Muscles of the Head. 245 



M. cornig'ator (see Figs. 288 289). Form: flat, narrow. Position: near the root 

 of the nose, extending upward and lateralward. Origin: pars nasalis oss. frontalis. In- 

 sertien: skin of the eyebrow. Action: causes longitudinal folds at the side of the rout 

 of the nose. Innervation: n. facialis. 



M. nasalis. Form: flat, triangular. Position: lateralward from and helow the ala 

 nasi," partly cdvered by the m. ([uadratus labii superioris. 



Pars transversa. Origin: jugimi alveolare of the upper canine tooth. Insertion: to 

 the dorsum of the nose spreading out by a thin tendon to the muscle of the other side. 



Pars alar is. Origin: jugum alveolare of the upper lateral incisor tooth. Insertion: 

 lateral and lower margin of the ala nasi. 



Action: draws ala nasi downward, narrows nasal opening. Innervation: n. facialis. 



M. depressor septi. Form: flat, quadrangular. Position: below the nose, just 

 raedianward from the preceding muscle. Origin: jugum alveolare of the upper medial incisor 

 tooth. Insertion: septum nasi. Action: draws nasal septum downward, narrows nasal 

 openings. Innervation: n. facialis. 



M. risoriiis (see Fig. 286). Form: flat, triangular: very variable. Position: lateral 

 from the angle of the mouth, upon the platysma. Origin: fascia parotideoraasseterica. 

 Insertion: .unites at the angle of the mouth, or somewhat below it, with them, triangularis. 

 Action: helps to draw the angle of the muuth lateralward; causes dimple. Innervation: 

 n. facialis. 



M. zygomaticHS (see also Fig. 286). Form: oblong, flat-cylindrical. Position: 

 lateralward from and above the angle of the mouth. Origin: facies malaris oss. zygomatici. 

 Insertion: skin of the angle of the mouth ; some of the fibres go over into the 

 m. orbicularis oris. Action: draws the angle of the mouth lateralward and upward. 

 Innervation: n. facialis. 



M. caiiinus (see also Fig. 286). Form: flat, triangular. Position: in the fossa 

 canina covered by i^a m. quadratus labii superioris; comes to the surface between the latter 

 and the m. zygomaticus. Origin: fossa canina. Insertion: with converging fibres, partly 

 to the skin of the angle of the mouth: partly the fibres go over arch-like into the lower 

 lip. Action: draws the angle of the mouth upward; the muscles of the two sides together 

 lilt the lower lip and help to close the mouth. Innervation: n. facialis. 



M. triangularis (see also Figs. 286 and 297). Form : flat, triangular. Position: below 

 the angle of the mouth; covers the foramen mentale. Origin: just above the basis mandibulae 

 below the foramen mentale. Insertion: with converging fibres to the angle of the mouth and, 

 in largest part, arch-like into the upper lip. Single bundles sometimes connect the muscles of 

 the two sides below the chin ; they lie upon the platysma as the m. transversus meuti (see 

 Fig. 297). Action: draws the angle of the mouth dowmward ; the muscles of the two sides 

 together draw the uppi-r lip down and help to close the mouth. Innervation: n. facialis. 



M. quadratus labii inferioris (see also Figs. 286 and 297). Form: flat, quadrangular. 

 Position: IteLjw tlie lateral part of the mouth opening, for the most part covered bj' the 

 m. triangularis. Origin: the upper part is a direct continuation of the platysma, the lower 

 part arises from the basis mandibulae. Insertion: skin of lower lip. Action: draws the 

 lower lip lateralward and downward. Innervation: n. facialis. 



M. incisiviis labii superioris (see also Fig. 293). Form: flat, triangular, narrow. 

 Position: above the angle of the mouth, covered by the m. quadratus labii superioris, at the 

 upper margin of the ni. orbicularis oris. Origin: jugum alveolare of the upper canine tooth. 

 Insertion: arch-like to the angle of the mouth, interwoven there with the other muscles. 

 Action: draws the angle of the mouth median ward and upward. Innervation: n. facialis. 



M. incisivus labii inferioris (see also Fig. 293). Form: flat, quadrangular, narrow. 

 Position: below the angle of the mouth, covered by the m. quadratus labii inferioris, at the 

 lower margm of the m. orbicularis oris. Origin: jugum alveolare of the lower lateral incisor 

 tooth. Insertion: to the lower margm of the m. orbicularis oris, iirterweaving with it. Action: 

 draws the angle of the m.outh medianward. Innervation: n. facialis. 



M. orbicularis oris, a muscle-plate situated in the lips which owes its formation to 

 the fact that the muscles going to the mouth opening, at the angles of the mouth, partly 

 radiate out into the upper or lower lip. The fibres run in the lips for the most part trans- 

 versely, at the angles of the mouth also arch-like between the two lips and are attached in 

 part to the external skin. In this way a sort of ring muscle is formed. Action: if it con- 

 tracts alone it closes the mouth and points it. Innervation: n. facialis. 



M. mentalis. Form: thick, cyUndrical, short. Position: on the chin. Origin: 

 jugum alveolare of the lower medial incisor tooth. Insertion: obhquely downward into the 

 skin of the chin. Action: lifts the skin of the chin and wrinkles it. Innervation: n. facialis. 



