hello everyone this is dr glenn fox and let's talk about the bony orbit
in this video we'll discuss the structure and relative location of the bony orbit
focusing on some of the major foramina fissures and fossae associated with the orbit and some of
the structures that are either associated or conveyed through those features so the
way that i conceptualize the bony orbit is a pyramid a four-sided pyramid the rim of the
orbit consists of three bones or is formed from three bones superiorly there's the frontal bone
laterally there's the zygoma or zygomatic bone and inferior medially we have the maxilla
now the four sides of the pyramid are going to be conveyed from that rim towards an apex which
is posteromedial so for instance we have the roof of the orbit the lateral wall of the orbit
the inferior or floor of the orbit and then the medial wall so here is the medial wall
there is the roof there is the lateral wall and there is the floor
it's probably best to uh to take a moment and appreciate the relative relationships of
the orbit to other regions of the skull so for instance the uh the roof of the orbit is going
to be in contact with the anterior cranial fossa that lateral wall with the middle cranial fossa
the floor with the maxillary sinus and the medial wall with the nasal cavity and some of
the paranasal sinuses in particular the ethmoidal air cells and the sphenoidal sinus as we'll see
the orbit serves as a location to house and protect the eye and the supportive musculature
and neurovasculature so not only will we have the eye but we'll have the various cranial nerves II,
II, IV V1 and V2 as well as VI running through the orbit
we'll also have ophthalmic arteries and veins within the orbit and we'll have
a generous amount of orbital fat or adipose connective tissues as well as other connective
tissues which help to protect those contents the bony orbit is an excellent place for those
extraocular muscles to attach so that they may tug upon the eye or the superior eyelid
so let's look at the roof of the orbit first the roof of the orbit consists of two bones
there's the frontal bone and the lesser wing of the sphenoid bone we'll see that the greater wing
comes into play with the lateral wall of the orbit so the frontal bone forms the front of the
cranium and there are a few features here that we should discuss so medially there's going to
be a trochlear fovea we can see that best in the cataveric image there that trochlear fovea
is a point of contact for the trochlea which is a cartilaginous ring which serves as a pulley
for the superior oblique muscle and we'll discuss this in greater detail when we discuss
the extraocular muscles laterally on the frontal bone we have the lacrimal fossa the lacrimal fossa
is where the lacrimal gland the gland which produces tears is going to sit
there is also within the frontal bone an irregularly shaped paranasal sinus known
as the frontal sinus which is going to be just on the other side of that frontal bone from the orbit
and as previously mentioned
if we go superior to the the frontal bone of the orbit will be within the anterior cranial fossa
so the sphenoid or the lesser wing of the sphenoid bone is going to play a role in the
roof of the orbit and its major feature that we're to be concerned with is that of the optic canal
the optic canal is going to be a continuity between the anterior cranial fossa
and the orbit and it's going to convey cranial nerve 2 the optic nerve as well
as the ophthalmic artery which is the major source of blood for the orbit
now let's look at the lateral wall of the orbit so the lateral wall of the orbit is going to look
like this its two major constituents are going to include the greater wing of the sphenoid bone
which is more posteromedial and the zygomatic bone which is more posterior lateral and lateral
this lateral wall is separated from the roof by the superior orbital fissure that superior
orbital fissure which i'm outlining here is quite a conduit between the middle cranial fossa and the
orbit and it's going to convey the bulk of the the nerves to the orbit so for instance cranial nerve
3 which is the oculomotor nerve which drives most of the extra ocular muscles cranial nerve four
the trochlear nerve which drives the superior oblique muscle the one which is the ophthalmic
branch of the trigeminal nerve is going to be conveyed through the superior orbital fissure
the abducens or cranial nerve 6 which innervates the lateral rectus nerve muscle is conveyed
through that fissure as well as the superior ophthalmic vein which is one of two major veins
the other being the inferior ophthalmic vein which drains the orbit and surrounding environments
the floor of the orbit consists of two bones the maxilla which is the lion chair of the floor
of the orbit which we can see there as well as a little bit of the zygomatic bone
there is also a very small minor contribution from the palatine bone as well the floor of the
orbit is separated from the lateral wall by the inferior orbital fissure which we can see here
that inferior orbital fissure is going to serve as a means to convey branches of the maxillary
nerve or the maxillary division of the trigeminal nerve which
traverse the orbit and these are going to include the infraorbital nerve and the zygomatic nerve
this inferior orbital fissure is also a continuity between the orbit and the pterygopalantine fossa
that pterygopalatine fossa is where one can find the pterygopalantine ganglion which is
the peripheral parasympathetic ganglion that serves the lacrimal gland so we can discuss that
in more detail when we discuss the lacrimal gland and that leaves the medial wall which
happens to have probably the the greatest contribution of a different bone to the orbit
the superior portion is the frontal bone and that's a small contribution and then inferiorly
from most anterior to most posterior we have the maxilla then we have the lacrimal bone
then we have the ethmoid and then we have a little bit of the sphenoid bone
the maxilla and the lacrimal bone are going to cradle a region known as the
nasolacrimal fossa mostly it's the lacrimal bone but there are parts of the maxilla there
and this nasolacrimal fossa is going to surround on you know two to three sides the lacrimal sac
the lacrimal sac is part of the lacrimal apparatus or system which is the system by which tears
which are secreted by the lacrimal gland move medially across the conjunctival sac of the eye
and are drained through that sac and ultimately into the inferior nasal meatus of the nasal cavity
which we'll discuss in a subsequent video that ethmoid bone is also going to be superficial
to other portions of the ethmoid bone which contain various cancellous or air-like sacs
of bone called the ethmoidal air cells which in their totality form the ethmoidal paranasal sinus
so we've discussed the orbit and its various bony surfaces the roof the floor and the
lateral and medial walls this is your summary slide thank you for your time