hello osteology friends it is dr. Alsup again to talk a little bit more about the osteology
associated with their cranial cavity and brain session now we are going to focus on the cranial
fossa and specifically we're going to be able to identify these different and then specific
structures within these regions and there are a lot there are a lot of foramina so we're going
to talk about how to identify them as well as why we want you to know them so what's traversing
them so let's get started so before I get started let's talk about the view and we are looking at a
superior view of the basal cranium so the brain would have been sitting right in here and that
is going to show kind of this stair-step fashion of the fossae so this is a little bit higher when
we're talking about the more anterior portions the middle cranial fossa will be intermediate and then
you'll have this really deep posterior cranial fossa which makes sense because you the cerebellum
would be sitting in this region during life so you're gonna have a much deeper or your lowest
step associated with the posterior cranial fossa all right so let me take a minute really quickly
to kind of draw a few lines to help us get an idea of these boundaries and then we'll talk about each
one okay so the anterior cranial fossa will be between the front or the anterior portions of
the frontal bone back to the lesser wings of the sphenoid and so these right here are the lesser
wings of the sphenoid it these are going to be as the name would suggest lesser are smaller than
these larger greater wings of the sphenoid that's kind of making that butterfly shape right there so
the anterior cranial fossa is between the front of the frontal bone as well as the lesser wings the
middle cranial fossa will go from the lesser wings of the sphenoid to the apex or the top portion of
the petrous parts or the petrous parts of the temporal bone you'll hear it either way so this
kind of top portion of the petrous part of the temporal bone and then the posterior cranial fossa
will be between that apex of the petrous part to the back or the squamous portion of the occipital
bone so here again is the anterior cranial fossa this will be the middle cranial fossa and this
will be your posterior cranial fossa which is your deepest of the fossae all right so let's
talk about the structures within the anterior cranial fossa first so recall again I always
kind of think of those boundaries so here is that lesser wing of the sphenoid - the frontal bone and
now we are in the anterior cranial fossa now I am outlining what we can see of the ethmoid bone in
this particular view so we'll see the ethmoid bone in numerous other regions you'll see a portion of
it within the orbit you'll see portions of it playing the role and nasal septum but what I've
just outlined here is the ethmoid bone and it's a fairly distinctive looking area you have this
projection right here which is referred to as the crista galli the crista galli is going to be the
anterior attachment for the fal cerebri which is one of your dural partitions in fact it's your
largest oral partition a very distinctive next two on either side of the crista galli are all
the small holes or foramina specifically we refer to these as the cribriform foramina and this is
how those olfactory nerve axons are heading back towards the brain region so olfactory nerve is
your cranial nerve one so those are this is how those accents are traversing through the region
so very distinctive like is very sieve like in terms of all these small foramina on either
side of the crista galli okay back towards uh this region so we're into the
sphenoid bone now I will once again identify your lesser wings here and then kind of right
kind of more in the middle region here you can see where we're starting to get some dark area
right here indicating that we're heading into a space specifically we're heading into a canal
which are your optic canals your optic canals are going to allow the optic nerve or cranial
nerve two to enter into the orbit as well as the ophthalmic arteries which are also heading towards
the orbit just a note here that while we had the optic canals categorised as part of the anterior
cranial fossa based on what the categorization is in grey's anatomy you may see another literature
that the up two canals are often defined as being part of the middle cranial fossa so don't don't
get too bogged down about that just understand and be able to identify where the optic canals
are okay moving into the middle cranial fossa this area is a bit more complex in terms of the
in terms of the foramina associated with this region so here is your middle cranial fossa the
first thing we're going to identify is the most anterior structure of the middle cranial fossa and
these are your superior orbital fissures which are going to be located I always like to think of
them as kind of underneath those lesser wings of the sphenoid so underneath the lesser wings
of the sphenoid sometimes it can be difficult to see them in this superior view we'll have other
views and subsequent videos where you're looking at it through the orbit it's a little bit easier
to see there now the superior orbital fissure as its name would suggest is heading towards
the orbit so it allows things to traverse this region into the orbital region so a lot of the
nerves that you need to get into the orbit like oculomotor trochlear abducens as well as v1 or
your first division of the trigeminal nerve will also traverse the superior orbital fissure as well
as the ophthalmic veins all right let's talk about this region right here in the middle this whole
complex right here is referred to as the sella turcica and you can see that the sella turcica
means turkish saddle you can see that you have kind of this saddle like region right here and
this divot right here or this fossa is referred to as the hypophyseal fossa and this is where
portions of the pituitary gland sit and so it makes sense that this whole area is fairly complex
Osteologically because you need to afford a lot of protection to that very important pituitary
gland and so sometimes pituitary gland is referred to as the hypothesis and so that's why you have
the hypophyseal fossa sometimes you see this spelled with an e in fact often times you'll see
it spelled with an E in Grey's Anatomy I think just recently updated the excuse me the terminological
anatomica which is kind of where we get the anatomical names kind of the end-all-be-all has
just transitioned to this type of spelling here so if you see it with any it means the same thing it
doesn't really matter as long as you can identify okay so let's go back to this greater wing region
of the sphenoid like I said it forms this nice butterfly shape here and let's talk about some
of the some of the foramina here so we'll start with this nice circular foramina here these are
the foramen rotundum so the foramen rotundum is going to allow for v2 or your maxillary nerve or
your second division of the trigeminal nerve to exit the skull so those three names that I just
said all mean the same thing so that is what's exiting through the foramen rotundum the more
oval shape foramen here is going to be the foramen ovale and the foramen ovale is
going to allow for v3 or your mandibular nerve or your third division of the trigeminal nerve
to exit the skull and v3 is the larger and the or excuse me the largest division and so that's why
you have a slightly larger foramen here and then lateral and really small you're going to have the
foramen spinosum the framing spinosum is going to allow the middle meningeal artery to a send
or enter into the skull so middle meningeal artery we'll talk a little bit about that later but it's
going to be one of the dominant supplies for the meninges so it has to get into the skull so that
is how it is entering okay the posterior cranial fossa as we mentioned is going to extend from the
apex of the petrous part back to the occipital bone this whole region right here is considered
the petrous part it's a really neat region you actually have your middle in your inner ear housed
within the petrous part of the temporal bone and this line that I keep drawing is kind of the top
or the apex of the petrous part now I kind of write around this region and this is difficult
to see as well you're gonna have two openings into that petrous part so entering into the bone here
and these are your internal acoustic meati. Meatus is singular the IAM is going to allow the facial
nerve as well as vestibular cochlear so cranial nerve seven and eight to enter into the petrous
part of the temporal bone okay moving along so there's that jugular foramen that we have talked
about over and over again that's going to be right about here your hypoglossal canal are going to be
right in this region we talked about this in one of the other videos as well like I mentioned there
I always try to find the foramen magnum and then head towards the basilar part of the occipital and
it'll be kind of hiding out right in there that will allow cranial nerve 12 or your hypoglossal
nerve to exit okay so these are some of the foramina of the cranial fossa and obviously the
boundaries associated with them as you review this material and if any questions come up always feel
free to reach out to me or any of my colleagues please have a wonderful rest of your day