_Action._--Draws the two ears dorsad, toward the middle line.
[Illustration: FIG. 63.--MUSCLES ON THE DORSAL SURFACE OF THE HEAD.
On the right side are shown the superficial muscles; on the left side the superficial muscles have mostly been removed, exposing the deeper muscles and the bone. _a_, M. intermedius scutulorum; _b_, M. corrugator supercilii medialis; _c_, M. orbicularis oculi; _d_, M. corrugator supercilii lateralis; _e_, cranial end fibres of M. platysma; _f_, M. adductor auris superior; _g_, _g′_, M. levator auris longus (_g_, cranial portion; _g′_, caudal portion); _h_, _h′_, M. epicranius (_h_, M. occipitalis; _h′_ M. frontalis); _i_, M. transversus auriculæ; _k_, M. auricularis superior (cut on the left side); _l_, M. abductor auris brevis; _m_, M. abductor auris longus; _n_, M. temporalis; _o_, cut origin of M. frontoscutularis; _p_, _p′_, M. levator labii superioris alæque nasi (_p′_, the origin from the maxillary bone); _q_, angular head of M. quadratus labii superioris. 1, scutiform cartilage; 2, external ear; 3, bones of the skull.]
=M. corrugator supercilii medialis= (_b_).--This consists of a thin sheet of scattered fibres lying craniad of the last and intermingling with it. The fibres take origin near the middle line, pass laterad, then curve craniad, converging, to be inserted into the whole extent of the upper eyelid, especially near the caudal angle. Here the fibres unite with those of the orbicularis oculi (_c_).
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.
=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_).