Hemodynamic implications of the orbital muscle of Müller An anatomical study of human fetal, neonatal, and adult specimens

Abstract

The orbital muscle of Müller is considered to be rudimentary and therefore an unimportant muscle in humans. In order to determine the extension and topographic relationship of this muscle, the orbits of nine human fetuses with a crown-rump length (C-RL) ranging from 80 to 155 mm were sectioned serially, stained, and investigated under a light microscope. In addition, the orbits of three human fetuses with a C-RL ranging from 155 to 200 mm and four neonates were investigated with the aid of a binocular microscope. Transparent plastinated slices of four adult human heads sectioned sagitally, transversally, or obliquely were studied with a magnifying glass. We found the orbital muscle to be one fourth to even more than half the size of the inferior rectus muscle. The muscle of Müller was seen encircling the posterior portion of the inferior ophthalmic vein and the anterior portion of the cavernous sinus, together with a bi-located origo being attached to the sphenoid bone and orbital floor. The insertion was more tendinous and broad in the orbital floor. Between the muscle belly and plate, an anastomosing vein was found between the anterior portion of the cavernous sinus or inferior opthalmic vein and the pterygoid plexus, implying that an autonomically dictated hemodynamic regulating system still exists in humans.