THE FACIAL MUSCLES. 4^5 



Action. — The principal action of the orbicularis palpebrarum is to approximate 

 the upper and lower eyelids, closing the palpebral fissure. In addition, the attach- 

 ment of the orbital portion to the skin draws the eyebrow downward and the skin of 

 the cheek upward to form a fold around the margin of the orbit, giving increased 

 protection to the eyeball. The corrugator supercilii draws the eyebrow downward 

 and inward, producing vertical wrinkles of the integument over the glabella and giving 

 a thoughtful expression. 



The pars lacrimalis draws the tarsal plates inward and backward and so tenses 

 the internal palpebral ligament, causing it to compress the lachrymal sac. 



7. Zygomaticus Major (Figs. 499, 502). 



Attachments. — The zygomaticus major (m. zygomaticus) is a slender muscle 

 which arises above from the outer surface of the zygomatic bone, near its articulation 

 with the zygomatic process of the temporal, and passes obliquely downward and for- 

 ward towards the angle of the mouth. Its fibres interlace with those of the depressor 

 and levator anguli oris, and terminate by blending with the orbicularis oris and by 

 inserting into the subcutaneous tissue of the lips. 



Nerve-Supply. — By fibres from the zygomatic branch of the facial nerve. 



Action. — To draw upward and outward the angles of the mouth, as in smiling 

 and laughing. 



Variations. — A slender muscle is very frequently found arising from the zygomatic bone 

 anterior to the zygomaticus and passing downward to be inserted into the upper Hp. It has 

 been termed the zygomaticus 7nitior, and appears to be a separation of a portion of the zygo- 

 matic muscle. 



8. Levator Labii Superioris Al^que Nasi (Figs. 499, 501). 



Attachments. — This muscle takes its origin from the outer surface of the 

 frontal process of the maxilla, and descends along the angle which marks the junction 

 of the nose and the cheek to be inserted into the integument of the upper lip and 

 into the posterior part of the ala nasi. 



Nerve-Supply. — From the rami zygomatic! of the facial nerve. 



Action. — The principal action of this muscle is to raise the upper lip, although 

 its insertion into the ala nasi enables it to assist in the dilatation of the nostrils. 



Variations. — This muscle is subject to considerable variation in its development, and 

 frequently comes into continuity with neighboring muscles, especially with the zygomaticus 

 minor, when this is present, and with the levator labii superioris proprius. Indeed, these two 

 muscles are often associated with it to form what is termed the quadratus labii superioris, of 

 which the levator labii superioris alteque nasi forms the caput annulare, the levator labii superi- 

 oris proprius the caput infraorbitale , and the zygomaticus minor the caput zygomaticus. Since, 

 however, the levator labii superioris proprius belongs to the deep layer of the platysma muscles, 

 and therefore to a different group than the other heads of the quadratus, it seems preferable to 

 regard all the heads as distinct rnuscles. 



9. Depressor Labii Inferioris (Figs. 498, 499). 



Attachments. — The depressor of the lower lips (iti. quadratus labii inferioris) 

 arises from the body of the mandible beneath the canine and premolar teeth, its 

 origin being covered by the depressor anguli oris. It forms a thin quadrate sheet 

 which is directed upward and forward and is inserted in the skin of the lower lip, its 

 fibres mingling also with those of the orbicularis oris. 



Nerve-Supply.— From the supramandibular branch of the facial nerve. 



Action. — To draw down the lower lip. 



10. Levator Menti (Fig. 498). 



Attachments. — The levator menti (m. mentalis) arises from the body of the 

 mandible below the incisor teeth, and its fibres descend, diverging as they go, to be 

 inserted into the integument above the point of the chin. 



Nerve-Supply. — From the supramandibular branch of the facial nerve. 



