1234 HUMAN ANATOMY. 



Within the orbit the lachrymal nerve communicates with the temporal branch 

 of the temporo-malar nerve and on the face with the temporal branch of the facial. 

 The latter is one of the numerous sensory-motor communications between the 

 terminal fibres of the fifth and seventh nerves. 



Variations. — Occasionally the lachrymal nerve seems to be partly derived from the troch- 

 lear ; the true source of such fibres, however, is probably the ophthalmic nerve, by way of its 

 communicating branch to the fourth. Considerable variation is found in connection with the 

 temporal branch of the temporo-malar nerve. The lachrymal nerve or the temporal branch of 

 the temporo-malar may be absent, the place of either being taken by the other, or the lachrymal 

 may be small at its origin and later increased to normal size by accessions from the temporal 

 branch of the temporo-malar. 



4. The frontal nerve (n. frontalis) (Fig. 1053) is the largest branch of the 

 ophthalmic. It enters the orbit, invested by its own dural sheath, through the 

 sphenoidal fissure and above the orbital muscles and passes directly forward between 

 the periosteum and the levator palpebrae superioris. At a variable point, usually 

 about the middle of the orbit, it divides into its terminal branches, the (a) supra- 

 trochlear and {b) the supraorbital. 



a. The supratrochlear nerve (n. supratrochlearis) is the smaller of the two terminal 

 branches. It passes inward and forward over the pulley of the superior oblique and thence 

 between the orbicularis palpebrarum and the frontal bone, leaving the orbit at its upper inner 

 angle. Near the pulley it gives off a branch which joins the infratrochlear (Fig. 1057) and at 

 the edge of the orbit supplies filaments (nn. palpebrales superiores) to the skin and conjunctiva of 

 the upper eyelid. It then turns upward and subdivides into a number of small branches which 

 pierce the substance of the frontalis and orbicularis palpebrarum muscles to supply the inner 

 and lower part of the forehead. 



b. The supraorbital nerve (n. supraorbitalis) (Fig. 1056) continues directly the course of 

 the frontal nerve. It lies close to the periosteum throughout its entire orbital course and leaves 

 the orbit through the supraorbital notch or foramen. In this situation it sends a small filament 

 to the frontal sinus to supply its diploe and mucous membrane. As it leaves the orbit it sup- 

 plies some fine twigs to the upper eyelid and then divides into a larger outer and smaller inner 

 branch. These pass upward on the forehead beneath the frontalis muscle, occasionally occupy- 

 ing quite deep grooves in the frontal bone, and terminate by being distributed to the scalp and 

 pericranium. The outer branch extends back nearly to the occipital bone, while the inner 

 passes only a short distance posterior to the coronal suture. 



Both branches of the frontal, the supratrochlear and the supraorbital, communicate with 

 branches of the facial nerve and thereby supply sensory filaments to muscles supplied by the 

 seventh. 



Variations. — The nerve may divide before leaving the orbit and in that event only the outer 

 branch passes through the normal osseous channel. The inner sometimes has a special groove, 

 named by Henle \hQ frontal notch. 



5. The nasal nerve (n. nasociliaris) (Fig. 1057) is intermediate in size 

 between the lachrymal and the frontal. It enters the orbit, clothed in dura mater, 

 through the sphenoidal fissure, between the heads of the external rectus and between 

 the superior and inferior divisions of the oculomotor nerve. Turning obliquely in- 

 ward, it crosses the optic nerve and passes beneath the superior oblique and superior 

 rectus muscles and above the internal rectus. Thence it traverses the anterior eth- 

 moidal foramen to enter the cranial cavity, where it passes forward in a groove in 

 the lateral part of the cribriform plate of the ethmoid bone. Leaving the cranium 

 through the nasal fissure, the nerve enters the nasal fossa, where it breaks up into 

 *ts three terminal branches. 



« Branches. — These are: {a) the gajigliojiic, (b) the lofig ciliary, (c) the i?t/ra- 

 trochlear, {d) the internal nasal, ((?) the exter7ial nasal and (/) the anterior nasal, of 

 which the last three are terminal branches. 



a. The ganglionic branch (radix longa) (Fig. 1057) usually leaves the nerve between the 

 heads of the external rectus and passes forward along the outer side of the optic nerve to enter 

 the upper posterior portion of the ciliary ganglion, of which it forms the sensory or long root. 



b. The long ciliary branches (nn. ciliares longi) (Fig. 1058) are two in number. They pass 

 forward along the inner side of the optic nerve and, after joining one or more of the short ciliary 

 nerves, pierce the sclerotic coat of the eye to be distributed to the iris, ciliary muscle and cornea. 



