MUSCLES OF THE LIPS AND CHEEKS 



215 



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 com- 

 missure with the orbicularis and buc- 

 cinator. 



Relations. — Superficially, the skin, 

 fascia, and lateral dilator (in part); 

 deeply, the levator labii superioris pro- 

 prius, lateral dilator (in part), buccin- 

 ator, branches of the facial vessels and 

 nerve, and the infraorbital artery and 

 nerve. 



Blood-supply. — Facial and palato- 

 labial arteries. 



Nerve-supply. — Facial nerve. 



3. Levator labii superioris pro- 

 prius. — This lies on the dorso-lateral 

 aspect of the face, i)artly 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 be- 

 comes narrower and thicker, then 

 tapers over the false nostril, to termin- 

 ate in a tendon. The tendons of the 

 two muscles unite over the alar car- 

 tilages of the nostrils, forming an ex- 

 pansion which spreads out in the sub- 

 stance of the upper lip. 



Relations. — Superficially, the skin, 

 the levator nasolabialis, and the angu- 

 lar 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. 



Fig. 173. — Muscles of Head of Horse, Dorsal View. 

 The Panniculus is Removed. 

 a. Levator labii superioris proprius; a', common 

 ternlon of a with opposite muscle; b, levator nasolabialis; 

 /, dilatator naris lateralis; g, zygomaticus; I, dilatator 

 naris superior; n, parotido-auricularis; o" , scutulo-auricu- 

 laris superficialis superior; p, interscutularis; p', fronto- 

 scutularis, pars temporalis; )■, cervico-auricularis superfici- 

 alis; u, corrugator supercilii; r, transversus nasi; 2, poste- 

 rior, 3, anterior, border of external ear; S, scutiform carti- 

 lage; 9, zygomatic arch; 10, supraorljital depression; 35, 

 inner wing of nostril, containing lamina of alar cartilage; 

 39, facial vein. (After EIlenberger-Baum, Anat. fur 

 Kunstler.) 



