Main Model
Internal ear : 15a Lateral bony ampulla
Semicircular Canals
The semicircular canals (anterior, posterior, and lateral) communicate with the vestibule of the bony labyrinth. The canals lie posterosuperior to the vestibule into which they open; they are set at right angles to each other. The canals occupy three planes in space. Each semicircular canal forms approximately two thirds of a circle, and is approximately 1.5 mm in diameter, except at one end where there is a swelling, the bony ampulla. The canals have only five openings into the vestibule because the anterior and posterior canals have one limb common to both. Lodged within the canals are the semicircular ducts.
Semicircular Ducts
Each semicircular duct has an ampulla at one end containing a sensory area, the ampullary crest (Latin crista ampullari). The crests are sensors for recording movements of the endolymph in the ampulla resulting from rotation of the head in the plane of the duct. The hair cells of the crests, like those of the maculae, stimulate primary sensory neurons, whose cell bodies are in the vestibular ganglia.