486 



HUMAN ANATOMY. 



Action. — To draw upward the skin of the chin, thereby causing protrusion of 

 the lower Hp, as in pouting. When its action is combined with contraction of the 

 depressors of the angles of the mouth, it gives an expression of haughtiness or con- 

 tempt, and has thence been termed the m. siiperbus. When slightly contracted, it 

 gives an expression of firmness or decision. 



Belonging to the superficial layer of the platysma musculature are a number pf 

 additional more or less rudimentary muscles attached at both extremities to various 

 parts of the cartilage of the concha. These muscles will be considered in connection 

 with the description of the ear (page 1499). 



{b) THE MUSCLES OF THE DEEP LAYER. 

 I. Orbicularis Oris (Figs. 499, 501, 503). 



Attachments. — The orbicularis oris is a rather strong elliptical muscle whose 

 fibres occupy the thickness of both the upper and lower lips between the skin and 

 the mucous membrane of the mouth. For the most part the fibres composing the 

 muscle are forward prolongations of the buccinator, but mingled with these there are 

 fibres from all the muscles which are inserted in the vicinity of the mouth, such as 

 the zygomaticus, levator anguli oris, levator labii superioris, depressor anguli oris, 

 depressor labii inferioris, and risorius. 



It possesses, however, some slight attachment to skeletal structures by three 

 groups of fibres which have frequently been regarded as distinct muscles. These 

 groups are : ( i ) the incisivi labii superioris, a series of bundles of fibres which arise 

 from the incisive fossae of the maxillae and pass downward and outward to mingle 

 with the other fibres of the orbicularis at the angles of the mouth ; (2) the incisivi 

 labii inferioris, which arise from the alveolar border of the mandible beneath the 

 canine teeth and unite with the orbicularis at the angles of the mouth ; and (3) the 

 depressor septi, composed of the uppermost fibres of the orbicularis, which bend up- 

 ward from either side in the median line and are inserted into the margin of the septal 

 cartilage of the nose. 



Nerve-Supply. — From the rami buccales and supramandibular branch of the 



facial nerve. 



Action. — The main action of the orbicularis oris is to bring the lips together, 

 closing the mouth, and if its action be continued, it will press the lips against the teeth. 



Its more peripheral fibres, aided by 

 Fig. 501, the incisive bundles, will tend to pro- 



Pyramidalis nasi tfudc the lips. 



2. Nasalis (Fig. 501). 



Attachments. — The nasalis 



forms a thin sheet which arises from 

 the maxilla in close association with 

 the incisive bundles of the upper lip. 

 The more medial fibres, the pars alaris 

 (^depressor alee fiasi), are inserted into 

 the alar cartilage of the nose, while 

 the more lateral ones, the pars trans- 

 versa yconpressor nariimi) , often re- 

 ceiving slips from the adjacent levator 

 labii superioris alaeque nasi and the 

 levator anguli oris, extend forward 

 over the ala of the nose to terminate 

 upon its dorsal surface in a thin aponeurosis which unites it to the muscle of the 

 opposite side. 



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

 Action. — The more median fibres draw the alar cartilage downward and in- 

 ward, while the more lateral ones slighdy depress the tip of the nose and at the same 

 time compress the nostril. 



Levator labii 

 sup. alaeque 

 nasi, nasal 

 portion cut 

 away 



Depressor alse nasi 



Orbicularis oris 



Compressor 

 narium 

 / >Dilatores naris 



Depressor septi 



Muscles of the nose. 



