inferior frontal gyrus


Short definition

This part of the database is still under construction.

Definition - HNS

HNS2: Paxinos, G. and Mai, J.K.: The Human Nervous System, 2nd Ed. Academic Press/Elsevier, San Diego, 2004.
HNS3: Mai, J.K. and Paxinos, G.: The Human Nervous System, 3rd Ed. Academic Press/Elsevier, San Diego, 2011.

Inferior frontal gyrus

Lateral Surface of the Frontal Lobe; Precentral region


Petrides, Pandya (HNS2):


            The inferior frontal gyrus constitutes a large part of the ventrolateral surface of the prefrontal cortex. It is delimited dorsally by the horizontally directed inferior frontal sulcus (ifs) and ventrally by the rostral part of the lateral fissure (Figs. 1 and 2).  In a caudorostral direction, the inferior frontal gyrus can be divided into three parts: the pars opercularis, the pars triangularis and the pars orbitalis.  The pars opercularis is delimited caudally by the inferior precentral sulcus and rostrally by the ascending sulcus (as), i.e. the ascending ramus of the lateral fissure.  The pars triangularis lies between the ascending sulcus and the horizontal sulcus (hs), also known as the horizontal ramus of the lateral fissure.  The pars orbitalis lies ventral to the horizontal sulcus as far as the lateral orbital sulcus.  The pars opercularis is seen usually as a vertically oriented gyrus that is subdivided into a rostral and a caudal part by the diagonal sulcus (ds).  In different brains, a variable extent of the caudal part of the pars opercularis is submerged into the inferior precentral sulcus (see Tomaiuolo et al., 1999).  Depending on the curvature of the pars opercularis and how much of it stays on the surface of the brain, the diagonal sulcus may appear to lie in the middle of the pars opercularis clearly separating it into two parts, or it may appear to join any of the surrounding sulci.


            Within the pars triangularis, there is usually a small sulcus, the triangular sulcus (ts), also known as the incisura capitis.  There may be an additional more rostrally located sulcus that is directed towards the pars triangularis and which Eberstaller (1890) named the sulcus radiatus (r).  The inferior frontal sulcus originates, caudally, close to the inferior precentral sulcus and, in many cases, there is a clear separation between these two sulci.  In other cases, the narrow bridge of cortex that separates them may be submerged and the inferior frontal sulcus and the inferior precentral sulcus merge superficially.  Eberstaller (1890) pointed out that the inferior frontal sulcus extends rostrally until about the mid-portion of the dorsal edge of the pars triangularis of the inferior frontal gyrus.  Our recent investigation of the frontal sulci in 80 cerebral hemispheres has confirmed Eberstaller’s observations.  In some textbooks (e.g. Ono et al., 1990), the term “inferior frontal sulcus” has been used loosely to include other sulci, such as the sulcus radiatus and the lateral frontomarginal sulcus, that lie anterior to it and, sometimes, abut superficially with it. The tendency to treat these distinct sulci as rostral extensions of the inferior frontal sulcus introduces considerable confusion in the identification of the frontal sulci.  For instance, we observed that, although in some cases the sulcus radiatus and the lateral frontomarginal sulci may anastomose and appear to join superficially the rostral end of the inferior frontal sulcus, these three sulci could be clearly separated by careful examination of sections of the frontal lobe.



Definition - other sources



Classical Architecture





Functional Anatomy

Clinical Anatomy



Figures, Diagrams, Tables