The structure indicated is the lateral rectus muscle.

This muscle is one of six muscles that are involved in the movements of the eye. The muscles which move the eye are referred to as the extraocular muscles, these include:

• Superior rectus
• Inferior rectus
• Lateral rectus
• Medial rectus
• Superior oblique
• Inferior oblique

Origin: Lateral part of annulus of Zinn

Insertion: Lateral (temporal) aspect of eyeball

Action: Abducts the eyeball – moves it away from the midline

Innervation: Abducens nerve (Cranial nerve VI)

If the abducens nerve is damaged (abducens nerves palsy/sixth nerve palsy), there is failure to abduct the affected eyeball, causing double vision in the horizontal plane.