l8o ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 262. — The deeper layer of the facial muscles. 

 The quadratus labii superioris, zygomaticus, triangularis, quadratus labii inferioris, the parotideo-masseteric fascia, 

 the parotid gland, and a portion of the superficial layer of the temporal fascia have been removed. 



Fig. 263. — The oral musculature seen from behind. 

 The muscles, together with the integument, have been separated from the bones, and the mucous membrane covering 

 the muscles has been removed. 



mal ridge of the lachrymal bone and the fibers pass horizontally across the lachrymal sac to the 

 margins of the lids, where they decussate and disappear in the fibers of the palpebral portion. (A 

 more detailed description will be found in the section upon "The Eye.") 



The orbicularis oculi, like all of the facial muscles, is supplied by the seventh cranial or facial nerve. 



Its function is to close the palpebral fissure. The fibers of the lachrymal portion facilitate the entrance of the 

 lachrymal secretion into the lachrymal canaliculi and also assist it onward, and those fibers which pass to the eyebrow and 

 the forehead, wrinkle the skin in these regions. 



THE ORAL MUSCLES. 



The muscles of the oral region consist of the buccinator, of the circular fibers situated about 

 the mouth which form the orbicularis oris, of the muscles of the upper lip, of the muscles of the 

 lower lip, of muscles which are situated upon the skin, and of muscles which radiate into the 

 angles of the mouth. The great majority of these muscles are intimately connected with each 

 other. 



The quadratus labii superioris (Figs. 260 and 262) is situated in the upper lip in the 

 nasal, infraorbital, malar, buccal, and superior labial regions. 



It has in general a triangular shape and arises by three heads: the angular head from the 

 bony bridge of the nose in connection with the frontalis and the orbicularis oculi ; the infraorbital 

 head, arising broadly from the infraorbital margin and covered by the orbital portion of the 

 orbicularis oculi; and the zygomatic head, a slender fasciculus from the malar surface of the 

 zygomatic bone, which is usually adherent to the lateral radiations of the orbicularis oculi. 



The angular head (levator labii superioris alaique nasi) is composed of two portions, an inner 

 one passing to the ala of the nose (levator alee nasi), and a stronger outer one which unites with 

 the two other heads of the quadratus and passes to the musculature of the upper lip near the inner 

 side of the angle of the mouth. The infraorbital head (levator labii superioris) is the broadest, 

 and the somewhat inconstant zygomatic head (zygomaticus minor) the longest head of the muscle. 

 At the insertion of the quadratus labii superioris into the upper lip its muscular fibers interlace 

 with those of the orbicularis oris. 



The zygomaticus (zygomaticus major) (Fig. 260) is an elongated, rather strong, and easily 

 isolated muscle which is situated in the malar, buccal, and oral regions. It has an independent 

 origin from the malar surface of the malar bone, close beside the zygomatic head of the quadratus 

 labii superioris, and runs to the angle of the mouth, where it fuses with the orbicularis oris and 

 the neighboring muscles. 



The risorius or "smiling" muscle (Figs. 260 and 267) is a thin, approximately triangular 

 muscle of variable development which is situated chiefly in the parotideo-masseteric and buccal 

 regions. It arises from the parotideo-masseteric fascia (see page 184), sometimes extending 



