Golgi tendon organs in the proximal tendon of sheep extraocular muscles

Sheep extraocular muscles were prepared for light and electron microscopy and their proximal tendons searched for Golgi tendon organs (GTO). An extensive aponeurotic lamina on the orbital surfaces contained numerous GTO 250-1350 microns in length with characteristic terminal form and relationship with collagen. They differed from usual GTO structure in containing large fluid-filled spaces dividing collagen into several well separated compartments and a muscle fiber entered and terminated in about one third of the receptors. The fibers, Felderstruktur in type, often penetrated deep within tendon organs, and in a few instances two or more fibers entered. This feature is shared by the rare GTO of monkey extraocular muscles. That the presence of GTO in the proximal tendons of extraocular muscles is previously unrecorded may be attributed to the practice of restricting attention to the long distal tendons. The possibility that receptors may be so placed in other species warrants further work especially in those purported to lack any receptor.