Where it is
Under the skull, behind the jaw joint.
- Layer
- Skeleton
- System
- Axial skeleton
- Region
- Head
What it is and what it does
A rounded bony swelling of the tympanic part of the temporal bone, large in carnivores. It encloses the ventral part of the middle ear cavity, with the eardrum and the three ossicles; from here the inner ear begins, with the cochlea and the vestibular labyrinth (hearing and balance).
It lies between the retroarticular process and the paracondylar process of the temporal bone. In carnivores, rodents and rabbits it is large and rounded, hence the name; in humans it is absent, and in the horse and ruminants it is small or absent. A thin wall of bone, the septum bullae, separates it from the upper part of the tympanic cavity.
In the dog, the middle ear cavity has a small epitympanic recess, above, and the large bulla, below; it is filled with air and lined by a ciliated epithelium. The malleus, the largest and outermost of the three ossicles, is attached to the eardrum; the stapes, the innermost, lies horizontally with its base facing inward. The facial nerve leaves the skull right next to the bulla, through the stylomastoid foramen, which is why bulla surgery takes care to avoid it.
Worth remembering
From here the inner ear begins, with the organs of hearing and balance.
Names
- Latin term: bulla tympanica.
- In Romanian: Bula timpanică (Romanian page).