
The infraorbital nerve is a branch of the maxillary branch.Illustration of lips from Gray's Anatomy showing the inferior and superior labial arteries, the glands of the lips, and the nerves of the right side seen from the posterior surface after removal of the mucous membrane The Frenulum Labii Superioris is the frenulum of the upper lip. The Frenulum Labii Inferioris is the frenulum of the lower lip. The mucous membrane is represented by a large area in the sensory cortex, and is therefore highly sensitive.
SEXUALLY LIPS QUIVER MEANING SKIN
The skin of the lips is stratified squamous epithelium. Thinning of the vermilion of the upper lip and flattening of the philtrum are two of the facial characteristics of fetal alcohol syndrome, a lifelong disability caused by the mother's consumption of alcohol during pregnancy. It is raised by the levator labii superioris and is connected to the lower lip by the thin lining of the lip itself. Its upper half is of usual skin color and has a depression at its center, directly under the nasal septum, called the philtrum, which is Latin for "lower nose", while its lower half is a markedly different, red-colored skin tone more similar to the color of the inside of the mouth, and the term vermillion refers to the colored portion of either the upper or lower lip. The upper lip covers the anterior surface of the body of the maxilla. It is lowered by the depressor labii inferioris muscle and the orbicularis oris borders it inferiorly. The lower lip covers the anterior body of the mandible. The lower lip is formed from the mandibular prominence, a branch of the first pharyngeal arch. For these reasons, the lips dry out faster and become chapped more easily. Therefore, it does not have the usual protection layer of sweat and body oils which keep the skin smooth, inhibit pathogens, and regulate warmth. The lip skin is not hairy and does not have sweat glands. The skin of the lip forms the border between the exterior skin of the face, and the interior mucous membrane of the inside of the mouth. With darker skin color this effect is less prominent, as in this case the skin of the lips contains more melanin and thus is visually darker. Because of this, the blood vessels appear through the skin of the lips, which leads to their notable red coloring.

With light skin color, the lip skin contains fewer melanocytes (cells which produce melanin pigment, which give skin its color). The skin of the lip, with three to five cellular layers, is very thin compared to typical face skin, which has up to 16 layers.
