Part 22

Relations.--Outer surface with the abductor longus (m), a small strand of the platysma and the concha. Inner surface with the temporal muscle (n).

Action.--Pulls the concha caudad.

=M. epicranius= (or occipitofrontalis) (Fig. 63, h and h′).

Origin on the sagittal crest or suture, just craniad of the origin of the levator longus auris, to the inner surface of which this muscle is closely united. From the origin the fibres pass craniad forming a band (h) about 8 or 10 millimeters in width, the two muscles lying close to one another and partly united in the middle line. About two centimeters craniad of their origin the fibres of both muscles end in a tendinous sheet, the =galea aponeurotica=, which covers the surface of the skull in the region between the ears and eyes, and is formed by the inner surface of the intermedius scutulorum (a) and other muscles of this region. The galea aponeurotica passes craniad onto the surface of the nose, where it gives origin again to a thin sheet of muscle-fibres (h′) which are inserted into the integument near the cranial ends of the nasal bones.

M. epicranius is thus formed of two muscular portions (h and h′), connected by a long tendinous sheet. The caudal portion is frequently distinguished as the occipital muscle (=M. occipitalis=, h), the cranial portion, on the nose, as the =frontal= muscle (=M. frontalis=, h′).

Relations.--Outer surface of the occipitalis (h) with the intermedius scutulorum (a), the levator auris longus (g), and the integument; inner surface with the auricularis superior (h), the abductor auris longus, and the bone. Outer surface of the frontalis (h′) with the integument; inner surface with the bones of the skull.

Action.--Moves the integument of the dorsal surface of the head and of the nose.

Ventrad of the external ear the following three differentiated portions of the platysma may be distinguished.

=M. zygomaticus= (major) (Fig. 64, d).--A slender band connecting the angle of the mouth with the scutiform cartilage of the ear.

a, a′, a″, M. platysma; b, M. depressor conchæ; c, M. submentalis; d, M. zygomaticus (b, c, and d lie beneath the platysma and are seen through it); e, M. zygomaticus minor; f′, M. caninus; f, g, parts of M. quadratus labii superioris (f, angular head; g, M. levator labii superioris alæque nasi); h, M. myrtiformis; i, M. orbicularis oris; j, M. corrugator supercilii medialis; k, M. corrugator supercilii lateralis; l, M. adductor auris superior; m, M. helicis; n, M. antitragicus; o, M. adductor auris inferior; p, M. conchæus externus; q, M. abductor auris longus; r, parts of M. auricularis externus; s, M. orbicularis oculi.]

At the angle of the mouth the fibres arise from among those of the orbicularis oris (i), from both the upper and the lower lip. They pass thence dorsocaudad across the zygomatic arch as a band 8 or 10 millimeters wide which is attached to a tendinous aponeurosis lying just craniad of the external opening of the ear. To this aponeurosis are attached also, wholly or partly, the corrugator supercilii lateralis (k) and the submentalis (c). The aponeurosis is united with the caudoventral angle of the scutiform cartilage and with the ventral edge of the cranial margin of the auricular cartilage.

This muscle is united at its cranial end with the orbicularis oris (i); throughout its length more or less with the platysma (a, a′); at its caudodorsal end with the corrugator supercilii lateralis (k) on its medial side, and with the submentalis (c) on its lateral side.

Relations.--Outer surface with the integument and the platysma (a′). Inner surface with the masseter, temporal, frontoscutularis, and adductor auris inferior (o).

Action.--Draws the angle of the mouth dorsocaudad; the external ear ventrocraniad.

=M. submentalis= (Fig. 64, c).--A flat band, similar to the last, and closely connected for some distance to its caudal border.

It arises as scattered fibres near the ventral middle line at about the level of the larynx, the fibres of the opposite muscles crossing the middle line and intermingling. The fibres pass dorsad, converging so as to form a narrower band, which unites dorsad with the zygomaticus (d), to be inserted with it into the tendinous aponeurosis above described.

Relations.--Outer surface with the integument and platysma (a′). Inner surface with the muscles of the hyoid, the digastricus, the parotid gland, the masseter, the zygomatic arch and the temporal muscle.

Action.--Draws the external ear ventrad.

=M. depressor conchæ= (Fig. 64, b).--A thin band of fibres, caudad of the last and parallel with it. The muscle arises as scattered fibres on the ventral surface of the neck, one or two centimeters craniad of the manubrium, the fibres of the muscles of opposite sides crossing the middle line and interdigitating. They pass dorsad, gathering together to form a narrow band which is inserted into the summit of the antitragus.

Relations.--Outer surface with the skin at the ventral end, and with the platysma (a′) further dorsad. Inner surface with the deep muscles of the neck and with the parotid gland.

Action.--Draws the external ear ventrad.

Lying deeper than the muscles thus far described, but closely connected with a number of them, are the following:

=M. frontoscutularis.=

Origin (Fig. 63, o) on the frontal bone, along the supraorbital margin, from the craniomedial angle of the eye caudad to the zygomatic process of the frontal.

The fibres form a large muscle which passes dorsocaudad to the scutiform cartilage and is mostly attached along its ventrolateral border. Some of the outer fibres, however, pass distad of the scutiform cartilage toward the cartilage of the ear, thus joining the adductor auris superior (f).

The outer surface of this muscle is closely connected with fibres of the intermedius scutulorum (a), the corrugatores supercilii medialis (b) and lateralis (d), and the frontoauricularis, when this exists. The outer surface is covered near the origin by the orbicularis oculi (c), farther dorsad by the muscles just mentioned and the integument. The inner surface is in relation with the frontal bone and the adductor auris inferior (Fig. 64, o).

Action.--Pulls the ear craniad.

=M. adductor auris inferior.= (Fig. 64, o.) (Part of the auricularis anterior of man.)--A small muscle lying beneath the frontoscutularis.