Normal Structure and Function of Ears

Hearing is one of the fundamental sense. Ear also known as the vestibulocochlear organ, is subdivided into three parts namely external, middle and inner ear. Auricle and external acoustic meatus comprise external ear. Sound waves are transmitted from the external ear to the middle ear. In dogs, breed-specific variances of external ear is noticeable. The auricle has a funnel-like shape which helps in sound collection. Auricle is divided into the proximal conchal cavity and distally located scapha. Anthelix divides the conchal cavity from the scapha and is located close to the conchal cavity. External acoustic meatus is made up of a proximal osseous portion and a distal cartilaginous portion. The cartilaginous portion of carnivores is relatively long and curved which hampers the passage of the straight otoscope for examination. The tympanic membrane consist of two parts, namely the pars flaccida and the pars tensa. The middle ear comprises the auditory ossicles (malleus, incus and stapes), muscles and auditory tube. Tympanic cavity is contained in the petrous temporal bone and has dorsal (epitympanicum), middle (mesotympanicum) and ventral (hypotympanicum) section. Auricular ossicles are located in the dorsal portion. The tympanic membrane is located on the lateral wall of the middle portion. The tympanic bulla is known as the ventral hypotympanicum. Internal ear has membranous and osseous labyrinth. The membrane labyrinth is filled with endolymph and includes the vestibular labyrinth which houses the receptor organ for balance and cochlear labyrinth containing the organ of hearing. The osseous labyrinth consists of vestibule, semicircular canals and cochlea. While defects in the inner ear may result in sensorineural hearing loss, defects in the outer, middle, and middle ear can cause conductive hearing loss. Therefore, it is crucial to research the anatomy and physiology of the ear. This chapter's main objective is to explore the fundamental anatomy and physiology of numerous components of the canine ear that plays a vital role in hearing.