Motor and sensory innervation of extraocular eye muscles.

Eye muscles are unusual in several ways; one is that they have up to three different layers-the inner global layer, the outer orbital layer, and in some species an external marginal layer has been described. In sheep this is called the "peripheral patch layer." Three different types of proprioceptors are found in eye muscles-muscle spindles, Golgi tendon organs, and palisade endings. A survey of the organization of their location leads us to the hypothesis that each receptor is confined to a separate layer of the eye muscle. The palisade endings are associated with the global layer, the muscle spindles lie predominantly in the orbital layer, and the Golgi tendon organs are found only in the peripheral patch layer. This well-organized scheme may help us to understand the proprioceptive system in eye muscles.