Pars orbitalis

The pars orbitalis refers refers to the orbital partmost rostral portion of the inferior frontal gyrus on the inferolateral surface of in the frontal lobe of the brain. It is one of three parts that make up the most rostralinferior frontal gyrus along with the pars triangularis and pars opercularis^4-6. It plays a role in the language processing network of the three parts of the inferior frontal gyrus and is separated from the brain.

Gross anatomy

Relations

The pars triangularis byorbitalis lies ventral to the anterior horizontal ramus (a.k.a. anterior ramus) of the lateral sulcus (a.k.a. Sylvian fissure). It extends along the ventral most part of the lateral surface of the frontal lobe as far as the caudal segment of the lateral orbital sulcus ^4-6.

Blood supply

It is supplied by the frontal branches of the middle cerebral artery.

Radiographic features

Radiographically the pars orbitalis can be identified as the most rostral portion of the inferior frontal gyrus which takes on a characteristic “M” configuration. This area approximately correspondsis also referred to as the M sign when identifying the inferior frontal gyrus ³.

Function

Although the pars orbitalis is not defined by cytoarchitecture, it is closely affiliated to Brodmann area’s areas 47/12 ^1-3. Traditionally not considered to be a core language area, new studies suggest in the dominant hemisphere it plays a more significant role in language processing with its involvement in semantic processing, phonological processing and syntax ¹. The function of the same cortical region in the non-dominant hemisphere is not as well documented but has been shown to be involved in behavioural and motor inhibition and deductive reasoning ².