This muscle is continuous caudad with the intermedius scutulorum (a), craniad with the orbicularis oculi (c); laterad with the corrugator supercilii lateralis (d). Toward the medial side the fibres lose themselves in a tendinous sheet that joins the galea aponeurotica.
Relations.—Outer surface with the integument. Inner surface with the frontoscutularis and the skull.
Action.—Raises the upper eyelid.
M. orbicularis oculi ([Fig. 63], c; [Fig. 64], s).—This consists of two thin bands of muscle-fibres which lie one in either eyelid parallel to its border and unite at the angle of the eye.
Origin by short tendon-fibres from a tubercle on the surface of the frontal process of the maxillary bone just dorsad of the orbital end of the lachrymal canal and between the two parts of the quadratus labii superioris ([Fig. 63], p and q).
The muscle splits into two parts which pass into the two eyelids. At the outer angle of the eye the two bands unite by the intervention of tendon-fibres between the muscle-fibre bundles of the two.
Relations.—Outer surface with the integument. Inner surface with the inner membrane of the eyelid.
Action.—Closes the eye.
M. corrugator supercilii lateralis ([Fig. 63], d; [Fig. 64], k).—This consists of a number of scattered fibres which arise from among the fibres of the frontoscutularis, and from the tendon lying just craniad of the external opening of the ear, to which are united also parts of the zygomaticus ([Fig. 64], d) and submentalis ([Fig. 64], c). The fibres pass craniad, converging so as to form a narrow band which is inserted at the caudolateral angle of the eye, where it unites with the orbicularis oculi ([Fig. 64], s). This muscle is continuous on the medial side with the corrugator supercilii medialis ([Fig. 64], j) and the frontoauricularis, on the lateral side with the platysma.
Relations.—Outer surface with the integument. Inner surface with the frontal bone and the frontoscutularis.