THE FACIAL MUSCLES. 487 



Variations. — Fibres from the nasalis sometimes pass upward upon the nasal bones and 

 may enter into the formation of the pyramidalis nasi ( page 482). Frequently the pars alaris and 

 pars transversa are recognized as distinct muscles, the former being termed the depressor alee 

 nasi or myrtiformis, while the latter is named the compressor iiariimi. Uncertain and at best 

 feeble muscular slips on the outer margin of the nostrils are sometimes described as distinct 

 muscles, the dilatores naris anterior et posterior. 



3. Levator Labii Superioris (Fig. 499). 



Attachments. — The elevator of the upper lip (m. levator labii superioris pro- 

 prius) arises above from the infraorbital margin of the maxilla and extends almost 

 vertically downward over the infraorbital vessels and nerve to join with the orbicu- 

 laris oris and also to be inserted into the skin of the upper lip between the insertions 

 of the levator labii superioris alaeque nasi and the levator anguli oris. 



Nerve-Supply. — From the zygomatic branches of the facial nerve. 



Action. — To raise the upper lip. Acting in conjunction with the levator labii 

 superioris alaeque nasi, it plays an important part in the expression of grief. 



4. Levator Anguli Oris (Figs. 499, 502). 



Attachments. — The elevator of the angle of the mouth (m. caninus) arises from 

 the canine fossa of the maxilla by a rather broad origin, from which its fibres con- 

 verge to be inserted into the skin at the angle of the mouth, partly mingling with the 

 fibres of the depressor anguli oris. 



Nerve-Supply. — From the zygomatic branches of the facial nerve. 



Action. — To raise the ang^le of the mouth. 



'&' 



5. RisoRius (Fig. 499). 



Attachments. — The risorius is a triangular sheet of muscle which arises from 

 the outer surface of the parotido-masseteric fascia and from the integument of the 

 cheek and passes forward towards the angle of the mouth, where it unites with the 

 depressor anguli and orbicularis oris. 



Nerve-Supply. — From the rami buccales of the facial nerve. 



Action. — To draw the angle of the mouth outward. Its contraction imparts 

 a tense and strained expression to the face which is termed the risus sardonicus. 



Variation. — The risorius is frequently absent, and may be represented only by some 

 scattered muscular bands. Its intimate association with the depressor anguli oris indicates its 

 derivation from that muscle. 



6. Depressor Anguli Oris (Figs. 498, 499). 



Attachments. — The depressor of the angle of the mouth (m. triangularis) 

 takes its origin from the outer surface of the body of the mandible and from the skin 

 and passes upward to the angle of the mouth, where its fibres are inserted into the 

 skin and also mingle with those of the caninus, risorius, and orbicularis oris. 



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



Action. — To draw the angle of the mouth downward and slightly outward, 

 giving an expression of sorrow. 



Variations. — A bundle of fibres not infrequently, arises from the anterior border of the 

 depressor anguli oris near its origin and passes obliquely downward and inward towards the 

 median line beneath the chin, either losing itself in the superficial fascia of that region or uniting 

 with its fellow of the opposite side. This slip has been regarded as a distinct' muscle and 

 termed the transversus me?iti. It seems exceedingly probable that both this bundle and the 

 risorius are derivatives of the depressor, and this muscle, notwithstanding its position super- 

 ficial to both the depressor labii inferioris and the platysma, is really a portion of the deeper 

 layer of the platysma musculature, its present position having been acquired by a migration from 

 the region of the upper lip. 



