The structure indicated is the orbicularis oculi muscle of the face.
The orbicularis oculi muscle is one of the muscles of facial expression belonging to the orbital group. The muscles of facial expression can be organised into functional groups to provide a more structured approach to understanding the muscles. The functional groups include the following:
- Orbital group
- Nasal group
- Oral group
The orbicularis oculi muscle is the principle muscle of the orbital group of facial muscles and consists itself of two parts:
- Palpebral part
- Orbital part
There is an additional muscle in the orbital group – the corrugator supercilli which is a small, narrow muscle located medially in the orbit just below the frontalis muscle which contracts to bring the eyebrow inferomedially.
The orbicularis oculi muscle acts as a sphincter surrounding the orbital orifice. The palpebral part is in the eyelids, whereas the orbital part forms the outer part of the muscle circling around the orbital orifice. The word “palpebral” relates to the latin word for “eyelid”.
Learn more about the muscles of facial expression in this tutorial