risorius
noun
ri·so·ri·us
| \ ri-ˈsōr-ē-əs
, -ˈzȯr-
\
, -ˈzȯr-
\
plural risorii\ -ē-ˌī
\
\
Medical Definition of risorius
: a narrow band of muscle fibers arising from the fascia over the masseter muscle, inserted into the tissues at the corner of the mouth, and acting to retract the angle of the mouth