inferior frontal gyrus
The inferior frontal gyrus makes up the lateral and inferior surface of the frontal lobe and is separated from the middle frontal gyrus above by the inferior frontal sulcus. It contains the frontal operculum (hiding the anterosuperior part of the insular cortex).
Its inferior edge abuts the lateral sulcus (Sylvian fissure), which gives off two branches that subdivide the inferior frontal gyrus into three parts. From anterior to posterior: the anterior ramus (a.k.a. anterior horizontal ramus) separates the pars orbitalis from the pars triangularis, and the ascending ramus (aka anterior ascending ramus) separates the pars triangularis form the pars opercularis.
These three parts of the frontal operculum (orbitalis, triangularis, and opercularis) result in the inferior frontal gyrus having a characteristic "M" configuration sometimes referred to as the M sign .