Part 21

=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.

Action.--Pulls the angle of the eye caudad; at the same time pulls the external ear craniad.

=M. frontoauricularis.=--A few of the fibres which are attached along the upper eyelid sometimes pass dorsocaudad, mingled with fibres of the corrugatores supercilii medialis and lateralis and the frontoscutularis, to the craniomedial angle of the auricular cartilage, where they unite with the fibres of the adductor auris superior. These fibres are sometimes distinguished as the =frontoauricularis= muscle.

=M. levator auris longus= (Fig. 63, g and g′). (Part of the auricularis posterior of man.)--This lies on the caudal half of the dorsal surface of the head, forming a laterocaudal continuation of the intermedius scutulorum (a).

Origin from the middle line of the neck dorsad of the atlas, and from the sagittal crest for about one centimeter craniad of the external occipital tubercle. The fibres form a broad thin sheet which passes craniolaterad as far as the caudal end of the scutiform cartilage (1). Here the muscle divides; the major portion is attached to the scutiform cartilage (1), its fibres intermingling with those of the intermedius scutulorum (a). The caudal portion of the muscle (g′) passes onto the surface of the auricle, extending one or two centimeters distad; here it is inserted on an oblique line which lies directly craniad of the insertion of the transversus auriculæ (i).

The caudal portion of this muscle (g′) having origin above the atlas and insertion on the auricle, is sometimes considered a separate muscle, the supercervicoauricular or cervicoauricular. The cranial portion (g) with origin on the sagittal crest and insertion on the scutiform cartilage might be distinguished as the occipitoscutularis.

The levator auris longus is continuous at its cranial end medially with M. epicranius (h); laterally with M. intermedius scutulorum (a).

Relations.--Outer surface with the integument. Inner surface with the temporal muscle (n), the auricularis superior (k), the abductor longus auris (m), a narrow strand of the platysma, and the clavotrapezius.

Action.--Pulls the external ear dorsocaudad.

The four following muscles lie partly or entirely beneath those already described; they are doubtless formed as differentiations of the inner layers of the platysma.

=M. auricularis superior= (or attollens auris) (Fig. 63, k).--This muscle forms a band about one centimeter broad lying just beneath the levator longus (g).

Origin on the sagittal crest for about one centimeter craniad of the interparietal bone. The muscle passes laterad onto the surface of the auricle and is inserted into the auricular cartilage a little caudad of the middle of its convex surface. At its lateral end the cranial margin is closely united to the under surface of the levator auris longus (g).

Relations.--Outer surface at the medial end with the epicranius (h), the abductor auris longus (m), and levator auris longus (g); at the lateral end with the skin. Inner surface with the temporal muscle (n) and the auricular cartilage.

Action.--Pulls the external ear dorsad.

=M. abductor auris longus= (Fig. 63, m; Fig. 64, q). (Part of the auricularis posterior of man.)

Origin on the sagittal crest dorsad of the interparietal bone, caudad of that of the auricularis superior (k), which it partly covers.

The muscle passes laterad as a flat band 8 to 10 millimeters wide over the caudal surface of the concha of the ear, and is inserted (Fig. 64, q) on the lateral surface of the eminentia conchæ, caudad of the antitragus.

Relations.--Outer surface with the levator auris longus (g) and the integument. Inner surface with the auricularis superior (k), the abductor auris brevis (l), and the concha.

Action.--Pulls the external ear caudad.

=M. abductor auris brevis= (Fig. 63, l).

Origin by a tendon from the lambdoidal crest for one or two centimeters laterad of the middle.

The muscle passes lateroventrad lying beneath the abductor longus (m) as a flat band 6 to 8 millimeters wide which is inserted into the medial surface of the most proximal portion of the concha, just distad of its junction with the cartilaginous auditory meatus.