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ri·so·ri·us (mus·cle)

facial muscle of mouth; origin, from platysma and fascia of masseter; insertion, orbicularis oris and skin at corner of mouth; action, draws angle of mouth laterally, lenghthening rima oris; nerve supply, facial.


Etymology: L, ridere, to laugh
one of the 12 muscles of the mouth. A muscular fibrous band, it arises in the fascia over the masseter and inserts into the skin at the corner of the mouth. It acts to retract the angle of the mouth, as in a smile.


(rī-sŏ′rē-ŭs) [L., laughing]
The muscular fibrous band arising over the masseter muscle and inserted into the tissues at the corner of the mouth.

risorius (risō´rēəs),

n a muscle of facial expression in the orofacial re-gion that is used when smiling widely.
References in periodicals archive ?
Inasmuch as the risorius muscles often (but not in sad human expression) are frequently cooperative with the zygomatics, old adages such as "sing with a pleasant expression," "breathe as though inhaling the fragrance of a rose," etc.
It was used macroscopic dissection and direct observation of the orbicular muscles of the lips, depressor of angle of mouth, risorius and elevator of upper lip and wing of nose.
Fleeting facial expressions are expressed by minute and unconscious movements of facial muscles like the frontalis, corregator, and risorius," Frank explains.
the marginal mandibular branch to the risorius muscle and the muscles of the lower lip and chin
the mandibular lamina (the depressor labii inferioris, the mentalis, the risorius, the depressor anguli oris, the inferior part of the orbicularis oris, and perhaps the buccinator and the levator anguli otis)
The toxin is typically injected into the zygomaticus major and minor, the levator anguli oris, and the risorius.