The upper edge of the cartilage is curled upon itself, being bent laterally so as to present on transverse section the appearance of a hook a groove or furrow is thus produced, which is open below and laterally, and this part of the canal is completed by fibrous membrane. in length, is formed of a triangular plate of elastic fibrocartilage, the apex of which is attached to the margin of the medial end of the osseous portion of the tube, while its base lies directly under the mucous membrane of the nasal part of the pharynx, where it forms an elevation, the torus tubarius or cushion, behind the pharyngeal orifice of the tube. The cartilaginous portion ( pars cartilaginea tubæ auditivæ), about 24 mm. It begins in the carotid wall of the tympanic cavity, below the septum canalis musculotubarii, and, gradually narrowing, ends at the angle of junction of the squama and the petrous portion of the temporal bone, its extremity presenting a jagged margin which serves for the attachment of the cartilaginous portion. The osseous portion ( pars osseo tubæ auditivæ) is about 12 mm. It is formed partly of bone, partly of cartilage and fibrous tissue Its length is about 36 mm., and its direction is downward, forward, and medialward, forming an angle of about 45 degrees with the sagittal plane and one of from 30 to 40 degrees with the horizontal plane. Occasional opening of the auditory tube keeps the air pressure the same on both sides of the tympanic membrane.The auditory tube ( tuba auditiva Eustachian tube) is the channel through which the tympanic cavity communicates with the nasal part of the pharynx. It's opened momentarily when we swallow or yawn, by the action of the tensor and levator palati muscles. The auditory tube, also called the eustachian tube, is normally closed. 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. We saw its emergence into the nasopharynx from the inside in Tape 4. The auditory tube enters the nasopharynx here. The narrowest part of the tube is here, where it emerges from the bone. This is the bony part of the auditory tube, connnecting with the tympanic cavity. 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. Here's the cartilage of the auditory tube. To see the auditory tube, we'll remove the tensor palati, and the lateral pterygoid plate. This one is the tensor palati, passing downward and forward to go round the hamulus. This one is the levator palati, passing down above the free border of the superior constrictor. It’s concealed between these two small muscles. This is the superior pharyngeal constrictor.
The external auditory meatus, and the tympanic cavity have been exposed, as in the previous dissection. In this deep dissection of the infratemporal region we've removed the zygomatic arch, the mandible, and all the muscles of mastication. 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. Its medial end projects beneath the mucosa of the nasopharynx. The cartilage of the auditory tube is attached to the base of the skull. 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 tunnel is quite short: it starts here, and ends here. It passes forwards and medially in a narrow tunnel in the bone. The auditory tube, which is where we're going next, begins at this opening at the front of the tympanic cavity. This is the lower part of the tympanic cavity with the three small bones removed. To see into the tympanic cavity we removed more bone here. Here's the bony external meatus, here's the groove for the anulus. To see the tympanic membrane we removed this part of the bone. After taking the mandible out of of the picture, we've been looking up at the underside of the petrous temporal bone from below. 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. Here in front is the opening for the auditory tube, which connects the tympanic cavity with the nasopharynx. We'll get a much better look at them later. This is the handle of the malleus, this is our first look at the incus, and the stapes. There's more of it back here, and up here, as we'll see. Here we're looking into the lower part of the tympanic cavity.