A. Superficial Muscles.
—The most superficial layer of muscles on the face and head is formed by differentiation of the fibres of the platysma. The muscles thus formed are not clearly distinct from each other; in this region sets of fibres differing in direction and in origin or insertion receive separate names even though the different sets of fibres are closely interwoven.
In the quadrangle on the dorsal surface of the head enclosed between the two eyes and the two ears, a thin superficial sheet of fibres is found, in which a number of different sets may be distinguished ([Fig. 63]). These have received the following names.
M. intermedius scutulorum ([Fig. 63], a).—This consists of a broad thin sheet of transverse fibres between the two external ears. The fibres are attached at either end to the scutiform cartilage (1) of the two ears, and pass without interruption across the middle line. At its cranial edge this muscle is continuous with the corrugator supercilii medialis (b); at its lateral edge with the frontoscutularis; at its caudal edge with the levator auris longus (g).
Relations.—Outer surface with the integument. Inner surface with the galea aponeurotica (to which the muscle is closely united), the epicranius muscle (h) and the temporal muscle (n).
Action.—Draws the two ears dorsad, toward the middle line.
[Fig. 63].—Muscles on the Dorsal Surface of the Head.
![[Fig. 63]](#3418956513767812439_illo097lg.jpg.id-5025637040281629436.wrap-0.html.html){kind=link}
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).