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. 
carried to the fullest extent, results in eversion of the lip. 
lip is drawn upward and to the side of 
the muscle acting. 
Structure.—The muscle has ashort, 
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.! 
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—F acial nerve. 
4. Zygomaticus.—This very thin 
muscle hes 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. 
Nerve-supply.—F acial 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. 
This action, if 
In unilateral action the 
Fic. 262—Mutsctes or Heap oF Horse; Dorsat View. 
THe M. curaneus 1s REMOVED. 
a, Levator labii super 
tendon of a with opposite muscle; 6b, levator nasolabialis; 
f, dilatator naris lateralis; g, zygomaticus; lI, 
nasi; m, parotido-auricularis; o’’, scutulo-auricularis super- 
ficialis superior; p, interscutularis; p’, fronto-scutularis, 
pars temporalis; r, cervico-auricularis superficialis; u, 
corrugator supercilii; z, transversus na 2, posterior, 
3, anterior, border of external ear; 8, scutiform cartilage; 
9, zygomatic arch; 10, supraorbital depression; 35, medial 
wing of nostril, containing lamina of alar cartilage; 39, 
facial vein. (After Ellenberger-Baum, Anat. fir Kistler.) 
proprius; a’, common 
lateralis 
Origin.—The alveolar border of the mandible from the second incisor to a 
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 
