274 MUSCLES OF THE HEAD AND NECK. 



oris, by the terminal fibres of the platysma myoides, and by the masseter and 

 zygomatici. from which it is separated by a quantity of eoft adipose tissue of 

 a peculiar character. Oj^posite the second molar tooth of the upper jaw, its 

 fibres give passage to the duct of the parotid g-land. 



The depressor anguli oris, or triangularis oris muscle, is liroad 

 at its origin from the external oblique line of the lower jaw ; passing 

 upwards it is collected into a narrower bundle, which is inserted into 

 the orbicularis at the angle of the mouth. 



Iichition>t. — This muscle is covered by the skin, and at its insertion, by the 

 zygomaticus major, under which its fibres pass ; it conceals part of the buc- 

 cinator and of the depressor of the lower lip. 



Varictij. — The transversalls vwnti (Santorini) is a small band of muscular 

 fibres sometimes found arising from the inner border of the depressor, and 

 cui"ving do^\Tiwards and inwards below the chin towards the mesial line of the 

 neck. 



The depressor laljii inferioris, or quadratus luenti muscle, arises 

 from the lower jaw by a line of attaclnnent extending from near the sym- 

 physis to a little beyond the mental foramen ; thence it ascends with 

 an inward inclination, unites with its fellow, and blending with the 

 orbicularis oris is inserted into the lower lip. Its fibres are intermixed 

 with much adipose matter. 



The levator labii inferioris, or levator inenti muscle, arises by a 

 narrow head from the incisor pit of the lower jaw, and, expanding in 

 a nearly vertical plane, is directed downwards, and slightly forwards 

 and inwards, between the depressors of the lower lip, to the integu- 

 ment of the chin. 



Nei'ves. — All the superficial muscles of the face previously described receive 

 their motor nerves from one soiu'ce. viz.. the facial motor, or portio dura of the 

 seventh pair, twigs from this widely distributed nerve being sent even into 

 the occipitalis muscle. Tlie expression of the passions by the varying state of 

 the skin of the forehead and eyebrows, the eyelids, nostrils and mouth, the 

 closure of the eyelids, the dilatation of the nostrils in breathing, and the move- 

 ments of the lips m the prehension of food and othei"wise, together with the 

 movements of the scalp and external ear, when they are possible, — are all under 

 the influence of the facial nerve, which has thus been reckoned as a nerve of 

 respiration and expression. 



Actions. — llie orbicularis oris acting alone draws the lips together in both 

 the vertical and transverse dii'ections. Acting in conjunction with the bucci- 

 nators it closes the lips, while at the same time they are elongated transversely. 

 Its facial j:iortion acting alone projects the lips. The labial portion, when acting 

 in concert with the converging muscles, tightens the lips, one or both, against 

 the teeth. The convergent muscles each draw their oral points of insertion in a 

 direction coiTesponding to that of their muscular fibres. Tlie common elevator 

 of the lij") and nose and the uj^per i^art of the orbicularis oris act on both the 

 upper lip and the ala of the nose together — the one elevating the other depressing 

 them. ■\\Tien the cheeks are distended with air, and the aperture of the lips 

 naiTOwed, it is by the action of the buccinator that the forced expulsion of the 

 air is effected and regulated. The le-\-ator menti not only draws upwards the 

 integument of the chin, but it also protrudes the lower lip, as in ijoiiting. The 

 muscles attached to the angles of the mouth are, along with others of the face, 

 intunately connected with the expression of the passions : those which pass 

 dowTiwards not only raise the upper lip, but also irash upwards the cheek, and 

 thus elevate the margin of the lower eyelid, as in mirth : and tliose which 

 descend from the angle of the mouth depress that part, as in grief. (On the 

 action of the facial muscles may be consulted, more especially. Sir Charles Bell, 

 " Anatomy and Philosophy of Expression," and Duchene, "' Mechanisme de la 

 Physionomie Humaine," Paris, 18G2, and " Physiol, des Mouvements," &;c., 1867.) 



