OPHTHALMIC GANGLION, one of the four cephalic ganglia of the great sym pathetic nerve. It is about the size of a pin's head, and situated at the back part of the orbit, between the optic nerve and the external rectus muscle. It lies iu a quantity of loose fat which makes its dissection somewhat difficult.. It has three branches of communi cation which enter its posterior border. The long branch is derived from the nasal branch of the ophthalmic nerve (first division of the 5th nerve). The second branch, or root, is derived from a branch of the third nerve supplying the inferior oblique muscle of the eyeball. The third branch, or root, is a slender filament from the cavernous plexus of the sympathetic. According to Tiedemann this ganglion receives a filament of communication from Meekel's ganglion (q.v.). Its branches of distribution are the short ciliary nerves. These are 10 or 12 delicate filaments arifing from the fore-part of the ganglion iu two bundles. They run forward with the ciliary arteries, pierce the
sclerotic coat at the back part of the globe, pass forward in delicate grooves on its inner surface, and arc distributed to the ciliary muscle and the iris. It is therefore seen that the ophthalmic ganglion is one of the most important nerve centers in the whole body, although no larger than a pin's head. The ciliary muscle is the muscle of accommo dation of the eye, causing variation in the form of the aqueous humor and the crys talline lens so as to accommodate focal length of the eye to the distance of objects. Its supply of nerve force to the muscular fibers of the iris is also intimately connected with the focal length of the eye-apparatus, and its connections with this part of the eye are of marvelously beautiful character.