Equine Special Senses - Horse Anatomy

Ear

The ear is a paired sensory organ, that is involved in both hearing and balance. For this reason, the ear is known as the vestibulocochlear organ. Sound waves that are transmitted into the ear provide a mechanical stimulus. These mechanical stimuli are then transferred into electrical signals by the cochlea. Neuroreceptors in the ear allow the horse to gain a perception of position and movement. Anatomically, the ear can be looked at in three parts:

1. Outer ear - pinna and auditory canal

2. Middle ear - contains the malleus, incus and stapes bones - known as the ossicles

3. Inner ear - contains the membranous and bony labyrinths, and the cochlea

Outer Ear

Outer Ear - Copyright David Bainbridge

The pinna (or auricle) is defined as the outer projecting part of the ear, that is the part of the ear that can be seen. It consists of the auricular cartilage, surrounded by skin, which allows for flexibility and elasticity. The auricular cartilage connects to scutiform cartilage, which itself connects to annular cartilage, which allows for articulation. These cartilages fit into the bony passage of the ear canal - also called the external auditory meatus, which leads to the tympanic membrane. This is the deepest boundary of the outer ear. Muscles around the base of the ear that are attached to the skull allow movement of the pinna, so the ear can be directed to the source of sound:

Muscle	Origin	Innervation	Function
Preauricular	Deep temporal fascia	Auriculopalpebral branch of facial nerve (cranial nerve VII)	Moves the ear cranio-laterally, so the pinna is facing forwards
Ventroauricular	Laryngeal fascia	Retroauricular branch of facial nerve (cranial nerve VII)	Moves the ear laterally
Postauricular	Medial cervical raphe	Retroauricular branch of facial nerve (cranial nerve VII)	Moves the ear caudo-laterally, so the pinna is facing backwards

Central Auditory Pathways

===Vestibular Receptors and Balance