The external auditory canal is most curved in its cartilaginous portion. 618).Д¬oronal section through right ear, anterior view. The inner ear also contains the vestibular apparatus, the organ of balance (see p. The external and middle ear are part of the sound conduction apparatus, and the inner ear is the actual organ of hearing (see p. The auditory apparatus is divided into three main parts: external, middle, and inner ear. The patient must be oriented so that the semicircular canal of interest lies in the vertical plane. This caloric testing is important in the diagnosis of unexplained vertigo.

Irrigation of the auditory canal with warm (44вЊ) or cool (30вЊ) water can induce a thermal current in the endolymph of the semicircular canal, causing the patient to manifest vestibular nystagmus (jerky eye movements, vestibulo-ocular reflex). The bony semicircular canals are oriented at an approximately 45-degree angle from the coronal, transverse, and sagittal planes. The petrous portion of the temporal bone contains the middle and inner ear as well as the tympanic membrane. In severe cases, bacteria may pass from the mastoid air cells into the cranial cavity, causing meningitis. Bacteria may use this pathway to move from the nasopharynx into the middle ear. The mastoid process contains mastoid air cells that communicate with the middle ear the middle ear in turn communicates with the nasopharynx via the pharyngotympanic (auditory) tube.

The temporal bone consists of three major parts: squamous, petrous, and tympanic (see Fig.

External auditory meatus bone