The =periorbita= or ocular sheath is a conical fibrous membrane which
incloses the eyeball with its muscles, vessels, nerves, etc. Its apex is
attached around the optic and lacerated foramina, and its base is in
part attached to the bony rim of the orbit, in part continuous with the
fibrous layer of the lids. Its inner part, which is in contact with the
orbital wall, is thin; incorporated with it beneath the root of the
supraorbital process is the bar of cartilage around which the superior
oblique muscle is reflected. The outer part is thicker, and is
strengthened by an elastic band which is attached to the pterygoid crest
and furnishes origin to the thin unstriped orbital muscle. A quantity of
fat (Corpus adiposum extraorbitale) lies about the periorbita, and
within it is the intraorbital adipose tissue (Corpus adiposum
intraorbitale) which fills the interstices between the eyeball, muscles,
etc.