The Procerus (Pyramidalis nasi) is a small pyramidal slip arising by tendinous fibers from the fascia covering the lower part of the nasal bone and upper part of the lateral nasal cartilage; it is inserted into the skin over the lower part of the forehead between the two eyebrows, its fibers decussating with those of the Frontalis.
The Nasalis (Compressor naris) consists of two parts, transverse and alar. The transverse partarises from the maxilla, above and lateral to the incisive fossa; its fibers proceed upward and medialward, expanding into a thin aponeurosis which is continuous on the bridge of the nose with that of the muscle of the opposite side, and with the aponeurosis of the Procerus. The alar part is attached by one end to the greater alar cartilage, and by the other to the integument at the point of the nose.
The Depressor septi (Depressor al nasi) arises from the incisive fossa of the maxilla; its fibers ascend to be inserted into the septum and back part of the ala of the nose. It lies between the mucous membrane and muscular structure of the lip.
The Dilatator naris posterior is placed partly beneath the Quadratus labii superioris. It arises from the margin of the nasal notch of the maxilla, and from the lesser alar cartilages, and is inserted into the skin near the margin of the nostril.
Actions.The Procerus draws down the medial angle of the eyebrows and produces transverse wrinkles over the bridge of the nose. The two Dilatatores enlarge the aperture of the nares. Their action in ordinary breathing is to resist the tendency of the nostrils to close from atmospheric pressure, but in difficult breathing, as well as in some emotions, such as anger, they contract strongly. The Depressor septi is a direct antagonist of the other muscles of the nose, drawing the ala of the nose downward, and thereby constricting the aperture of the nares. The Nasalis depresses the cartilaginous part of the nose and draws the ala toward the septum.