•ZYGOMATICUS MAJOR— RISORIUS 437 



1. ZYGOMATICUS MAJOR 



The zygomaticus major — iianictl from its origin from the zygoma and its size 

 — is rihl)on-shaped, and belongs to the first layer of the museles. 



Origin. — The outer surface of the malar bone near the zygomatic suture. 



Insertion. — The deep surface of the skin, and the sul)cutaneous tissue at the 

 outer extremity of the upper lip, and just external to the commissure of the lips. 



Structure. — Arising liy short tendinous fibres, the muscle forms a fleshy band 

 which passes downwards and forwards to the meeting-point of the angular muscles 

 at and external to the angle of the mouth, where it blends with the orbicularis oris 

 and the other angular muscles, its outermost fibres passing into the outer fibres of 

 the depressor anguli oris. 



Nerve-supply. — The infraorbital branch of the upper division of the facial 

 ner\-e, wliich enters the middle of its deep surface. 



Action. — To draw upwards and outwards the corners of the mouth, as in 

 smiling or laughter. When it is strongly contracted, it throws into prominence 

 the soft parts of the cheek in front of the malar l^one, raises the lower eyelid, and 

 produces 'crow's feet,' as the wrinkles are called which radiate outwards from 

 the outer canthus. "When both muscles act together, the mouth is Avidened, and 

 the upper lip raised so as to shoAV the upper teeth, in what is called a ' broad 

 grin.' 



Relations. — Superficially, the skin; deeply, the buccinator and facial part of 

 the orbicularis oris, the facial and transverse facial arteries, the facial vein, and 

 some branches of the facial nerve. 



2. LEVATOR ANGULI ORIS 



The levator anguli oris — named from its action upon the corner of the mouth 

 — is a triangular sheet and belongs to the second stratum of the facial muscles. 



Origin. — The canine fossa of the maxilla. 



Insertion. — The deep surface of the skin, and the subcutaneous tissue, close to 

 the corner of the mouth. 



Structure. — Arising muscular from its broad origin al)ove the canine and 

 bicuspid teeth, the fibres converge in a downward and outward direction, and blend 

 with the other angular muscles outside the corner of the mouth. 



Nerve-supply. — The infraorbital branch of the upper division of the facial at 

 the outer i)art of the anterior surface. 



Action. — To raise the corner of the mouth, Ijut at the same time to draw it 

 inwards. 



Relations. — Superficially, the zygomaticus minor and levator laliii superioris, 

 the infraorljital vessels and nerves; deeply, the facial portion of the orbicularis oris. 



3. RISORIUS 



The risorius — named from its supposed action in laughter — is flat and ribbon- 

 shaped, and belongs to the superficial layer of muscles, being a part of the platysma 

 myoides, and often very small and ill-developed. 



Origin. — The subcutaneous tissue overlying the deep fascia which covers the 

 masscter and parotid gland. 



Insertion. — The sul)cutaneous and muscular tissue external to the angle of the 

 mouth. 



Structure. — It. is a band of ])arallcl filnvs which runs transversely forwards 

 from tlx' upper and posterior part of the ])latysma to the corner of the mouth. 



Nerve-supply. — The buccal 1>ranch of tlie lower division of the facial nerve 

 which enters it from lieneath. 



Action. — To widen the mouth by drawing its corner directly outwards. It is 

 not used in the expression of pleasure like the zygomaticus major. Init it gives a 



