MUSCLES OF THE LIPS AND CHEEKS 



257 



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



Action.— Acting with its fellow, to elevate the upper lip. This action if 

 earned to the fullest extent, results in eversion of the lip. 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 nasal 

 diverticulum, 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.i 



Relations. — Superficially, the skin, 

 the levator nasolabialis, and the angu- 

 lar vessels of the eye; deeply, the later- 

 alis nasi, the transversus nasi, 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 mih 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. 



Nerve-supply. — Facial nerve. 



5. Incisivus superior. — This lies 

 under the mucous membrane of the 

 upper lip. 



Origin. — The alveolar border of 

 the premaxilla from the second incisor 

 to the first cheek tooth. 



Insertion. — The upper lip. 



Action. — To depress the upper 

 lip. 



6. Incisivus inferior. — This is ar- 

 ranged in the lower lip like the pre- 

 ceding muscle in the upper one. 



Origin. — The alveolar border of the 

 point near the first cheek tooth. 



1 In rare cases a branch is given off from the ventral border of the muscle. It passes forward 

 and ends in the subcutaneous tissue at the posterior end of the diverticulum nasi. 

 17 



Fig. 



262. — Muscles of Head of Horse; Dorsal A'iew. 



The M. cutaneus is Removed. 

 a. Levator labii superioris proprius; a\ common 

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

 /, dilatator naris lateralis; p, zygomaticus; /, lateralis 

 nasi; n, parotido-auricularis; o", scutulo-auricularis super- 

 ficialis superior; p, interscutularis ; j>', fronto-scutularis, 

 pars temporalis; r, cervico-auricularis superficialis; u, 

 corrugator supercilii; x, transversus nasi; J, posterior, 

 S, anterior, border of external ear; S, scutiform cartilage; 

 5, zygomatic arch; 10, supraorbital depression; 3o, medial 

 wing of nostril, containing lamina of alar cartilage; 39, 

 facial vein. (After Ellenberger-Baum, Anat. fiir Kiinstler.) 



mandible from the second incisor to a 



