The inferior opthalmic vein begins in a venous net-work at the forepart of the floor and medial wall of the orbit; it receives some vorticose veins

Vorticose veins

The vorticose veins, referred to clinically as the vortex veins, drain the ocular choroid. The number of vortex veins is known to vary from 4 to 8 with about 65% of the normal population having 4 or 5. In most cases, there is at least one vortex vein in each quadrant...

 and other veins from the Rectus inferior, Obliquus inferior, lacrimal sac

Lacrimal sac

The lacrimal sac is the upper dilated end of the nasolacrimal duct, and is lodged in a deep groove formed by the lacrimal bone and frontal process of the maxilla...

 and eyelids, runs backward in the lower part of the orbit and divides into two branches.

One of these passes through the inferior orbital fissure

Inferior orbital fissure

Not to be confused with the infraorbital groove, infraorbital canal, and infraorbital foramen.The lateral wall and the floor of the orbit are separated posteriorly by the inferior orbital fissure which transmits the maxillary nerve and its zygomatic branch, and the ascending branches from the...

 and joins the pterygoid venous plexus, while the other enters the cranium through the superior orbital fissure and ends in the cavernous sinus

Cavernous sinus

The cavernous sinus , within the human head, is a large collection of thin-walled veins creating a cavity bordered by the temporal bone of the skull and the sphenoid bone, lateral to the sella turcica.-Contents:...

, either by a separate opening, or more frequently in common with the superior opthalmic vein.