Image by/from Uwe Gille
The levator labii superioris (or quadratus labii superioris) is a skeletal muscle of the body utilized in facial expression. It’s a wide sheet, the origin of which stretches from the side of the nose to the zygomatic bone.
Its medial fibers make up the angular head (likewise called the levator labii superioris alaeque nasi muscle,) which develops by a pointed extremity from the superior aspect of the frontal process of the maxilla and passing obliquely down and lateralward splits into 2 slips.
Among these is inserted into the greater alar cartilage and skin of the nose; the other is stretched out into the lateral aspect of the top lip, mixing with the infraorbital head and with the orbicularis oris.
The intermediate part or infraorbital head emerges from the lower margin of the orbit immediately just above the infraorbital foramen, a few of its fibers being connected to the maxilla, others to the zygomatic bone.
Its fibers assemble, to be inserted into the muscular portion of the top lip in between the angular head and the levator anguli oris.
The lateral fibers, composing the zygomatic head (likewise called the zygomaticus minor muscle,) emerge from the malar surface of the zygomatic bone immediately behind the zygomaticomaxillary suture and pass down and medialward to the top lip.
Its primary action is to raise top lip.