Vascular Anatomy of the Anteriorly Based Frontal Pericranial Flap. A, Frontal region with the skin and galea-frontalis layer reflected forward leaving the pericranium attached to the bone. The supraorbital artery anastomoses medially with branches of the supratrochlear artery and laterally with branches of the superficial temporal artery. The supratrochlear artery anastomoses medially with branches of the dorsal nasal artery. The veins in the supraorbital area form a large transverse channel called the transverse supraorbital vein, into which the superficial branches from the galea-frontalis layer and deep branches from the pericranium empty. There are also some tiny anastomoses distally between the superficial and deep branches of the arteries that are divided when the galea-frontalis layer is separated from the pericranium. B, Medial view of a sagittal section of the right frontal region. The skin and galea-frontalis layer have been reflected forward, leaving the pericranium attached to the bone. In the most common pattern, the supraorbital and supratrochlear arteries divide into superficial and deep branches at the level of orbital rim as shown. C, In 20% of cases, the main trunk of the supraorbital artery divides into superficial and deep pericranial branches several millimeters above the level of the orbital rim. The deep branch would be transected if the separation of the galeal-frontalis layer from the pericranium extended down to the orbital rim. D, When a supraorbital foramen is present as shown, the deep branch of the supraorbital nerve and a small deep pericranial artery usually pass through the foramen. The larger superficial trunk of the supraorbital artery and part of the nerve usually pass around the supraorbital rim rather than through the supraorbital foramen as shown. (Images courtesy of AL Rhoton, Jr.)