334 THE MUSCULATURE 



Variations. — The risorius is very inconstant in its development, and in its relations to 

 neighbouring muscles, and is not infrequently quite small. The zygomaticus is rarely absent 

 Its origin may extend to the temporal or masseteric fasciae. It may be doubled throughout its 

 length or at one extremity. Frequently the triangularis is divided into three fasciculi. 



The buccinator (fig. 343) arises from — (1) the molar portion of the alveolar process of the 

 maxilla; (2) the buccinator crest of the mandible, and (3) the pterygo-mandibular raphe of the 

 bucco-pharyngeal fascia. This narrow fibrous band, which separates the buccinator from the 

 superior constrictor of the pharynx, extends from the pterygoid hamulus to the buccinator crest 

 of the mandible. The fibre-bundles are divisible into four sets. The most cranial extend 

 directly into the orbicularis of the upper lip. The next pass through the commissure at the 

 corner of the hps into the orbicularis of the lower lip; the third through the commissure into the 

 orbicularis of the upper lip, and the fourth directly into the orbicularis of the lower lip. The 

 muscle is attached chiefly to the mucosa of the lips near the angle of the mouth. Some fibre- 

 bundles extend to the more medial portion of the mucosa and some through the orbicularis to 

 the skin. 



Nerve-supply. — By the buccal branch of the facial nerve through filaments which enter the 

 posterior half of its outer surface. 



Relations. — The muscle is covered externally by the thin bucco-pharyngeal fascia; internally 

 by the mucosa of the mouth. Above its outer surface lie the zygomatic (z. major), risorius, and 

 masseter muscles. Between the last and the buccinator lies a large pad of fat (the buccal fat 

 pad). The parotid duct passes forward over the muscle, and slightly in front of its centre 

 pierces it and passes into the mouth. It is crossed by the external maxillary (facial) artery and 

 anterior facial vein and by the buccal artery and nerve. 



Actions. — It draws the corner of the mouth laterally, puUs the lips against the teeth, and 

 flattens the cheek. It is of use in mastication, swallowing, whistling, and blowing wind- 

 instruments. 



Variations. — Occasionally it consists of two laminae, a condition found in many mammals. 

 It may be continuous in part with the superior constrictor of the pharynx, as in the cat. 



(c) MENTAL MUSCLE 



The mentalis (levator menti) (fig. 343) is a short, thick muscle which arises from the alveolar 

 jugum of the lower lateral incisor tooth and the neighbouring region of the mandible under 

 cover of the quadratus (depressor) labii inferioris and beneath the oral mucosa, where this is 

 reflected from the lips to the gums. It extends to the chin, where it is fused with the muscle 

 of the opposite side and is attached to the skin of the chin. 



Nerve-supply. — The mandibular branch of the seventh nerve sends terminal twigs into this 

 muscle. 



Actions. — It draws up the skin of the chin and thus indirectly causes the lower lip to pro- 

 trude. It is of use in articulation, in forcing bits of food from between the gums, and in the 

 expression of various emotions (muscle of pride). 



Variations. — It varies greatly in size and generally is fused with the platysma. 



(d) NASAL MUSCLES 

 (Figs. 341 and 344) 



Toward the nasal apertures several muscles converge. Those extending from 

 above elevate and dilate, those from below depress and contract, the nostrils. 

 To the former belongs the pars transversa of the nasalis (compressor naris), a 

 triangular muscle extending from the bridge of the nose to the naso-labial sulcus; 

 the caput angulare of the quadratus labii superioris (levator labii superioris 

 alffique nasi), which arises from the root of the nose and sends a fasciculus to the 

 wing of the nose; and the dilatores naris, described below; to the latter, the 

 pars alaris of the nasalis (depressor alic nasi), which extends from the alveolar 

 juga of the upper lateral incisor and canine teeth to the dorsal margin of the 

 nostril; and the small depressor septi nasi. 



The nasalis consists of two parts, the pars transversa and the pars alaris. The pars trans- 

 versa (compressor naris) is triangular. It lies on the side of the nose above the wing. Its 

 filtre-bvuidles arise from an aponrnirosis which oviM-fies the bridge of the nose, is adherent to the 

 skin, and is not closely attached to the underlying cartilage. From this aponeurosis the fibre- 

 bundles converge toward the back of the wing, where they are attached to the skin along the 

 line whicli separates the wing from the cheek (naso-labial sulcus). Its insertion is covered bj' 

 the na.sal prr)cess of the caput angulare (levator labii superioris altcque nasi) of the quadratus 

 labii superioris (p. 332), with which its fil)rcs interdigitatc. An attachment (origin) is also 

 described by many as taking ))lace in the lower part of Ihe canine fossa of the maxilla. 



'J'lie pars alaris (doi)roHHor ahc nasi) (fig. 343), is a small quadrangular nuisclo situated below 

 the aperture of the nose, between this and the alveolar portion of the maxilla. It is covered by 

 the nmcosa of the gum, by the orbicularis oris and the quadratus (levator) labii superioris, and 

 laterally is fu.sed with the pars transversa (compres.sor naris). It arises from the alveolar juga 

 of the lateral inci.sor and (he canine teeth. Its fibre-bundles extend vertically to the skin of 

 the dorsal margin of tlic nostril, from the dorsal part of the cartilage of the wing to the septum 



The depressor septi is a flat, triangular muscle whi(!h extends from the orbicularis oris to 

 the lower edge of the na.sal septum. It nuiy arise from the jugum alveolarc of the medial 

 incisor. 



