Part 56

Nerve-supply.—Facial nerve.

FIG. 172.—MUSCLES OF HEAD OF HORSE, LATERAL VIEW. THE PANNICULUS IS REMOVED.

a, Levator labii superioris proprius; b, levator nasolabialis; c, mastoido-humeralis; d, sterno-cephalicus; d′, tendon of d; e, omo-hyoideus; f, dilatator naris lateralis; g, zygomaticus; h, buccinator; i, depressor labii inferioris; k, orbicularis oris; l, dilatator naris superior; m, masseter; n, parotido-auricularis; o, zygomatico-auricularis; p, interscutularis; p′, fronto-scutularis, pars temporalis; q, cervico-auricularis profundus major; r, cervico-auricularis superficialis; s, obliquus capitis anterior; t, splenius; v, stylo-maxillaris; y, mastoid tendon of mastoido-humeralis; 2, posterior, 3, anterior, border of external ear; 8, scutiform cartilage; 9, zygomatic arch; 10, depression behind supraorbital process; 18, temporo-mandibular articulation; 27, facial crest; 30′, angle of jaw; 37, external maxillary vein; 38, jugular vein; 39, facial vein; 40, parotid duct; 41, transverse facial vein; 42, masseteric vein; 43, facial nerve; 44, parotid gland; 45, chin; x, wing of atlas. (After Ellenberger-Baum, Anat. für Künstler.) ]

2. =Levator nasolabialis= (Levator labii superioris alæque nasi).—This thin muscle lies directly under the skin, and chiefly on the lateral surface of the nasal region.

Origin.—The frontal and nasal bones.

Insertion.—(1) The upper lip and the outer wing of the nostril; (2) the commissure of the lips.

Action.—(1) To elevate the upper lip and the commissure; (2) to dilate the nostril.

Structure.—The muscle arises by a thin aponeurosis. The belly is also thin, and divides into two branches, between which the lateral dilator of the nostril passes. The dorsal branch reaches the nostril and upper lip, blending with the lateral dilator; the ventral one is much smaller, and blends at the labial commissure with the orbicularis and buccinator.

Relations.—Superficially, the skin, fascia, and lateral dilator (in part); deeply, the levator labii superioris proprius, lateral dilator (in part), buccinator, branches of the facial vessels and nerve, and the infraorbital artery and nerve.

Blood-supply.—Facial and palato-labial arteries.

Nerve-supply.—Facial nerve.

FIG. 173.—MUSCLES OF HEAD OF HORSE, DORSAL VIEW. THE PANNICULUS IS REMOVED.

a, Levator labii superioris proprius; a′, common tendon of a with opposite muscle; b, levator nasolabialis; f, dilatator naris lateralis; g, zygomaticus; l, dilatator naris superior; n, parotido-auricularis; o″, scutulo-auricularis superficialis superior; p, interscutularis; p′, fronto-scutularis, pars temporalis; r, cervico-auricularis superficialis; u, corrugator supercilii; x, transversus nasi; 2, posterior, 3, anterior, border of external ear; 8, scutiform cartilage; 9, zygomatic arch; 10, supraorbital depression; 35, inner wing of nostril, containing lamina of alar cartilage; 39, facial vein. (After Ellenberger-Baum, Anat. für Künstler.) ]

3. =Levator labii superioris proprius.=—This lies on the dorso-lateral aspect of the face, partly covered by the preceding muscle.

Origin.—The lacrimal, malar, and maxillary bones at their junction.

Insertion.—The upper lip, by a common tendon, with its fellow.

Action.—Acting with its fellow, to elevate the upper lip. This action, if carried to the fullest extent, results in eversion. In unilateral action the lip is drawn upward and to the side of the muscle acting.

Structure.—The muscle has a short, thin tendon of origin. The belly is at first flattened, but becomes narrower and thicker, then tapers over the false nostril, to terminate in a tendon. The tendons of the two muscles unite over the alar cartilages of the nostrils, forming an expansion which spreads out in the substance of the upper lip.

Relations.—Superficially, the skin, the levator nasolabialis, and the angular vessels of the eye; deeply, the superior and transverse dilators of the nostril and the infraorbital artery and nerve.

Blood-supply.—Facial artery.

Nerve-supply.—Facial nerve.

4. =Zygomaticus.=—This very thin muscle lies immediately under the skin of the cheek.

Origin.—The fascia covering the masseter muscle below the facial crest.

Insertion.—The commissure of the lips, blending with the buccinator.

Action.—To retract and raise the angle of the mouth.

Structure.—Fleshy, with a thin aponeurotic origin.

Relations.—Superficially, the skin; deeply, the buccinator.

Blood-supply.—Facial artery.