 I'd like to offer you the opportunity to look at the next series of about 10 slides through the anatomy and stop the recording and quiz yourself on the anatomy before I describe the anatomic structures. So they will be labeled either with the letters or with numbers, and you can quiz yourself and see how well you already know the anatomy and then maybe even correct me. So here's an initial axial scan, and as we look at the anatomy of the extra auditory canal, we will start with that, but we will continue into the anatomy overall of the temporal bone. As I said, I think it's always good to review this. There's always important things that we can each teach each other. On this axial CT scan in bone window, we identify A as the helix of the ear. This is a portion of the external ear. B as the cartilaginous portion of the extra auditory canal. We're starting with the bony portion across here. This is right at the junction between cartilaginous and bony portion. C as the tympanic membrane, and where actually the arrow is, is in the middle ear cavity, but you can faintly see the tympanic membrane. If you're doing CT scans that are two millimeters thick or less, you should routinely be able to see the tympanic membrane. D here is the anterior epitimpanic space. This is a portion of the middle ear cavity that is residing further anterior to the anterior epitimpanic space. And E represents the bony portion of the external auditory canal. We're flipping to look at the right side of the temporal bone and the skull base. So again, these are numbered for you. You can quiz yourself and put a stop to the recording at this juncture and write down your answers, or you can follow along with me. Number one represents the fremen ovale. Fremen ovale is the egress of the third division of the fifth cranial nerve. The fifth cranial nerve is called the trigeminal nerve, and the third division of the fifth cranial nerve is the mandibular nerve, and it goes out through the fremen ovale, represented as number one. Number two here is fremen spinosum. It's just posterior lateral to fremen ovale, and it transmits the middle meningeal artery as well as some nondescript nerves. Number three you should identify as the carotid canal. We are just at the level of the fremen lacerum, which is going to be found here as the pietrus portion of the internal carotid artery runs over top of fremen lacerum. Number four is the jugular fremen. This is obviously where the jugular vein is transmitted, as well as the cranial nerves 9, 10, 11 in pars nervosa and pars vascularis of the jugular fremen. Number five we see the sigmoid sinus junction with the transverse sinus, and some people refer to the bone overlying it as the sigmoid plate. Again, I'll give you a moment to determine whether you want to identify the anatomy. So here we go. Number six is the seventh cranial nerve. Actually the descending portion of the seventh cranial nerve is a little bit more posterior to this arrowhead. However, you notice that there are these other little areas of soft tissue that are just adjacent to the seventh cranial nerve. The one that the arrow is actually pointing to is the cortotempani nerve. This circles back after leaving the stylo-mastoid fremen and comes back up the temporal bone for a brief period of time as a soft tissue process just adjacent to the seventh cranial nerve. Number seven on first blush might look like a small internal auditory canal. This is not the internal auditory canal. It's below the internal auditory canal and it represents the cochlea aqueduct. So the cochlea aqueduct is communicating with the posterior fossa subarachnoid space and it is a communication for the CSF space from the intracranial compartment communicating to the cochlea. Next slide. Number eight is the basal turn of the cochlea. And number nine represents that little bony hillock that overlies the cochlea basal turn and that is the cochlear promontory. So this little bony prominence on number nine is the cochlear promontory. On number 10 we are pointing to the descending portion of the facial nerve. Let's look at a little bit more anatomy on the same side that has not been labeled. Here is the lateral aspect of what was seen on the previous slide of the cochlear aqueduct. So this is a portion of the cochlear aqueduct coming towards the cochlea. What you're seeing posteriorly and medial to the cochlear promontory is the beginning of the round window. The round window is an area of air that leads to the basal turn of the cochlea. Its importance is that it is through the round window that cochlear implants are inserted. From the round window we can move posteriorly and we come to this airspace which is medial to the seventh nerve and this is the sinus timpani. The sinus timpani and the bone that overlies the seventh nerve which is the pyraminal eminence and then the facial nerve recess represent anatomy of the hypotimpinum. This bony area that connects the round window to the sinus timpani is the subiculum. Let's continue to the next level above where we started down low at the cochlear aqueduct and now we're moving our way superiorly. What we're seeing is a lot of the anatomy of the middle ear cavity. So number 11 represents that anterior epitimpinic space. It's a little outpouching of the middle ear cavity. Number 12 represents the neck of the malleus and you see a small soft tissue structure which is leading to the neck of the malleus from the cochlear form process which is this area over here and this is the tensor timpani muscle. Number 13 is the long process of the incus. It's the second little bright dot of the middle ear ossicles. So we have the neck of the malleus and the long process of the incus and this is going to communicate with the stapes at the oval window. Number 15 you should recognize as that airspace I mentioned previously which is the sinus timpani and then media to that is the pyraminal eminence and then I'm sorry lateral to that is the pyraminal eminence and then lateral to that is the facial nerve recess with the facial nerve residing just below here. Here we see a little bit of the cochlear aqueducts communication with the turns of the cochlea and this is one of the semicircular canals and we're just getting into cutting a portion of the vestibular aqueduct. Okay continuing onward. Number 16 again the same anterior epitmpanic recess. Number 17 is on that muscle that tensor timpani muscle which leads from the cochlear form process to the neck of the malleus. Here we are seeing the stapes. It's very faintly seen even using one millimeter thick slices. The stapes is such a small structure that we can barely see the crura. This is the posterior cruce of the stapes. This is the anterior cruce of the stapes and the long process of the incus is going to communicate with the stapes at the incudos the PDO joint. Number 19 is a representation of the facial nerve again sinus timpani, pyraminal eminence, facial nerve. This is one of some of the structures of the hypotimpinum and number 20 is the vestibular aqueduct. Some people will use the term endo lymphatic sac that's the salt tissue that is associated with the vestibular aqueduct which is that bony kind of canal. Okay so again you can quiz yourself and you can listen to me. Number 20 is a portion of the cochlea. What we're seeing here is just cutting through the apical turn of the cochlea. This is the middle turn of the cochlea and on a previous slice when I was showing the round window we saw the basal turn of the cochlea. So those are the three turns, basal turn, middle turn and apical turns of the cochlea. We're actually showing very nicely this area which leads from the internal auditory canal to the cochlea. This is the cochlear aperture. The cochlear aperture leading from the internal auditory canal to the cochlea. And this little amorphous hyper-densy within the cochlea is going to be part of the medialis which is effectively the skeleton of the cochlea. Number 21 is pointing to mastoid entrum, some of the mastoid air cells. Number 22 is pointing to the internal auditory canal. And 23, I will give you triple credit if you're able to identify this little structure. This little structure is the singular canal. It transmits the singular nerve which goes to the semi-circular canal from the internal auditory canal. It's one of the branches of the vestibular nerves. And it's a nicely demonstrated small canal that is one that they try to avoid when they do vestibular schwannoma resections because if they hit that nerve, postoperably the patients often have vertigo or persistent dizziness. We're nicely seeing the vestibular aqueduct again over here. And you also have a nice view of the stapes, anterior cruces, posterior cruces, and that portion of the superstructure of the stapes that we call the capitellum which is articulating with the long process of the incus. This is our neck of malleus, tensor tympani muscle, long process of incus. We are continuing further superiorly. On section 24 we are seeing what is sometimes referred to as the ice cream on the ice cream cone. The ice cream on the ice cream cone, this is the ice cream cone, the ice cream is the head of the malleus and the ice cream cone here is the short process of the incus. That's number 24 is the head of the malleus. Number 25 is the vestibule and from the vestibule we will identify the semicircular canals. Number 26 is pointing to the tympanic portion of the facial nerve or the horizontal portion of the facial nerve. Excuse me. 27 we are seeing the generic ganglion. This is at the junction between the fallopian canal portion of the facial nerve or the labyrinthine portion of the facial nerve. Number 28 with the tympanic portion of the facial nerve. At that junction one has the geniculate ganglion. This is what is sometimes called the first genu, the first turn when the labyrinthine portion initially goes anteriorly to the geniculate ganglion, the seventh nerve ganglion and then moves horizontally across the tympanic portion of the facial nerve. All these are portions of the facial nerve. The intracanelicular portion is the part in the internal auditory canal, the labyrinthine portion in the fallopian canal, pre-ganglionic, pre-geniculate ganglion and then the posterior, the post-geniculate portion or tympanic or horizontal portion of the facial nerve. Again vestibule, we are getting a little bit of the lateral semi-circular canal. We are just hitting a portion of the posterior semi-circular canal. We are moving further superiorly. Here we see the genu of the superior semi-circular canal. Remember it is going to loop up and back down and so we are seeing the anterior and posterior genu of the superior semi-circular canal with a little portion of the posterior semi-circular canal cut in cross section here. This is a big mastoid air cells. This little canal which goes between the anterior and posterior limbs of the superior semi-circular canal transmits the arcuate artery. It is called the arcuate canal or semi-arcuate canal going between the arches of the superior semi-circular canal.