Insula and Limen Recess. A, Anteroinferior view of the anterior perforated substance and the limen recess in left hemisphere. The frontoparietal and temporal opercula have been retracted to expose the anteroinferior part of the insula. The limen recess is the area between the medial edge of the limen insulae and the point at which the most lateral LSA enters the anterior perforated substance. It has a mean width of 15 mm. No LSAs enter this area. The anterior perforated substance is usually considered to extend lateral to the limen insulae; however, the limen recess is devoid of perforating branches and forms the lateral limit of the anterior perforated substance. The accessory gyrus, located in front of the anterior short gyrus, blends below into the transverse gyrus. The transverse gyrus, the shortest of all insular gyri, connects the anterior edge of the insula to the posterior orbital gyrus. B, Enlarged inferolateral view of another left cerebral hemisphere. The frontoparietal operculum has been removed, and the temporal operculum has been retracted to expose the insula. The limen insulae extends from the anterior end of the long gyri, where it fuses with the temporal pole, to the posterior orbital gyrus. The limen recess lies between the point of entry of the most lateral LSA into the anterior perforated substance and limen insulae. The transverse gyrus is positioned between the insular pole and the posterior orbital gyri. C, Inferior view of left cerebral hemisphere. The anterior perforated substance forms the roof of the sphenoidal compartment of the sylvian fissure. The right temporal lobe has been removed down to the level of the temporal stem. The anterior perforated substance has a salt-and-pepper appearance, created by small openings through which the perforating arteries and veins penetrate the hemisphere. The limen recess, located between the point at which the most lateral LSA enters the anterior perforated substance and the limen insulae, is devoid of openings for perforating arteries. (Images courtesy of AL Rhoton, Jr.)