of several different bones I'd like to start here with this
color-coded skull so that we can best visualize how these bones relate to one another so the the
first poem that I'd like to draw your attention to it forms the front of the cranium there go the
the frontal bone and it is going to be largely the roof of the orbit so I'll just outline the portion
of the frontal here that's contributing to the orbit and you can see that the overabundance of
the the roof of the orbit is is formed by this bone we also if we move inferior from the bone
right here have the lacrimal bone the lacrimal bone gets its name not from the lacrimal gland
because the lacrimal gland is found up in the lacrimal fossa of the frontal bone but because
this is the osseous feature through which tears or the secretions of the lacrimal gland are drained
through the nasolacrimal duct and so looking at this bone posterior lis here you know thicken
this this would be the lacrimal crest or the posterior lacrimal crest and there's also just a
slight groove there called the lacrimal groove now you may notice that on the next bone that we'll
discuss there is also a lacrimal groove so there is a lacrimal groove of the lacrimal bone and
there is a lacrimal bone of the maxilla but let's let's talk a little bit about the the maxilla
before we go into any particular details so the maxilla is famous for being the superior of the
two teeth baring bones of the skull and in terms of its role in the orbit it's largely the floor
of the orbit so here we can see the maxilla and it's a roll of floor for the orbit we can also see
that there is a nice extension of the maxilla here this is the frontal process of the maxilla that's
separating the lacrimal bone from the nasal bone a lot of osteology is named fairly well so in this
case this frontal process of the maxilla is named because it's reaching out and coming into contact
with the frontal bone you should think about process names because they might describe either
the shape of the feature the relationship of that feature to some other feature or they might
be even in direct contact with the feature for which they're named regardless if you look just
a jacent to the lacrimal groove of the lacrimal bone there's going to be another groove and it's
hard to tell this because that frontal process is in the way but there's another groove on the
maxilla also called the lacrimal groove and the two lacrimal grooves are adjacent to one another
moving right along or I should say let's let's move clockwise we have the zygomatic bone so the
zygomatic bone here is the cheekbone sometimes just called the zygoma and in terms of the orbit
it is largely going to be the lateral wall of the orbit now the the feature or the surface
of the zygomatic bone that comes into play for the orbit is no as the orbital surface so that
is well-named I suppose and if we look at the very back of the orbit we see that that posterior
wall everything that is here in yellow is the sphenoid bone the sphenoid bone is a remarkably
complex and beautiful bone that you can see there are many different views of the skull
much of it is going to be obscured by other elements of anatomy but it's a very important
central bone that's really tying together a lot of osseous muscular and neurovascular features
we'll will go into greater detail regarding via the sphenoid bone but if we continue our tour
you might notice and let me erase this here so that we can better see you might notice that
just between the sphenoid and the lacrimal bone there is another bone to be seen and
this is the ethmoid the ethmoid forms the medial wall of the orbit now all of these are just very
rough description so medial wall of the orbit lateral wall of the orbit floor roof you know
we can see how some of these other bones are also going to contribute to these structures it's also
important to note that the orbit isn't a cube it's not a box it's not a perfect geometrical shape by
any stretch of the imagination we conceptualize the orbit as sort of a medially facing cone and
so the the apex of that cone is there and this is an important lesson to learn with respect
to the extraocular muscles in particular the the rectus muscles the superior inferior because this
arrangement of where these muscles are attached to relative to the eye is going to have a profound
effect on the actions of these muscles that go beyond the basic insertion points on the sclera
of the eye so think about this relationship this structure of the orbit as you consider
the actions of the extraocular muscles that will be exceedingly important also important
to note is that the paranasal sinuses are going to be in close communication with the orbit in
in various ways but just you know geographically the frontal sinus within the frontal bone is going
to be abutting the orbit the ethmoidal sinuses going to be abutting both orbits the sphenoid
sinus which is even further back posterior will be abutting the orbits and then the maxillary
sinus is going to be abutting the orbits so all of those paranasal sinuses where as they communicate
with the nasal cavity are also going to be very close to the orbit now let's let's look at the
frontal bone here recall you know it is the front of the neurocranium and there are two
features that that we'd really like you to to understand here with the frontal bone the first
is the lacrimal fossa the lacrimal fossa is the osseous feature that denotes where the lacrimal
gland lives and the lacrimal gland is a lateral feature in the superior orbit so this indentation
here on the frontal bone is the lacrimal fossa we also have a trochlear fovea trochlear fovea
recall that the trochlear nerve cranial nerve 4 serves the superior oblique muscle this pure
oblique muscle is running from the apex of the orbit oops from the apex of the orbit along the
medial wall and it's tendon runs through the trochlea which attaches there to this trochlea
fovea trochlear fovea and it runs over to the the sclera on the superior surface of the eye
and so that trochlear fovea is associated with the trochlea there and sometimes we could even see a
tiny little spine of a bone that's associated with the attachment of the ad the trochlea there all
right yeah the sphenoid bone again the sphenoid is a fairly secretive bone we catch glimpses of
it it's most significant in the orbit as the the posterior wall of the orbit and there are a couple
of features here that we're going to want to know about and these are very important features for
the conveyance of neuro vasculature so let's start here that's the optic canal the optic
canal is the osseous canal through which cranial nerve - that's the optic nerve as well as the
opthalmic artery runs so cranial nerve two and the ophthalmic artery run through the optic canal that
leaves us with the orbital fissures there's a superior orbital fissure and an inferior
orbital fissure to denote their relationships to one another so here is that superior orbital
fissure there is that inferior orbital fissure the the superior orbital fissure is really within
the sphenoid bone whereas the inferior orbital fissure is between the the sphenoid bone and
the the maxilla running through that superior orbital fissure are quite a lot of features so
we have both the superior and inferior divisions of cranial nerve three that's the oculomotor nerve
we also have cranial nerve for the trochlear nerve we have branches of V 1 which is the
ophthalmic nerve or the ophthalmic division of the trigeminal nerve and then we also have the
abducens which is cranial nerve 6 so if you recall 3 4 & 6 are all serving those extra ocular muscles
in addition we also have sympathetic fibers that make their way through that
superior orbital fissure and then finally elements of the ophthalmic
veins and conceptually there are superior and inferior divisions of the ophthalmic
veins and generally branches of both go through that superior orbital fissure
the inferior orbital fissure has significantly fewer things running through it so that inferior
orbital fissure down here is going to convey zygomatic branches of V2 V2 which is the
mandibular nerve the thrust of it is actually moving inferior to the the orbit just below
the floor of the orbit on the way out to to come out the infraorbital foramen is the infraorbital
nerve if you recall that you know there's there's also branches of V2 which are going down to serve
the maxillary teeth etc so V2 is is kind of a mid-face a deep mid-face nerve for that and then
also at times the inferior ophthalmic vein will run through the the inferior orbital fissure as
well so that inferior ophthalmic vein is a little promiscuous with respect to its root it could
be the superior orbital fissure it could be the inferior could actually be both if there are two
of them so that is the elements of the sphenoid that participate in the orbit let's talk a little
bit about the ethmoid so the ethmoid like the sphenoid is a very secretive bone it's probably
an even more secretive bone than the the sphenoid some of the elements that you're going to want to
know about include this perpendicular plate of the ethmoid as well as the superior and middle nasal
caca we can't see the superior one it's going to be higher up there so those are the elements of
the ethmoid that relate here at least to this particular view and we'll see how the orbit in
the nasal cavity relate to one another in terms of the the neurovascular that that are held in
common between these two regions also the orbital plate of the ethmoid so looking at the the orbit
from this view so keeping in mind that the maxilla is the floor the frontal is the roof and then here
is our Beth Lloyd bone and the ethmoid separates from the sphenoid about there sometimes seeing
these sutures are imperfect and then between the frontal and the ethmoid it's about there so the
orbital plate is this surface that be the the surface of the ethmoid that's forming the the
medial wall of the of the orbit and then we have two fur Aminah there is a posterior ethmoidal
foramen in an anterior ethmoid illumine and these are going to be for the conveyance of
the ethmoidal neurovascular Chur so osteology is usually exquisitely named so running into that
posterior ethmoidal foramen will be things like the posterior ethmoidal artery and nerve and vein
running into the anterior will be the anterior ethmoidal artery and anterior ethmoid 'el nerve
these will take different courses as they move through the ethmoidal and we also have this view
of the ethmoid bone and from this view of the ethmoid bone we can see I'll just outline it for
you the cribriform plate the cribriform plate is very much full of these holes these are the
olfactory fir Aminah and it's through these holes that the olfactory nerves run so cranial nerves
one separating left side from right side there is this crista galli so Christa is a comb and gali is
meaning a chicken so this is the the roosters comb and this is going to separate the olfactory bulbs
on top of the cribriform plate on either sides so in this video we discussed the the bony orbit we
talked about the bones which comprise the orbit so the the frontal the lacquer mole the maxilla the
zygomatic the sphenoid and the ethmoid and some of their features thank you very much for your time