THE FIFTH, TRIGEMINAL, OR TRIFACIAL NERVE 983 



along the outer wall of the cavernous sinus (Figs. 505 and 506V below the oculo- 

 motor and trochlear nerves (Fig. 731), and just before entering the orbit, through 

 the sphenoidal fissure, divides into three branches lacrimal, frontal, and nasal . 



Branches of Communication. The ophthalmic nerve is joined by filaments 

 from the cavernous plexus of the sympathetic, and gives off minute branches 

 to communicate with the oculomotor and abducent nerves, and not infrequently 

 with the trochlear. 



Branches of Distribution. It gives off recurrent filaments (;?.. tentorii) which 

 pass between the layers of the tentorium cerebelli, and then divides into 



Lacrimal. Frontal. Nasal. 



The lacrimal nerve (n. lacrimalis) (Figs. 733 and 734) is the smallest of the three 

 branches of the ophthalmic. It sometimes receives a filament from the trochlear 

 nerve, but this is possibly derived from the branch of communication which 

 passes from the ophthalmic to the trochlear. It passes forward in a separate 

 tube of dura, and enters the orbit through the narrowest part of the sphenoidal 

 fissure (Fig. 738). In the orbit it runs along the upper border of the External 

 rectus muscle, with the lacrimal artery, and communicates with the temporomalar 

 branch of the superior maxillary nerve. It enters the lacrimal gland and gives 

 off several filaments, which supply the gland and the conjunctiva. Finally, it 

 pierces the superior palpebral ligament, and terminates in the integument of the 

 upper eyelid, joining with filaments of the facial nerve. The lacrimal nerve is 

 occasionally absent, when its place is taken by the temporal branch of the superior 

 maxillary. Sometimes the latter branch is absent, and a continuation of the 

 lacrimal is substituted for it. 



The frontal nerve (n.Jrontalis) (Figs. 729 and 733) is the largest division of the 

 ophthalmic, and may be regarded, both from its size andMirection, as the continu- 

 ation of the nerve. It enters the orbit above the muscles, through the sphenoidal 

 fissure^ (Fig. 738), and runs forward along the middle line, between the Leva tor 

 palpebrae and the periosteum. Midway between the apex and the base of the 

 orbit it divides into two branches, supratrochlear and supraorbital. 



The supratrochlear branch (n. supratrochlear is] (Fig. 729), the smaller of the 

 two, passes inward, above the pulley of the Superior oblique muscle, and gives 

 off a descending filament, which joins with the infratrochlear branch of the nasal 

 ^ve. It then leaves the orbit between the pulley of the Superior oblique and 

 the supraorbital foramen, curves up on to the forehead close to the bone, ascends 

 beneath the Corrugator supercilii and Occipitofrontalis muscles, and, dividing 

 into branches which pierce these muscles, it supplies the integument of the lower 

 part of the forehead on either side of the middle line and sends filaments to the 

 conjunctiva and skin of the upper eyelid. 



The supraorbital branch (n. supraorbitalis) (Fig. 738) passes forward through 

 the supraorbital foramen, and gives off, in this situation, palpebral filaments to 

 the upper eyelid. It then ascends upon the forehead, and terminates in cutaneous 

 and pericranial branches. The cutaneous branches, two in number, an inner and' 

 an outer, supply the integument of the cranium as far back as the vertex. They 

 arc at first situated beneath the Occipitofrontalis, the inner branch perforating 

 the frontal portion of the muscle, the outer branch its tendinous aponeurosis. 

 The pericranial branches are distributed to the pericranium over the frontal and 

 parietal bones. 



The nasal nerve (n. nasociliaris) (Figs. 729 and 733) is intermediate in size 

 between the frontal and lacrimal, and is more deeply placed than the other branches 

 of the ophthalmic. It enters the orbit by way of the sphenoidal fissure (Fig. 

 738) between the two heads of the External rectus, and passes obliquely inward 

 across the optic nerve., beneath the Superior rectus and Superior oblique muscles, 



