MASSETER—THE TEMPORAL MUSCLE 441 



muscle; covering also the deep surface of the gland, and giving off a process called 

 the stylo-maxillari/ ligament, which, running from the styloid process to the angle 

 of the mandible, separates the parotid and submaxillary glands. 



1. MASSETER 



The masseter (fig. 311) — named from the Greek word /j.a(jd()tj.m, to chew — is a 

 strong quadrate sheet, consisting of two layers. 



Origin. — The superficial layer, from the lower border of the malar bone, and the 

 lower border of the anterior two-thirds of the zygomatic arch; the deep layer, from 

 the lower border of the posterior third of the zygomatic arch, and the whole of its 

 inner surface. 



Insertion. — The superficial layer, into the lower lialf of the outer surface of the 

 ranuis of the mandible; the deep layer, partly with the superficial layer, and jwirtly 

 into the upi)er half of the outer surface of the ramus of the mandible. 



Structure. — The origin and insertion are by tendinous bands intermingled in 

 multipenniform fashion with fleshy fibres. The fibres of the superficial sheet are 

 directed obliquely downwards and backwards; those of the deep sheet almost 

 vertically downwards, and they are much shorter than the superficial fibres. The 

 two sheets blend closely in front, but are separate behind, where the muscle forms 

 a sort of pocket closed above at the origin and below at the insertion, as Avell as in 

 front, but ojien behind. 



Nerve-supply. — The masseteric branch of the motor portion of the mandilmlar 

 division of the fifth nerve, which enters the deep surface of the muscle just l^elow 

 the zygoma. 



Action. — To close the jaw, and by its superficial layer to draw it slightly 

 forwards. In closing the jaw it acts with less mechanical disadvantage than is 

 usual witb muscles. When the pressure to be overcome is exerted upon the ))ack 

 teeth, the arm of the lever upon Avhich the power acts is almost as long as that 

 which intervenes between these teeth and the fulcrum. This fulcrum is not at the 

 temporo-mandilmlar joint, but at a j^oint below the neck of the mandible, cor- 

 responding very nearly to the lower attachment of the internal lateral ligament. 

 Moreover, the resultant force of the muscle, acting as it does upwards and forwards, 

 is perpendicular to the lever, which may be roughly described as a bar extending 

 downwards and forwards from the neck of the mandible to the point of the chin. 



Relations. — Superficially, the parotid gland and its duct, the platysma 

 myoides, the risorius and the masseteric fascia, the transverse facial vessels, the 

 facial vein, the upper and lower divisions of the facial nerve; deeply, the buccal 

 fat-pad which separates it from the buccinator and a small part of the temporal 

 muscle. 



2. THE TEMPORAL MUSCLE 



The temporal muscle — named from its attachment to the temple ( = (empus) 

 — is a thick, somewhat triangular sheet; more correctly it may be described as 

 forming the quadrant of a circle. 



Origin. — (1) The whole of the temporal fossa, from the temporal to the ptery- 

 g<Md ridge, with the exception of a small part close to the outer wall of the orljit. 

 which is occu])ied by fat; (2) the inner surface of the temporal fascia down to its 

 lower attachment to the zygomatic process, from the inner surface of which some 

 of its fibres also sometimes arise. 



Insertion. — The point, posterior border, and the whole of the inner surface of 

 the coronoid process of the mandible, down to the last molar tooth. 



Structure. — The bones of the temjioral fossa and tlie temporal fascia form a 

 pouch, open downwards, from which the fleshy fibres of the muscle converge, 

 the middle fibres running downwards, the anterior downwards and backwards, the 

 l)osterior almost transversely forwards, to be inserted beloAV upon both faces of a 

 flat tendon which, becoming free of flesh on the outer surface first, embraces the 

 point and borders of the coronoid process. 



