Here we're looking into the lower part of the tympanic cavity. There's more of it back here, and up here, as we'll see.
This is the handle of the malleus, this is our first look at the incus, and the stapes. We'll get a much better look at them later. Here in front is the opening for the auditory tube, which connects the tympanic cavity with the nasopharynx.
We’ll look at the auditory tube, then come back to the tympanic cavity, but first let’s look at a dry bone specimen to see where we’ve been and where we’re going next. After taking the mandible out of of the picture, we've been looking up at the underside of the petrous temporal bone from below. To see the tympanic membrane we removed this part of the bone.
Here's the bony external meatus, here's the groove for the anulus. To see into the tympanic cavity we removed more bone here. This is the lower part of the tympanic cavity with the three small bones removed.
This is as far as we’ve come till now. The auditory tube, which is where we're going next, begins at this opening at the front of the tympanic cavity. It passes forwards and medially in a narrow tunnel in the bone. The tunnel is quite short: it starts here, and ends here.
Only the lateral third of the auditory tube goes through bone; its medial two thirds pass though a partial tube of cartilage that’s represented by this added material. The cartilage of the auditory tube is attached to the base of the skull. Its medial end projects beneath the mucosa of the nasopharynx.
To see the auditory tube itself, we’ll go back to a dissected specimen. In this deep dissection of the infratemporal region we've removed the zygomatic arch, the mandible, and all the muscles of mastication.
The external auditory meatus, and the tympanic cavity have been exposed, as in the previous dissection. Here's the lateral pterygoid plate. The nasopharynx is here. This is the superior pharyngeal constrictor. Its upper border is here.
The auditory tube is up here. It’s concealed between these two small muscles. This one is the levator palati, passing down above the free border of the superior constrictor. This one is the tensor palati, passing downward and forward to go round the hamulus.
To see the auditory tube, we'll remove the tensor palati, and the lateral pterygoid plate. Here's the cartilage of the auditory tube. Here beneath it is the tube itself. To see the auditory tube all the way to the tympanic cavity we'll open it along this line, and remove this part of the bone.
This is the bony part of the auditory tube, connnecting with the tympanic cavity. This is its cartilaginous part. The narrowest part of the tube is here, where it emerges from the bone.
The auditory tube enters the nasopharynx here. We saw its emergence into the nasopharynx from the inside in Tape 4. Here's the nasopharynx, here's the back of the nasal cavity, here's the soft palate, here's the opening of the auditory tube.
The auditory tube, also called the eustachian tube, is normally closed. It's opened momentarily when we swallow or yawn, by the action of the tensor and levator palati muscles. Occasional opening of the auditory tube keeps the air pressure the same on both sides of the tympanic membrane.