Recent studies have promoted the concept that rectus muscles pass through connective tissue pulleys located near the equator of the eye and act, in effect, as the muscle origins. Orbital muscle fibres (facing bone) terminate in pulleys, permitting adjustment of their position independent of the global fibres responsible for rotating the eye.The structure of pulleys (or muscle sleeves) and the passage taken by their muscle fibre insertions are unclear, and a detailed description is presented here together with a review of the active pulley hypothesis. Segments including the full width of single muscles were removed from the full orbital contents of dissection room cadavers and fresh perfusion-fixed rhesus and cynomolgus monkeys and prepared for light microscopy. Thin longitudinal sections were cut as facets from resin-embedded tissue blocks and montages assembled. Interrupted serial sections of selected regions of both species and ultrathin sections of monkey material were prepared for light and electron microscopy, respectively. Slender tendons leave the orbital surface of rectus muscles at intervals, aggregating and entering sleeves in humans and monkey; less frequently, tendons pass from the global surface to sleeves or insert directly in the posterior fascia bulbi. The orbital sides of sleeve rings are continuous with the fascial canopy of the globe and are 5 -6 times as thick as the global sides; sleeve structure differs in the four recti. Medial rectus sleeves are the thickest, and contain smooth muscle, whereas little or none is present in the other rectus sleeves. Superior rectus sleeves are variable in structure and relatively insubstantial. A narrow interval separates muscles from the surrounding connective tissue equatorially in some preparations, consistent with a capacity to slide, but the tissues are contiguous in others, especially in monkey material. The structural organization of sleeves and their tendons, together with other presented factors, is inconsistent with a facility for the separate adjustment of sleeve position.The results favour the theory that sleeve tendons have just one role, to counter the viscoelastic resistance of global fascia -ocular and sleeve muscle fibres acting in unison. Whether the fragile sleeve structure can meet the physical demands of pulleys is questionable; but otherwise the veracity of the pulley hypothesis cannot be assessed from the structural relations of muscles and fascia bulbi reported.

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In order to study the three-dimensional topography of the intra-orbital autonomic nerve plexuses and the input for these systems, human fetuses and adult rhesus monkeys were investigated. Specimens of the orbits were processed according to the histochemical acetylcholinesterase methods for staining of peripheral nerves. The nerve fibers enter the orbit along the following pathways: 1. bundles of nerve fibers from the pterygopalatine ganglion (mainly parasympathetic) by penetrating the orbital muscle (Müller); 2. perivascularly along the ophthalmic artery (sympathetic). In the orbit the nerve fibers intermingle. The pathways of the nerve fibers from this interwoven nerve plexus towards the target organs are: 1. perivascularly along branches of the ophthalmic artery; 2. perineurally along and in the branches of the ophthalmic and maxillary nerves; 3. independently of blood vessels and cranial nerve branches in Tenon's capsule. Moreover, bundles of nerve fibers from the ciliary ganglion contribute to the innervation of extraocular structures, e.g. the eyelids. It can be concluded that, as far as the autonomic innervation of the orbit is concerned, the monkey is a good animal model for neuroanatomical studies.

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