Page 229 - My FlipBook

BLOOD-VESSEL SYSTEM OF THE HEAD, ETC. 239

terminal ones, which pass to tlie npper eyelid and the conjunctiva, and
anastomose ^ith branches of other arteries distributed to this region of
the face. One or two small twigs pass from the artery through for-
amina in the malar bone to the temporal fossa, anastomosing with the
deep temporal artery. Small branches also pass through the same
bone and anastomose with the deep and superficial arteries of the
check, which are branches of the transverse facial. A branch from the
lachrymal, which is given off soon after its origin, passes backward
through a notch in the margin of the anterior lacerated foramen, sup-
plies the dura mater, and anastomoses with the middle meningeal artery.
Other branches are distributed to the membrane covering the outer
wall of the orbit, the external and superior recti muscles, and the
levator palpebrse superioris muscles.
The Central Retinal Artery is a small branch arising from the oph-
thalmic soon after it passes out of the optic foramen. It passes
obliquely through the centre of the optic nerve, about a quarter of an
inch posterior to its point of entrance into the eyeball, and is distributed
to the retina and the hyaloid membrane. During embryonic life this
artery has a central branch which passes forward through the middle of
the vitreous humor of the eye to the posterior portion of the lens, upon
which it is lost.
The Ciliary Arteries are divided into a posterior and anterior set, the
former being subdivided into short and long ciliary arteries.
The Short Ciliary Arteries number four or five, and arise from the
ophthalmic as it crosses the optic nerve. They soon divide into twelve
or fifteen small branches, which pass forward in a tortuous or spiral
course through the adipose tissue surrounding the optic nerve to the
posterior part of the eyeball, Avhere they pierce the sclerotic coat in close
proximity to the entrance of the optic nerve. Passing through the
sclerotic, they enter the choroid coat, and immediately break up into a
minute capillary plexus which forms the greater part of the internal
coat of the choroid. From the anterior portion of this plexus small
vessels are given off which pass to the ciliary processes.
The Lovf/ Ciliary Arteries are two in number, and but slightly larger
than the short ciliary vessels. They pass forward, one on each side
of the. eyeball, and enter the sclerotic coat, passing between it and
the choroid to the ciliary ligaments, where they each divide into two
The four branches then diverge and
branches, superior and inferior.
pass forward to the periphery of the iris (circulus major), where they
reunite and form an arterial circle. From this circle branches are dis-
tributed to the iris, some of the concentric extremities uniting to form
an inner circle (circulus minor) on the free or pupillary margin of
the iris.
The Anterior Ciliary Arteries number six or eight, and arise from
the muscular and lachrymal branches. They communicate freely with
each other, and form a vascular circle around the anterior portion of the
eyeball between the conjunctiva and the sclerotic coat of the eye. From
tiiis circle small vessels pass through the sclerotic coat one or two lines
posterior to the margin of the cornea, and join the external vascular
circle of the iris.