Walls of vestibule

The walls of vestibule form part of the bony labyrinth. They impart a box-like appearance to the vestibule. The bony walls of vestibule enclose two important components of membranous labyrinth, namely the utricle and the saccule.

Some of the salient features found within the vestibular walls, include the openings of semicircular canals, the vestibular aqueduct, oval and round windows.

A total of three semicircular canals can be seen entering into the vestibule. Each canal opens at its two ends into the bony vestibule, however, since two of the semicircular canals–the anterior and posterior ones–fuse with each other at one end, therefore despite there being three semicircular canals, only five openings can be seen within the walls of vestibule.

Next, a narrow bony canal, called the vestibular aqueduct, can be seen emerging from the bony vestibular wall. It traverses backwards through the temporal bone and eventually opens up into the posterior cranial fossa, onto the posterior surface of the petrous part of temporal bone. The aqueduct hosts within it, an endolymphatic duct and a sac, which are both parts of the membranous labyrinth.

Additional structures found within the walls of vestibule include the oval and round windows. Oval window refers to a space which is covered over by the footplate of stapes from the side of the middle ear cavity. Whereas, the round window is a small gap within the vestibular wall that is sealed off by a secondary tympanic membrane and marks the base of the scala tympani.