56 DISSECTION OF THE ORBIT. 



superior angle. A second branch of considerable thickness (short root *) 

 passes from the inferior angle to join the branch of the third nerve that 

 supplies the inferior oblique muscle. And the third root is derived from the 

 sympathetic (the cavernous plexus), either in union with the long root, or 

 as a distinct branch to the posterior border of the ganglion. 



Branches. The short ciliary nerves (fig. 11) are ten or twelve in 

 number, and are collected into two bundles, which leave the upper and 

 lower angles of the front of the ganglion. In the upper bundle are four or 

 five, and in the lower, six or seven nerves. As they extend along the 

 optic nerve to the eyeball they occupy the outer and under parts, and com- 

 municate with the long ciliary branches of the nasal nerve. 



The OPHTHALMIC ARTERY, a branch of the internal carotid, is trans- 

 mitted into the orbit through the optic foramen. At first the vessel is 

 outside the optic nerve, but it then courses inwards, over or under the 

 nerve, to the inner angle of the orbit, where it ends in a nasal branch 

 (external) on the side of the nose (fig. 17, n ), and anastomoses with the 

 angular and nasal branches of the facial. 



The branches of the artery are numerous, though inconsiderable in size, 

 and may be arranged in three sets : one arising outside the optic nerve, 

 another above it, and a third set on the inner side. 



The lachrymal artery accompanies the nerve of the same name to the 

 upper eyelid, where it ends by supplying that part, and anastomosing with 

 the palpebral arches. It supplies branches, like the nerve, to the lachry- 

 mal gland and the conjunctiva ; and it anastomoses with the middle men- 

 ingeal by an offset through the sphenoidal fissures. 



At the front of the orbit it sends a small branch with each of the ter- 

 minal pieces of the temporo-malar nerve ; and these join the temporal and 

 transverse facial arteries. 



The central artery of the retina is a very small branch which pierces 

 the optic nerve, and so reaches its destination in the eyeball. 



The supra-orbital branch arises beneath the levator palpebrse and supe- 

 rior rectus muscles ; it then takes the course of the nerve of the same 

 name through the notch in the margin of the orbit, and ends in branches 

 on the forehead (p. 21). As it winds round the margin of the orbit it sup- 

 plies the eyelid and the orbicularis muscle. 



The ciliary branches are uncertain in their place of origin and enter 

 the eyeball at the front and back : 



The posterior ciliary, about twelve in number, are continued to the 

 eyeball around the optic nerve, and perforate the sclerotic coat at the pos- 

 terior part. Two of this set (one on each side of the optic nerve), named 

 long ciliary, pierce the sclerotic farther out than the others, and lie along 

 the middle of the eyeball. 



The anterior ciliary arteries arise from muscular branches of the oph- 

 thalmic, and perforate the sclerotic coat near the cornea : in the eyeball 

 they anastomose with the posterior ciliary. For the ending of these vessels, 

 see the eyeball. 



The muscular branches are not fixed in their place of origin ; and those 

 to the lower muscles often arise together as one trunk. 



The ethmoidal branches are two, anterior and posterior, and are directed 

 through the foramina in the inner wall of the orbit: 



The posterior is the smaller of the two, and furnishing small meningeal 

 offsets (anterior) to the dura mater of the base of the skull, descends into 



