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

The orbital muscle of Muller is considered to be rudimentary and therefore an unimportant muscle in humans. In order to determine the extension and to pographic relationship of this muscle, the orbits of nine human fetuses wit h a crown-rump length (C-RL) ranging from 80 to 155 mm were sectioned seria lly, stained, and investigated under a light microscope. In addition, the o rbits of three human fetuses with a C-RL ranging from 155 to 200 mm and fou r neonates were investigated with the aid of a binocular microscope. Transp arent plastinated slices of four adult human heads sectioned sagitally, tra nsversally, 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 inf erior rectus muscle. The muscle of Muller was seen encircling the posterior portion of the inferior ophthalmic vein and the anterior portion of the ca vernous sinus, together with a bi-located origo being attached to the sphen oid bone and orbital floor. The insertion was more tendinous and broad in t he orbital floor. Between the muscle belly and plate, an anastomosing vein was found between the anterior portion of the cavernous sinus or inferior o pthalmic vein and the pterygoid plexus, implying that an autonomically dict ated hemodynamic regulating system still exists in humans.